Axis axis is a moderately large deer standing 88-97cm at the shoulders. It has a rufous brown coat that is covered with white spots on the abdomen, rump, throat, insides of legs and ears and underside of tail that persist throughout the life of the animal. A dark stripe runs down the back from the nape to the tip of the tail. A gland-bearing cleft is present on the front of the pastern of the hind foot. A. axis dental formula is similar to elk, Cervus elaphus, but the upper canines (the so-called "elk teeth") are lacking. Males measure an average total length of 1.7m with a tail 200mm in length and their height at the shoulder can reach 90cm. Females are generally smaller. Weights can reach 66-113kg in males and 43-66kg in females (Mungall and Sheffield, 1994). Antlers are present only on bucks, and immediately upon shedding a set of antlers, growth begins on the next set. The larger the antlers, the longer the development period, from "velvet" through to "hard" antler. Antlers over 76cm take roughly five months to fully develop. Each antler has three tines;the brow tine forms at near right angle with the beam and the front (or outer) tine of the terminal fork is much longer than the hind (or inner) tine.
Shrubs up to 3 m tall, finely pubescent throughout, branches and stems quadrangular. Leaves membranous, broadly ovate to triangular-ovate, 6-25 cm long, 5-25 cm wide, both surfaces sparsely to moderately strigillose, margins coarsely and irregularly dentate, apex acute, and base cordate to truncate. Inflorescences terminal, cymose, densely many-flowered, subsessile or short-pendulate, often subtended by a pair of foliaceous bracts, bracteoles numerous, oblong or elliptic, 1.5-3 cm long, strigillose, especially along the margins. Flowers are fragrant, calyx purple or red, sometimes with white spots, campanulate, 10-15 mm long, 5-lobed, the lobes anceolate, apex acuminate, corolla pale pink, usually doubled by petaloid stamens, stamens and ovary usually modified into extra petals. Fruits are rarely developed (Liogier, 1995, Wagner et al., 1999).
An erect or spreading annual, up to 1.5 m tall but generally shorter. Stems cylindrical or slightly ridged, densely clothed with long, fine, spreading, grey or reddish-brown pubescence. Stipules linear, setaceous, up to 1 cm long. Five to seven leaflets, occasionally nine, elliptical-oblong, up to 40 mm long and 25 mm wide, the terminal one rather longer than the lateral, pilose on both surfaces. Inflorescence a dense, many-flowered raceme, hirsute, 20 to 30 cm long, including a peduncle more than 25 mm long. Bracts linear-lanceolate, up to 25 mm long. Pedicels around 1 mm long, reflexed in fruit. Calyx stiff, brown and hirsute, about 4 mm long, divided almost to the base into linear, setaceous lobes. Corolla white pubescent outside, brick-red or rose inside. Pods straight, rather tetragonal, with well-developed sutures, 12 to 20 mm long about 2 mm wide, thickly hirsute, many of the hairs, especially the dorsal ones, usually brown. Six to nine seeds, cuboid, angular, strongly pitted (FAO, 2013). In China, flowers July-September and fruits between October and December (e Floras, 2013).
L. gulosus has a deep, laterally compressed body. Adults are olive-coloured with mottled sides and wavy lines on the cheek and gold-coloured on the ventral side (Etnier, 1993). The gill flaps are often red and there are 3-5 reddish-brown streaks radiating from the eyes (Texas Parks and Wildlife, 2015). L. gulosus has 3 anal spines and 10 dorsal spines (Texas Parks and Wildlife, 2015). This fish ranges in length from 10 to 30 cm. The mouth is terminal and large. The upper jaw extends to the middle of the eye or farther, with their lower jaw protruding noticeably beyond the upper jaw (Mettee et al., 1996). L. gulosus has a well-developed pad of lingual teeth and patches of teeth on the palatine bones (Ross, 2001).
Eggs, grey in colour, are laid as a single mass. After hatching, male moths typically develop through five larval instars before pupation, while females have a sixth larval stage. The larva has been described (Riotte, 1979). Tufts on abdominal segments 1-4 are grey or brown. Adult males are day flying (23 mm wingspan), while females are apterous (16 mm length) (Hoare, 2001).
A. macrorrhizos is a glabrous, terrestrial herb, normally around 1-1.5 m tall but growing up to 5 m (Manner, 2011). Plants are acaulescent with a short, conical corm, produce watery sap and develop an elongated caudex with age. Leaves are arranged in a rosette, ascending;blades flattened, ascending, with basal sinus projecting downward, 25-50 (-100) ? 20-36 (-100) cm, green (although white-variegated in some cultivars), slightly lustrous, lance-ovate, coriaceous, wavy or slightly plicate along secondary veins, the apex acute or obtuse and apiculate, the base hastate, the sinuses non-overlapping, up to 30 cm long, the margins wavy, with a submarginal vein within 2 mm from the margin;mid-vein broad and conspicuous with 4-7 primary lateral veins per side;lower surface with dark spots on secondary vein angles;petioles 60-100 cm long. Two or more inflorescences subtended by brachts. Peduncles 20-45 cm long;spathe a whitish to yellowish green, oblong tube;spadix 11-32 cm, pistil 3-4 cm long and about 1.5 cm thick. Fruit a fleshy berry, red when mature, globose or ovoid (Flach and Rumawas, 1996;Wagner et al., 1999;Acevedo-Rodr’guez and Strong, 2005).
X. citri is a Gram-negative, straight, rod-shaped bacterium measuring 1.5-2.0 x 0.5-0.75 µm. It is motile by means of a single, polar flagellum. It shares many physiological and biochemical properties with other members of the genus Xanthomonas. It is chemoorganotrophic and obligately aerobic with the oxidative metabolism of glucose. Colonies are formed on nutrient agar plates containing glucose and are creamy-yellow with copious slime. The yellow pigment is xanthomonadin. Catalase is positive, but Kovacs' oxidase is negative or weak;nitrate reduction is negative. Asparagine is not used as a sole source of carbon and nitrogen simultaneously;various carbohydrates and organic acids are used as a sole source of carbon. Hydrolysis of starch, casein, Tween 80 and aesculin is positive. Gelatine and pectate gel are liquefied. Growth requires methionine or cysteine and is inhibited by 0.02% triphenyltetrazolium chloride. Biovars may be distinguished by utilization of mannitol. For further information on the bacteriological properties of X. citri, see Goto (1992).
Strains of groups B, C and D have many properties in common with group A, the differences being detected by the utilization of only a few carbohydrates (Goto et al., 1980).
Features of citrus-attacking xanthomonads including X. citri and the genus Xanthomonas as a whole, have been characterized at the molecular level for the development of quick and accurate methods for reclassification and identification. The procedures include DNA-DNA hybridization (Vauterin et al., 1995), genomic fingerprinting (Lazo et al., 1987), fatty acid profiling (Yang et al., 1993), SDS-PAGE (Vauterin et al., 1991) and isoenzyme profiles (Kubicek et al., 1989) and monoclonal antibodies (Alverez et al., 1991).
Phage-typing is applicable to X. citri with greater reliability than any other plant pathogenic bacterium investigated so far. Many strains of X. citri are lysogenic (Okabe, 1961). Two virulent phages, Cp1 and Cp2, can infect 98% of the strains isolated in Japan (Wakimoto 1967). Similar results were also obtained in Taiwan (Wu et al., 1993). The filamentous temperate phages and their molecular traits have been studied in detail (Kuo et al., 1994;Wu et al., 1996). Phage Cp3 is specific to the canker B strains (Goto et al., 1980). No phages specific to canker C and D strains have been isolated.
Methods of detecting X. citri from natural habitats include leaf-infiltration, bacteriophage, fluorescent antibody and ELISA (Goto, 1992). The polymerase chain reaction and dot blot immunobinding assay (DIA) were developed for rapid, sensitive, and specific detection of the pathogen. The detectable limits were reported to be around 30 c.f.u./ml for the former and 1000 c.f.u./ml for the latter (Hartung et al., 1993, 1996;Wang et al., 1997;Miyoshi et al., 1998).
Canker lesions begin as light yellow, raised, spongy eruptions on the surface of leaves, twigs and fruits. The lesions continuously enlarge from pin-point size over several months and can be of many different sizes based on the age of the lesion. As the lesions enlarge, the spongy eruptions begin to collapse, and brown depressions appear in their central portion, forming a crater-like appearance. The edges of the lesions remain raised above the surface of host tissue and the area around the raised portion of the lesion may have a greasy appearance. The lesions become surrounded by characteristic yellow halos. Canker lesions retain the erupted and spongy appearance under dry conditions, such as in a greenhouse;whereas they quickly enlarge and turn to flat lesions with a water-soaked appearance with frequent rain. Canker lesions vary in maximum size from 5 to 10 mm, depending on the susceptibility of the host plant. The symptoms are similar on leaves, fruit and stems.
Canker lesions are histologically characterized by the development of a large number of hypertrophic cells and a small number of hyperplastic cells. At an early stage of infection, the cells increase in size and the nuclei and nucleoids stain more easily;there is also an increase in the amount of cytoplasm synchronized with rapid enlargement. However, these hypertrophied cells do not divide;cell division is only detected in the peripheral areas of lesions adjacent to healthy tissue.
The lesions of canker B, C and D are similar in appearance and histology to those of canker A (Goto, 1992).
Reddy and Naidu (1986) reported canker lesions on roots;however, this has not been confirmed.
X. citri is a bacterial pathogen that causes citrus canker - a disease which results in heavy economic losses to the citrus industry worldwide either in terms of damage to trees (particularly reduced fruit production), reduced access to export markets, or the costs of its prevention and control. Lesions appear on leaves, twigs and fruit which cause defoliation, premature fruit abscission and blemished fruit, and can eventually kill the tree. It is introduced to new areas through the movement of infected citrus fruits and seedlings, and inadvertent re-introduction is highly likely despite the quarantine restrictions that are in place in many countries. Locally, X. citri is rapidly disseminated by rainwater running over the surfaces of lesions and splashing onto uninfected shoots;spread is therefore greatest under conditions of hight temperature, heavy rainfall and strong winds. Some areas of the world have eradicated citrus canker, others have on-going eradication programmes, however, this pathogen remains a threat to all citrus-growing regions.
The Citrus species listed in the table of hosts, and the following hybrids, are natural hosts of X. citri, with varying degrees of susceptibility to X. citri. In addition to host plant, susceptibility is also affected by the plant part affected, whether leaves, fruits or twigs. Reddy and Naidu (1986) reported canker lesions on roots but this has not been confirmed.
C. aurantiifolia x Microcitrus australasica (Faustrime), C. limon x M. australasica (Faustrimon), C. madurensis x M. australasica (Faustrimedin), C. sinensis x Poncirus trifoliata (Citrange), C. paradisi x P. trifoliata (Citrumelo) (Schoulties et al., 1987), C. aurantifolium x P. trifoliata (Citradia), C. nobilis x P. trifoliata (Citrandin), C. unshiu x P. trifoliata (Citrunshu), Citrange x P. trifoliata (Cicitrangle), C. adurensis x Citrange (Citrangedin), C. deliciosa x Citrange (Citrangarin), C. unshiu x Citrange (Citranguma), Fortunella margarita x Citrange (Citrangequat), F. japonica x C. aurantiifolia (Limequat), C. maxima x C. aurantiifolia (Limelo), C. madurensis x C. aurantiifolia (Bigaraldin), C. maxima x C. sinensis (Orangelo), F. margarita x C. sinensis (Orangequat), C. nobilis (Clementine) x C. maxima (Clemelo), C. nobilis (King of Siam) x C. maxima (Siamelo), C. unshiu x C. maxima (Satsumelo), C. deliciosa x C. maxima (Tangelo), C. nobilis (King of Siam) x C. sinensis (Siamor), C. deliciosa x C. madurensis (Calarin), C. unshiu x C. madurensis (Calashu). C. aurantiifolia x F. marginata is immune (Reddy, 1997).
Other than Citrus species and their hybrids, most plants, except P. trifoliata, are not sufficiently susceptible to X. citri under natural conditions to warrant attention as hosts of the bacterium. Although the potential of these plants as natural hosts seems to be negligible, further investigation is necessary because no confirmative host surveys have been undertaken since the 1920s. Species names within the genus Citrus also merit some attention due to their inconsistent use by authors.
Plants other than Citrus spp.:
Unless otherwise stated, the following plants refer to Peltier and Frederich (1920, 1924) who defined susceptibility on the basis of artificial inoculation in the greenhouse (G) and/or in the field (F): Aeglopsis chevalieri (G), Atalantia ceylonica (G), Atalantia citrioides (G), Atalantia disticha (G) (Lee, 1918), Chalcas exotica (G), Casimiroa edulis (G, F), Chaetospermum glutinosum (G, F), Clausena lansium (G), Citropsis schweinfurthii (G), Eremocitrus glauca (G, F), Evodia latifolia (G), Evodia ridleyei (G), Feronia limonia [ Limonia acidissima ] (G), Feroniella lucida (G, F), Feroniella crassifolia (G), Fortunella hindsii (G, F), Fortunella japonica (G, F), Fortunella margarita (G, F), Hesperethusa crenulata (G, F), Lansium domesticum (G), Melicope triphylla (G), Microcitrus australasica (G, F), Microcitrus australasica var. sanguinea (G, F), Microcitrus australis (G, F), Microcitrus garrowayi (G, F), Paramignya monophylla (G), Paramignya longipedunculata (G) (Lee, 1918), Poncirus trifoliata (G, F), Xanthoxylum clava-herculis [ Zanthoxylum clava-herculis ] (G, F), Xanthoxylum fagara [ Zanthoxylum fagara ] (G, F) (Jehle, 1917). Atalantia ceylanica, A. monophylla, Microcitrus australis, Feronia limonia and Severinia buxifolia are immune (Reddy, 1997). In India, goat weed (Ageratum conyzoides) is reported to be a host (Pabitra et al., 1997) but confirmation is needed.
The following plants have also been reported as susceptible to X. citri, however, the original descriptions were either not confirmed (U) or contradict those of other authors (C): Aegle malmelos (C), Balsamocitrus paniculata (U), Feroniella obligata (U), Matthiola incana var. annua (U) and Toddalia asiatica (C).
Of the primary hosts listed, yuzu is highly resistant (Goto, 1992) and calamondins, Cleopatra mandarin and Sunki mandarin are immune (Reddy, 1997). Both Fortunella japonica and F. margarita are highly resistant (Goto, 1992).
Cuscuta species have a very distinct appearance, consisting mainly of leafless, glabrous, yellow or orange twining stems and tendrils, bearing inconspicuous scales in the place of leaves. In C. campestris, the yellow to pale orange true stems, about 0.3 mm in diameter, generally do not twine and attach to the host, but produce tendrils of similar appearance, arising opposite the scale leaves, which do form coils and haustoria (Dawson, 1984). The seedling has only a rudimentary root for anchorage, while the shoot circumnutates, i.e. swings round anti-clockwise about once per hour, until it makes contact with any stem or leaf, round which it will coil before growing on to make further contacts. The root and shoot below this initial attachment soon die, leaving no direct contact with the soil. Haustoria form on the inside of the coils and penetrate to the vascular bundles of susceptible hosts. Flowers, each about 2 mm across, occur in compact clusters 1-2 cm across. There is a calyx of 5 fused sepals with obtuse or somewhat acute lobes, and 5 corolla lobes, triangular, acute, often turned up at the end, equalling the length of the tube. Stamens alternate with the corolla lobes, each with a fringed scale below. The ovary is almost spherical with a pair of styles with globose tips. The capsule reaches 2-3 mm across when mature, with a depression between the two styles. The capsule does not dehisce and seeds remain on the plant long after maturity. Seeds are irregular in shape, rough-surfaced, about 1 mm across.
The presence of Cuscuta is always obvious from the twining stems and tendrils. Symptoms of damage are not especially characteristic, but reflect the very powerful sink effect created by the haustoria, resulting in reduced vigour and, in particular, poor seed and fruit development.
The parasitic weed C. campestris is native to North America but has been introduced around the world and become a weed in many countries. It is by far the most important of the dodders, perhaps because of its wide host range. This ensures that there is a wide range of crop seeds that may be contaminated, and in which it may be introduced to new areas over both short and long distances. Once introduced it is almost certain that there will be suitable host plants on which it can thrive and be damaging, whether they are crops or wild species. Vegetative spread can be very rapid – up to 5 m in 2 months. It also has a wide tolerance of climatic conditions from warm temperate to sub-tropical and tropical.
The host range of C. campestris is extremely wide. Several hundred crop and weed species have been listed as hosts, though some of these may only be acting as secondary hosts after the parasite is established on a more favoured primary host (e.g. Gaertner, 1950;Kuijt, 1969). Most are dicotyledonous, though the monocot onion can be seriously attacked. The plant is most important as a pest of lucerne and other legumes. Grasses sometimes appear to be acting as hosts but are not normally penetrated. The literature on host range is usefully reviewed by Cooke and Black (1987). Crops commonly parasitized, other than those listed in the table, include asparagus, chickpea, lentil, grape, citrus, melon, Lespedeza and flower crops including chrysanthemum. Not all hosts are consistently attacked, for example tomato is susceptible when young but becomes resistant with age (Gaertner, 1950).
Measurements (after Nickle et al., 1981)
Female lectotypes (n=5): L=0.52 (0.45-0.61) mm;a=42.6 (37-48);b=9.6 (8.3-10.5);c=27.2 (23-31);V=74.7 (73-78)%;stylet=12.8 (12.6-13.0) µm.
Male lectotypes (n=5): L=0.56 (0.52-0.60) mm;a=40.8 (35-45);b=9.4 (8.4-10.5);c=24.4 (21-29);stylet=13.3 (12.6-13.8) µm;spicule=21.2 (18.8-23.0) µm.
Measurements (after Mamiya and Kiyohara, 1972)
Female (n=40): L=0.81 (0.71-1.01) mm;a=40.0 (33-46);b=10.3 (9.4-12.8);c=26.0 (23-32);V=72.7 (67-78)%;stylet=15.9 (14-18) µm.
Male (n = 30): L=0.73 (0.59-0.82) mm;a=42.3 (36-47);b=9.4 (7.6-11.3);c=26.4 (21-31);stylet=14.9 (14-17) µm;spicules=27.0 (25-30) µm.
Description (after Nickle et al., 1981)
Female: cephalic region high, offset, with six lips. Stylet with small basal swellings. Oesophageal gland lobe slender and about 3-4 body-widths long. Excretory pore located at about the level of the oesophago-intestinal junction, occasionally at the same level as the nerve ring. Hemizonid about 0.67 of a body-width behind the median bulb. Vulva posterior, the anterior lip overhanging to form a flap. Genital tract monoprodelphic, outstretched. Developing oocytes mostly in single file. Post-uterine sac well developed, extending for 0.75 or more of the distance to the anus. Tail subcylindroid with a broadly rounded terminus. Mucron usually absent, but some populations may have a short, 1-2 µm, mucron.
Male: similar to female in general respects. Spicules large, strongly arcuate so that the prominent transverse bar is almost parallel to the body axis when the spicules are retracted. The apex is bluntly rounded and the rostrum prominent and pointed. The distal tip of each spicule is expanded into a disc-like structure named the cucullus. The tail is arcuate with a pointed, talon-like terminus bearing a small bursa. Seven caudal papillae are present;one pair adanal, a single preanal ventromedian papilla, and two postanal pairs near the tail spike and just anterior to the start of the bursa.
B. xylophilus on its natural hosts behaves like other members of the genus, living a mycophagous life cycle on trees weakened or damaged by other causes. When introduced into new continents, it encounters new host species of Pinus, some of which are exceptionally susceptible, so that the nematode follows a 'phytophagous' life cyle. Readily transmitted by local Monochamus spp., it invades and destroys pine forests.
A. citrulli is Gram-negative, obligately aerobic, and motile with a single polar flagellum (Willems et al., 1992). Cells are straight to slightly curved rods that are 0.2 to 0.8 by 1.0 to 5.0 um. On nutrient agar, colonies are round with slightly scalloped or spreading margins. Colonies are convex, smooth to slightly granular, and beige to faintly yellow with a translucent marginal zone. Colonies are non-fluorescent on King's medium B.
Initial symptoms of A. citrulli in watermelon seedlings appear as water-soaked areas on the underside of cotyledons and leaves (Webb and Goth, 1965). In young seedlings, lesions can develop in the hypocotyl resulting in collapse and death of the emerging plant. As cotyledons expand, water-soaked lesions turn dark brown and often extend along the length of the midrib. Leaf lesions are light brown to reddish-brown and frequently spread along the midrib of the leaf (Latin and Hopkins, 1995). As the growing season progresses, leaf symptoms may become sparse and inconspicuous.
The characteristic symptom of bacterial fruit blotch in watermelon is a dark, olive-green blotch on the upper surface of infected fruit that begins as a small, water-soaked area a few millimetres in diameter and rapidly enlarges to a lesion several centimetres in diameter with irregular margins (Somodi et al., 1991). In a few days, the lesions may expand to cover the entire upper surface of the fruit, leaving only the groundspot symptomless. Initially, the lesions do not extend into the flesh of the watermelon. In advanced stages of lesion development, the initial infection site may become necrotic. Cracks in the rind surface may occur, resulting in fruit rot. Rotting watermelon fruit often ooze a sticky, clear, amber substance or an effervescent exudate (Latin and Hopkins, 1995).
Seedling and leaf symptoms on other cucurbits are similar to those on watermelon. Symptoms on muskmelon fruit consist of water-soaked pits on the fruit surface (Latin and Hopkins, 1995). In honeydew fruit, lesions begin as water soaked spots that, with age, become brown and cracked in the centre with a water-soaked margin. The lesions in honeydew are usually 3-10 mm in diameter.
Symptoms can be produced in all cucurbits tested by inoculation, especially in the seedling stage (Schaad et al., 1978;Latin and Hopkins, 1995). Watermelon, cantaloupe and honeydew melons appear the most susceptible, with both foliar symptoms and blotch symptoms on the fruit (Isakeit et al., 1997). Symptoms develop on inoculated foliage of squash, cucumbers and other cucurbits, but fruit symptoms have not been observed on these hosts. Citron (Citrullus lanatus var. citroides), a common weed in parts of the southern USA, is also a host for A. citrulli. Symptoms are produced on the foliage and fruit, and seed transmission occurs in this cucurbit weed, giving it the potential to serve as an alternate host to perpetuate the bacterium.
In host range studies, symptoms were produced on tomato, eggplant and pepper foliage, but not on fruit.
R. solanacearum is a Gram-negative bacterium with rod-shaped cells, 0.5-1.5 µm in length, with a single, polar flagellum. The positive staining reaction for poly-ß-hydroxybutyrate granules with Sudan Black B or Nile Blue distinguishes R. solanacearum from many other (phytopathogenic) Gram-negative bacterial species. Gram-negative rods with a polar tuft of flagella, non-fluorescent but diffusible brown pigment often produced. Polyhydroxybutyrate (PHB) is accumulated as cellular reserve and can be detected by Sudan Black staining on nutrient-rich media or the Nile Blue test, also in smears from infected tissues (Anonymous, 1998;2006) On the general nutrient media, virulent isolates of R. solanacearum develop pearly cream-white, flat, irregular and fluidal colonies often with characteristic whorls in the centre. Avirulent forms of R. solanacearum form small, round, non-fluidal, butyrous colonies which are entirely cream-white. On Kelman’s tetrazolium and SMSA media, the whorls are blood red in colour. Avirulent forms of R. solanacearum form small, round, non-fluidal, butyrous colonies which are entirely deep red.
The bacterium may be obtained from infected tubers or stems for staining purposes if a small portion of tissue is pressed onto a clean glass slide. Potato tubers can be visually checked for internal symptoms by cutting. Suspect tubers should be diagnosed in the laboratory. Appropriate laboratory methods to detect the pathogen have been laid down in a harmonized EU-interim scheme for detection of the brown rot bacterium (Anon., 1997). These methods are based on earlier described indirect immunofluorescence antibody staining (IFAS). Standard samples of 200 tubers per 25 t of potatoes are taken (Janse, 1988;OEPP/ EPPO, 1990a;Anon., 1997, 1998, 2006). Recently a very effective selective medium has been described (Engelbrecht, 1994, and modified by Elphinstone et al., 1996), that can also be applied for detection in environmental samples such as surface water, soil and waste (Janse et al., 1998;Wenneker et al., 1999). ELISA and PCR, based on 16S rRNA targeted primers as well as fluorescent in-situ hybridization (FISH) using 16S and 23S rRNA-targeted probes have also been used.
Ralstonia syzygii, causal agent of Sumatra disease of clove (Syzygium) and the distinct Blood Disease Bacterium, causal agent of blood disease of banana in Indonesia, are closely related to R. solanacearum and cross-react in serological and DNA-based detection methods (Wullings et al., 1998;Thwaites et al., 1999).
Foliage: the first visible symptom is a wilting of the leaves at the ends of the branches during the heat of the day with recovery at night. As the disease develops, a streaky brown discoloration of the stem may be observed on stems 2.5 cm or more above the soil line, and the leaves develop a bronze tint. Epinasty of the petioles may occur. Subsequently, plants fail to recover and die. A white, slimy mass of bacteria exudes from vascular bundles when broken or cut.
Tubers: external symptoms may or may not be visible, depending on the state of development of the disease. Bacterial ooze often emerges from the eyes and stem-end attachment of infected tubers. When this bacterial exudate dries, soil masses adhere to the tubers giving affected tubers a 'smutty' appearance. Cutting the diseased tuber will reveal browning and necrosis of the vascular ring and in adjacent tissues. A creamy fluid exudate usually appears spontaneously on the vascular ring of the cut surface.
Atypical symptoms on potato (necrotic spots on the epidermis), possibly caused after lenticel infection, have been described by Rodrigues-Neto et al. (1984).
Symptoms of brown rot may be readily distinguished with those of ring rot caused by Clavibacter michiganensis subsp. sepedonicus (EPPO/ CABI, 1997). R. solanacearum can be distinguished by the bacterial ooze that often emerges from cut stems and from the eyes and stem-end attachment of infected tubers. If cut tissue is placed in water, threads of ooze are exuded. Because such threads are not formed by other pathogens of potato, this test is of presumptive diagnostic value. For ring rot, tubers must be squeezed to press out yellowish dissolved vascular tissue and bacterial slime.
The youngest leaves are the first to be affected and have a flaccid appearance, usually at the warmest time of day. Wilting of the whole plant may follow rapidly if environmental conditions are favourable for the pathogen. Under less favourable conditions, the disease develops slowly, stunting may occur and large numbers of adventitious roots are produced on the stem. The vascular tissues of the stem show a brown discoloration and drops of white or yellowish bacterial ooze may be released if the stem is cut (McCarter, 1991).
One of the distinctive symptoms is partial wilting and premature yellowing of leaves. Leaves on one side of the plant or even a half leaf may show wilting symptoms. This occurs because vascular infection may be restricted to limited sectors of stems and leaf petioles. In severe cases, leaves wilt rapidly without changing colour and stay attached to the stem. As in tomato, the vascular tissues show a brown discoloration when cut. The primary and secondary roots may become brown to black (Echandi, 1991).
On young and fast-growing plants, the youngest leaves turn pale green or yellow and collapse. Within a week all leaves may collapse. Young suckers may be blackened, stunted or twisted. The pseudostems show brown vascular discoloration (Hayward, 1983). Moko disease, caused by R. solanacearum, is easily confused with the disease caused by Fusarium oxysporum f.sp. cubense. A clear distinction is possible when fruits are affected - a brown and dry rot is only seen in Moko disease.
Seedling wilt manifests itself as yellowing of the mature lower leaves, which show scorching and browning of the tissue between the veins. The younger leaves and terminal shoot become flaccid and droop. Affected seedlings show either a gradual loss of leaf turgidity or sudden wilting. Seedling wilt becomes evident in the early hours of the day and gradually becomes more pronounced by midday, especially on sunny days. The wilted seedlings may partially recover during the afternoon and evening when temperatures fall, but wilting becomes more pronounced on successive days. The roots of affected seedlings exhibit a brownish-black discoloration. In advanced stages of disease, the tuberous portion of the root becomes discoloured and spongy. In due course, seedlings with pronounced wilt symptoms become completely desiccated.
In container nurseries, R. solanacearum infects the cotyledons of emerging seedlings causing greyish-brown, water-soaked lesions, which spread to the entire cotyledon and become necrotic. The infection spreads to the adjoining stem and root tissues and the affected seedlings rot and die. Collar rot appears in 1- to 4-month-old bare-root seedlings as greyish-brown, water-soaked lesions at the collar region of seedlings, just above the soil level. The lesions spread longitudinally on the stem, both above and below ground level, becoming sunken and necrotic. The younger leaves become flaccid and droop followed by leaf scorching and pronounced vascular wilt. In bare-root nurseries, wilt usually occurs in small patches affecting individuals or groups of seedlings, which expand as more seedlings succumb to the infection.
Infection of mature foliage begins as greyish-brown to greyish-black, irregular lesions that spread to the entire leaf lamina. Infection spreads to the petioles and stems.
The strains in the race 3 group are a select agent under the US Agricultural Bioterrorism Protection Act of 2002 (USDA, 2005). Peculiarly, the organism, if not yet already present in North America in pelargonium (Strider et al., 1981), was introduced with cuttings of this host by American companies producing these cuttings for their markets in countries like Kenya and Guatamala (Norman et al., 1999, 2009;Kim et al., 2002;Williamson et al., 2002;Williamson et al., 2002;O’ Hern, 2004). A similar situation led to introductions of the pathogen from Kenya into some northern European nurseries. Once the source (contaminated surface water) was recognized and proper control measures (use of deep soil water, disinfection of cutting producing premises and replacement of mother stock), the problem was solved and the disease in greenhouses eradicated (Janse et al., 2004);Similarly race 1 has been introduced into greenhouses with ornamental plants (rhizomes, cuttings or fully grown plants) such as Epipremnum, Anthurium, Curcuma spp. and Begonia eliator from tropical areas (Norman and Yuen, 1998, 1999;Janse et al., 2006;Janse, 2012). Introduction can and did occur from Costa Rica and the Caribbean, Indonesia, Thailand and South Africa. However, this idea of placing pathogens on bioterrorist list for unclear and perhaps industry-driven reasons and its effects, is strongly opposed in a recent publication from leading phytobacteriologists. This is because R. solanacearum is an endemic pathogen, causing endemic disease in most parts of its geographic occurrence, moreover normal quarantine regulations are already in place where the disease is not present or only sporadically and are thought to be more efficient and less damaging to trade and research than placing this pathogen on select agent lists and treating it as such (Young et al., 2008). Peculiarly, it has been used in the control of a real invasive species, the weed kahili ginger (Hedychium gardenarium) in tropical forests in Hawaii. This is not without risks because strains occurring on this weed host were thought to be non-virulent, but later appeared to be virulent on many edible and ornamental ginger species as well (Anderson and Gardner, 1999;Paret et al., 2008). The earlier mentioned tropical strains belonging to phylotype II/4 NPB could become an emerging problem not only in the Caribbean, but also to Southern Europe and North Africa where higher yearly temperatures prevail. Another threat for these countries could be strains belonging to race 1, biovar 1 (phylotype I) that have already been reported from field-grown potatoes in Portugal (Cruz et al., 2008).
R. solanacearum as a species has an extremely wide host range, but different pathogenic varieties (races) within the species may show more restricted host ranges. Over 200 species, especially tropical and subtropical crops, are susceptible to one or other of the races of R. solanacearum. Worldwide, the most important are: tomato, tobacco, aubergine, potato, banana, plantain and Heliconia. Within the EPPO region, race 3 (see Biology and Ecology) with a limited host range including potato, tomato and the weed Solanum dulcamara, is considered to have potential for spread.
Other host crops are: Anthurium spp., groundnut, Capsicum annuum, cotton, rubber, sweet potato, cassava, castor bean and ginger.
Many weeds are alternative hosts of the pathogen. Solanum cinereum in Australia (Graham and Lloyd, 1978), Solanum nigrum and, in rare cases, Galinsoga parviflora, G. ciliata, Polygonum capitata, Portulaca oleracea (for example, in Nepal;Pradhanang and Elphinstone, 1996a) and Urtica dioica have been reported as weed hosts for race 3 (Wenneker et al., 1998). S. nigrum and S. dulcamara are primary wild hosts for race 3.
Lists of host records have been recorded (Kelman, 1953;Bradbury, 1986;Persley, 1986;Hayward, 1994a) but the original reports, gathered over many years, vary greatly in reliability. Few reference strains from reported host plants have been deposited in publicly accessible culture collections to support the authenticity of records.
R. lauricola has been described in detail by Harrington et al. (2008). Optimal colony growth of R. lauricola occurs at 25°C, and cream-buff and smooth colonies develop on malt extract agar that are approximately 60 mm diameter after 10 days (Harrington et al., 2008). Colonies tend to become mucilaginous in their centres and these areas are dominated by budding yeast-like conidia. Colonies that develop from spores tend to be mucilaginous initially and after several days submerged hyphae develop at the colony margins. Conidiophores are hyaline, typically aseptate, and unbranched with lengths variable, usually ranging from 13-60 µm (range 13-120 µm) and 2 µm wide (range 1-2.5 µm). The conidia are hyaline and small, typically 3.5-4.5 µm (range 3.0-8.0 µm) x 1.5-2.0 µm (range 1.0-3.5 µm) and varying from elliptical to ovoid to globose (Harrington et al., 2008).
The detection of laurel wilt in redbay and sassafras is usually straightforward with wilted and dead foliage occurring in some branches initially and eventually over the entire crowns of trees (Fraedrich et al., 2008). A black discolouration is observed in the sapwood of stems and branches. Initially, the discolouration is primarily evident in the outermost sapwood but as the disease progresses the discolouration will be observed through much of the cross-sectional area of the sapwood. Isolation of the pathogen from infected tissues on agar media is necessary to confirm the disease diagnosis. Frass tubes are typically observed on stems and branches of redbay and other species being attacked by X. glabratus, and frequently these are numerous after trees have wilted.
R. lauricola moves rapidly in the xylem of trees (Fraedrich et al., 2015a) and disease symptoms are often observed in portions of redbay trees within two to four weeks after infection. The disease then spreads throughout the entire crown, and redbay trees typically wilt completely within 4 to 12 weeks following inoculation (Fraedrich et al., 2008;Mayfield et al., 2008b). Leaves of infected trees initially droop from loss of turgor and then turn a reddish-brown colour as they die. Some older leaves may initially become chlorotic as they are dying. Leaves on redbay and some other evergreen hosts do not abscise after dying and can be retained on branches for a year or more after the tree has died. A dark black discolouration is observed in the stem and branch sapwood of infected plants. The discolouration is initially observed in the outermost sapwood as localized streaks in the early stages of wilt, but over time the discolouration occurs more extensively throughout the cross-sectional area of the xylem tissue. Symptom development is similar in sassafras and other deciduous hosts except leaves are likely to drop as they die or soon after (Fraedrich et al., 2008;Fraedrich et al., 2015a). Sassafras leaves take on a reddish discolouration (Fraedrich et al., 2008) and pondberry leaves become very chlorotic and turn a bright yellow as they die (Best and Fraedrich, 2018).
The rate of development of the disease and subsequent symptoms in redbay plants depends greatly on their size and environmental factors, such as temperature and moisture conditions. The disease appears to progress relatively slow in trees infected late in the growing season, and trees with partial crown wilt on only a few branches can be found during the winter months. The disease progresses much more rapidly, and trees die quickly, during the spring and summer months when trees are actively transpiring and growing.
Symptom development in avocado is somewhat similar to that of redbay. The first symptom is the wilting of terminal leaves and the development of brown-to-black discolouration as they die (Ploetz et al., 2017a). Unlike redbay, leaves of avocado tend to abscise within 2 to 9 months following symptom development (Ploetz et al., 2017a). Apparently symptoms can be localized in avocado trees with the disease affecting some branches in portions of trees, and epicormic sprouting beneath the affected portions of trees can subsequently lead to the production of healthy branches (Ploetz et al., 2017a). The sapwood of infected trees develops a brown to black discolouration (Mayfield et al., 2008c).
Laurel wilt is responsible for the death of hundreds of millions of redbay (Persea borbonia sensu lato) trees throughout the southeastern USA, and the disease is also having significant effects on other species such as sassafras (Sassafras albidum) in natural ecosystems and avocado (Persea americana) in commercial production areas of south Florida. Laurel wilt is caused by the pathogen Raffaelea lauricola, a fungal symbiont of the redbay ambrosia beetle, Xyleborus glabratus. Thus far, the disease is confined to members of the Lauraceae that are native to the USA, or native to such places as the Caribbean, Central America and Europe and grown in the USA. The beetle and fungus are native to Asia and were likely introduced with untreated solid wood packing material at Port Wentworth, Georgia in the early 2000s. Since that time laurel wilt has spread rapidly in the coastal plains of the southeastern USA, spreading north into central North Carolina, as far west as Texas, and reaching the southernmost counties of Florida. Current models suggest that X. glabratus can tolerate temperature conditions that occur throughout much of the eastern USA, and so the disease threatens sassafras throughout much of this region. The disease poses a threat to lauraceous species indigenous to other areas of the Americas as well as Europe and Africa.
Many members of the Lauraceae that are native to the southeastern USA appear to be highly susceptible to laurel wilt, although some have not been greatly impacted by the wilt for various reasons. A couple of species in the Lauraceae that are native to Florida appear to be somewhat resistant to the disease. Species indigenous to South East Asia appear to be mostly resistant to laurel wilt. A more complete assessment of what is known about the susceptibility of the individual species follows.
Persea borbonia (redbay) and P. palustris (swampbay) are very similar taxa with differentiating characteristics that are vague and not always reliable (Coker and Toten, 1945). Some have regarded the two taxa as the same species or varieties of a species (Radford et al., 1968;Little, 1979) while others consider them to be separate species (Shearman et al., 2018;Weakley 2015). Regardless, redbay and swampbay, historically treated by many as one species (Radford et al., 1968;Brendemuehl, 1990), appear to be equally susceptible to laurel wilt (Fraedrich et al., 2008), and are difficult to accurately distinguish under field conditions. Thus, redbay is treated in this database as a single species (i.e. P. borbonia sensu lato). Redbays are evergreen trees that occur in the coastal plain forests of the southeastern USA, and are a minor use hardwood and ecologically important in the forest ecosystems where they occur (Brendemuehl, 1990). Redbay has been affected by laurel wilt throughout much of its range with losses that are estimated into the hundreds of millions of trees (Hughes et al., 2017). The disease preferentially affects larger diameter trees (Fraedrich et al., 2008;Mayfield and Brownie, 2013) and throughout its range there is still high survivorship among smaller diameter redbay trees as well as sapling and seedlings (Cameron et al., 2015). The reason for this phenomenon is thought to be due to the preference of X. glabratus to attack larger diameter trees (Mayfield and Brownie, 2013) and not due to resistance in the smaller diameter plants (Fraedrich et al., 2008). Thus, although redbay trees have been devastated by laurel wilt in the southeastern USA, it does not appear that the species is in imminent danger of extinction. The long term survival of redbay in the southeastern USA will depend on the ability of X. glabratus to find and reproduce in smaller diameter redbays or other suitable hosts.
Sassafras albidum (sassafras) is a deciduous tree species that occurs in various forest types over much of the eastern half of the USA (Griggs, 1990;Randolph, 2017) and is a minor use hardwood (Harding et al., 1997;Cassen, 2007). Pathogenicity tests confirmed that sassafras is highly susceptible to laurel wilt (Fraedrich et al., 2008) and the disease has affected sassafras across the southeastern USA (Bates et al., 2013;Fraedrich et al., 2015a, Olatinwo et al., 2016). Recent studies indicate that X. glabratus can survive the low winter temperatures throughout much of the range of sassafras (Formby et al., 2018), however at this time, the northern most location of the disease is central North Carolina (Mayfield et al., 2019).
Persea americana (avocado) is a tropical evergreen tree that is native to Central America and the Caribbean. The species is cultivated for production of avocados in Florida and California in the USA, and is also grown in Mexico and many other countries. Three distinct races of avocado are recognized that include the Mexican, Guatemalan and West Indian. The West Indian and West Indian-Guatemalan hybrids are primarily cultivated for commercial production in Florida (Mayfield et al., 2008a). Some avocado cultivars are more susceptible to laurel wilt than others, and West Indian cultivars such as ‘Simmonds’ appear to be highly susceptible (Mayfield et al., 2008a;Ploetz et al., 2012a). The ‘Simmonds’ cultivar comprises approximately 35% of the avocado production in Florida (Ploetz et al., 2011b). The West Indian-Guatemalan hybrids are generally susceptible but less so than the West Indian cultivars, and Guatemalan x Mexican hybrids such as the ‘Hass’ cultivar appear to be among the most resistant (Mayfield et al., 2008a;Ploetz et al., 2012a). The ‘Hass’ cultivar accounts for 95% of all production in California (Ploetz et al., 2017a).
Persea humilus (silk bay) is another species for which the taxonomy is confused. Some would regard silk bay as a species (Nelson, 1994), while others regard this taxon as a variety of redbay (Persea borbonia var. humilus) (Wunderlin, 1998). Silk bay is a small evergreen tree that is native to the scrub forests of central Florida. Laurel wilt is currently affecting silk bay in forests, and its susceptibility to the disease has been confirmed through pathogenicity tests (Hughes et al., 2012).
Lindera melissifolia (pondberry) is a small, deciduous, clonal shrub that is extremely rare and listed as an endangered species in the USA. Pathogenicity tests have determined that pondberry is highly susceptible to laurel wilt, but the disease has only been observed once in this species under natural conditions (Fraedrich et al., 2011). Because of its small stem diameter, pondberry is not readily attacked by X. glabratus. However, because of the clonal nature of this species, when infections occur, the disease can spread rapidly through rhizomes and kill multiple ramets within a population (Best and Fraedrich, 2018).
Lindera benzoin (spicebush) is a common small, deciduous shrub species that is found in the southeastern USA, and in pathogenicity tests it proved to be highly susceptible to laurel wilt (Fraedrich et al., 2008). The disease has been documented only once naturally in spicebush (Fraedrich et al., 2016), and because of the small diameter of spicebush, it is not readily attacked by X. glabratus. Therefore, the disease does not appear to be a major threat to this species.
Litsea aestivalis (pondspice) is a relatively large (0.5-3 m tall) deciduous, multi-branched shrub that occurs in the southeastern USA. The species is rare and is listed as threatened. Pondspice is highly susceptible to laurel wilt (Fraedrich et al., 2011), but due to the small size of this species, it is not readily attacked by X. glabratus. Laurel wilt has been observed in pondspice in Georgia and South Carolina (Fraedrich et al., 2011) and Florida (Hughes et al., 2011).
Licaria trianda (pepperleaf sweetwood) is a rare, evergreen tree native to the lower, southeastern portion of Florida. The species is considered to be endangered. A pathogenicity study determined that pepperleaf sweetwood was susceptible to disease caused by R. lauricola. Leaves of infected seedlings developed chlorosis and abscised, and a brown discolouration was noted in the xylem of stems. However, seedlings did not die from the disease (Ploetz and Konkol, 2013).
Ocotea coriacea (lancewood) is a small, evergreen tree that is found at scattered locations in central to south Florida and elsewhere in Central America and the Caribbean. Saplings inoculated with R. lauricola develop discolouration in the xylem and occasionally dieback of the branches but saplings do not die (S Fraedrich, US Forest Service, Georgia, USA, unpublished data).
Umbellularia californica (California laurel) is a large evergreen tree species native to southwestern Oregon, and the Coastal Ranges and Sierra Nevada of California. In laboratory pathogenicity tests, R. lauricola -inoculated plants developed sapwood discolouration and branch dieback but plants did not die from wilt (Fraedrich, 2008). A subsequent study also found that California laurel was an excellent brood host for X. glabratus (Mayfield et al., 2013).
Laurus nobilus (bay laurel) is an evergreen tree or large shrub species that is native to the Mediterranean regions of Europe, Asia and Africa. The taxonomy of Laurus nobilis and a similar species, L. azorica, which is found in Madeira and the Canary Islands, is confused and in need of review (Arroyo-García et al., 2001). Laurus nobilus was introduced into the USA, where it has been cultivated as a culinary herb and valued as a landscape ornamental species. Laurel wilt has been observed in a landscape plant in Florida and susceptibility of the bay laurel to the disease was subsequently confirmed in pathogenicity tests (Hughes et al., 2014).
Persea indica (viñatigo) is an evergreen tree native to the maritime forests of the Canary Islands, Madeira and the Azores. Viñatigo has been used as an ornamental in Florida and California in the USA (Schuch et al., 1992), and the species has been shown to be susceptible to laurel wilt in field and laboratory experiments (Hughes et al., 2013).
Cinnamomum camphora (camphortree) is indigenous to China, Japan, Taiwan and other countries in eastern Asia. The species was introduced into the southeastern USA in the 1800s and was used for camphor production, but has escaped cultivation and is now naturalized in some forest types (Langeland et al., 2008). Camphortree appears to be highly resistant to laurel wilt. Reports of laurel wilt in camphortree are not known in Asia, and in the USA the disease rarely affects camphortree in areas where redbay populations have been decimated by laurel wilt. Dieback in camphortrees is occasionally observed in trees where laurel wilt is prevalent on redbay, and R. lauricola has been recovered from such trees (Smith et al., 2009;Fraedrich et al., 2015b). Single point inoculations of camphortree saplings with R. lauricola do not produce symptoms of laurel wilt or dieback under controlled conditions;however, multiple inoculations with R. lauricola have resulted in top dieback and mortality in saplings (Fraedrich et al., 2015b).
In addition, a study of the susceptibility of lauraceous species native to South East Asia, indicated that Cinnamomum osmophloeum, C. jensenianum, Machilus zuihoensis and M. thunbergii were also much more resistant to laurel wilt than species native to North America (Shih et al., 2018).
Eggs;Eggs are pear shaped with a pedicel spike at the base, approximately 0.2 mm long.;Puparium;A flat, irregular oval shape, about 0.7 mm long, with an elongate, triangular vasiform orifice. On a smooth leaf the puparium lacks enlarged dorsal setae, but if the leaf is hairy, 2-8 long, dorsal setae are present.;Adult;Adults are approximately 1 mm long, the male slightly smaller than the female. The body and both pairs of wings are covered with a powdery, waxy secretion, white to slightly yellowish in colour.
Early indication of infestation may consist of chlorotic spots caused by larval feeding, which may also be disfigured by honeydew and associated sooty moulds. Leaf curling, yellowing, mosaics or yellow-veining may also indicate the presence of whitefly-transmitted viruses. These symptoms are also observed in B. tabaci infestations, however phytotoxic responses such as a severe silvering of courgette and melon leaves, mis-ripening of tomato fruits, stem whitening of brassicas and yellow veining of some solanaceous plants may also be seen (Costa et al., 1993, Secker et al., 1998).;The feeding of adults and nymphs causes chlorotic spots to appear on the surface of the leaves. Depending on the level of infestation, these spots may coalesce until the whole of the leaf is yellow, apart from the area immediately around the veins. Such leaves are later shed. The honeydew produced by the feeding of the nymphs covers the underside of leaves and can cause a reduction in photosynthetic potential when colonized by moulds. Honeydew can also disfigure flowers and, in cotton, can cause problems in lint processing. Following heavy infestations, plant height, the number of internodes, and yield quality and quantity can be affected, for example, in cotton.;Phytotoxic responses in many plant and crop species caused by larval feeding include severe silvering of courgette leaves, white stems in pumpkin, white streaking in leafy Brassica crops, uneven ripening of tomato fruits, reduced growth, yellowing and stem blanching in lettuce and kai choy (Brassica campestris) and yellow veining in carrots and honeysuckle (Lonicera) (Bedford et al., 1994a,b).;A close observation of leaf undersides will show tiny, yellow to white larval scales. In severe infestations, when the plant is shaken, numerous small and white adult whiteflies will emerge in a cloud and quickly resettle. These symptoms do not appreciably differ from those of Trialeurodes vaporariorum, the glasshouse whitefly, which is common throughout Europe.
The development of transgenic resistant plant and crop species through genetic engineering must be considered and accepted as a future method of control where whitefly-transmitted viruses are already endemic and causing severe crop losses (Wilson, 1993, Raman and Altman, 1994). Traditional sources of resistance have been used successfully for the control of other whitefly species.
C. arvensis is a herbaceous perennial growing from a very deep root system. Shoots develop from adventitious buds on the deep root system at almost any depth down to 1 m. Above ground, the stems trail or climb by twining. Stems slender, to 1.5 m long, twining anticlockwise, glabrous or finely pubescent. Leaves alternate, petiolate, variable in shape, lanceolate or ovate to narrow-oblong, 1.2-5.0 cm long, acute at the apex, entire but often hastate-sagittate at the base, glabrous or pubescent with scattered crisped hairs. Flowers axillary, solitary or in cymes 2-3 on peduncles subequal to the subtending leaf;bracteoles linear, 2-4 mm long. Sepals free, obtuse, 2.5-4.5 mm long. Corolla funnel-shaped, pentamerous with 5 radial pubescent bands but not divided into distinct lobes, 10-25 mm long, 10-25 mm diameter, white or pink. Stamens 5, inserted on corolla tube. Style single with two oblong stigmas. Ovary two-celled. Fruit a capsule, globular to ovoid with a persistent style base, breaking open irregularly. Seeds usually 4, compressed-globose, 3-5 mm diameter;testa granular, dark-brown or black.
C. arvensis, commonly known as bindweed, is a climbing herbaceous perennial native to Eurasia. This species is present in most parts of the world where it has been accidentally introduced as a contaminant of both agricultural and horticultural seed. C. arvensis produces a long lived root system and up to 500 seeds per plant. This species can grow very rapidly where it competes with native vegetation and agricultural and horticultural crops for nutrients, moisture, light and space. As a result, neighbouring plants may become smothered leading to a decrease in biodiversity and a reduction in crop yield. Control of this species is difficult due to the longevity of seeds in the soil bank (up to 20 years) and the ability of small fragments of rhizome to produce new shoots.
Annual crops such as cereals and grain legumes are particularly susceptible, and it is also widely reported as a troublesome weed in vineyards. Holm et al. (1977) also list C. arvensis as a weed of sugarbeet, cotton, tobacco, tea, potato, orchards, pineapples, vegetables, flax and lucerne.
The initial leaves of seedling E. crassipes are elongated and strap-like, but soon develop the familiar spathulate form and, under suitable unshaded conditions, swollen petioles which ensure that, once dislodged, the seedlings will float from the mud into open water. The plant is very variable in size, seedlings having leaves that are only a few centimetres across or high, whereas mature plants with good nutrient supply may reach 1 m in height. Plants in an uncrowded situation tend to have short, spreading petioles with pronounced swelling, while in a dense stand they are taller, more erect and with little or no swelling of the petioles.
The plant system consists of individual shoots/crowns each with up to ten expanded leaves arranged spirally (3/8 phyllotaxy) and separated by very short internodes. As individual shoots develop, the older leaves die off leaving a stub of leafless dead shoot projecting downwards. This may eventually cause the whole shoot to sink and die.
Leaves consist of petiole (often swollen, 2-5 cm thick) and blade (roughly round, ovoid or kidney-shaped, up to 15 cm across). The base of the petiole and any subsequent leaf is enclosed in a stipule up to 6 cm long.
Roots develop at the base of each leaf and form a dense mass: usually 20-60 cm long, though they can extend to 300 cm. The ratio of root to shoot depends on the nutrient conditions, and in low nutrient conditions they may account for over 60% of the total plant weight. They are white when formed in total darkness but often purplish under field conditions, especially in conditions of low nutrients.
Periodically, axillary buds develop as stolons, growing horizontally for 10-50 cm before establishing daughter plants. Extremely large populations of inter-connected shoots can develop very rapidly, though the connecting stolons eventually die.
The inflorescence is a spike which develops from the apical meristem, but tends to appear lateral owing to the immediate development of an axillary bud as a 'renewal' or 'continuation' shoot. Each spike, up to 50 cm high, is subtended at the base by two bracts and has 8-15 sessile flowers (rarely 4-35). Each flower has a perianth tube 1.5 cm long, expanding into six mauve or purple lobes up to 4 cm long. The main lobe has a bright-yellow, diamond-shaped patch surrounded by deeper purple. Once the inflorescence is fully emerged from the leaf sheath, flowers all open together, starting at night, completing the process in the morning and withering by the next night when the peduncle starts to bend down. Each capsule may contain up to 450 small seeds, each about 1 x 3 mm.
The flowers are tristylous. They have six stamens and one style, arranged in three possible configurations (floral trimorphism) - with short style (and medium and long stamens), medium style (short and long stamens) or long style (short and medium stamens). The medium style form is genetically dominant and is by far the commonest form in almost all infested areas. The short-styled form is only known from South America, whereas the long-styled form is found commonly in South America, more rarely in South-East Asia and very rarely in Africa. Only in Sri Lanka is the long-styled the commonest form. Some other tristylous species show incompatibility between the different forms but E. crassipes does not. Hence pollination (mainly by wind) can result in good seed set, though in some populations there may be a higher degree of self-incompatibility.
Detection of mature floating E. crassipes plants is all too simple but where control methods have been used to eliminate these, there is a need to watch for seedling plants at the edges of the water body.
E. crassipes, a native of South America, is a major freshwater weed in most of the frost-free regions of the world and is generally regarded as the most troublesome aquatic plant (Holm et al., 1997). It has been widely planted as a water ornamental around the world because of its striking flowers. Wherever it has encountered suitable environmental conditions it has spread with phenomenal rapidity to form vast monotypic stands in lakes, rivers and rice paddy fields. Then it adversely affects human activities (fishing, water transport) and biodiversity. It is impossible to eradicate, and often only an integrated management strategy, inclusive of biological control, can provide a long-term solution to this pest.
Fusarium wilt of bananas is caused by F. oxysporum f.sp. cubense, a common soil inhabitant. Other formae speciales attack a wide variety of other crops, including cotton, flax, tomatoes, cabbages, peas, sweet potatoes, watermelons and oil palms.;The formae speciales of Fusarium oxysporum each produce three types of asexual spores. The macroconidia (22-36 x 4-5 µm, see Wardlaw, 1961 for measurements) are produced most frequently on branched conidiophores in sporodochia on the surface of infected plant parts or in artificial culture. Macroconidia may also be produced singly in the aerial mycelium, especially in culture. The macroconidia are thin-walled with a definite foot cell and a pointed apical cell. Oval or kidney-shaped microconidia (5-7 x 2.5-3 µm) occur on short microconidiophores in the aerial mycelium and are produced in false heads. Both macroconidia and microconidia may also be formed in the xylem vessel elements of infected host plants, but the microconidia are usually more common. The fungus may be spread by macroconidia, microconidia and mycelium within the plant as well as outside the plant. Illustrations of the conidia have been published (Nelson et al., 1983).;Chlamydospores (9 x 7 µm) are thick-walled asexual spores that are usually produced singly in macroconidia or are intercalary or terminal in the hyphae. The contents are highly refractive. Chlamydospores form in dead host-plant tissue in the final stages of wilt development and also in culture. These spores can survive for an extended time in plant debris in soil.;Mutation in culture is a major problem for those working with vascular wilt isolates of F. oxysporum. The sporodochial type often mutates to a 'mycelial' type or to a 'pionnotal' type. The former has abundant aerial mycelium, but few macroconidia, whereas the latter produces little or no aerial mycelium, but abundant macroconidia. These cultures may lose virulence and the ability to produce toxins. Mutants occur more frequently if the fungus is grown on a medium that is rich in carbohydrates.
Banana;The various symptoms of Fusarium wilt on banana are described and well illustrated by Ploetz and Pegg (1999).;The first external symptoms of Fusarium wilt on bananas is a faint off-green to pale-yellow streak or patch at the base of the petiole of one of the two oldest leaves. The disease can then progress in different ways. The older leaves can yellow, beginning with patches at the leaf margin. Yellowing progresses from the older to the younger leaves until only the recently unfurled or partially unfurled centre leaf remains erect and green. This process may take from 1 to 3 weeks in cultivar 'Gros Michel'. Often the yellow leaves remain erect for 1-2 weeks or some may collapse at the petiole and hang down the pseudostem. In contrast to this 'yellow syndrome', leaves may remain completely green except for a petiole streak or patch but collapse as a result of buckling of the petiole. The leaves fall, the oldest first, until they hang about the plant like a skirt. Eventually, all leaves on infected plants fall down and dry up. The youngest are the last to fall and often stand unusually erect.;Splitting of the base of the pseudostem is another symptom as is necrosis of the emerging heart leaf. Other symptoms include irregular, pale margins on new leaves and the wrinkling and distortion of the lamina. Internodes may also shorten (Stover, 1962, 1972, Jones, 1994, Moore et al., 1995).;The characteristic internal symptom of Fusarium wilt is vascular discoloration. This varies from one or two strands in the oldest and outermost pseudostem leaf sheaths in the early stages of disease to heavy discoloration throughout the pseudostem and fruit stalk in the later disease stages. Discoloration varies from pale yellow in the early stages to dark red or almost black in later stages. The discoloration is most pronounced in the rhizome in the area of dense vascularization where the stele joins the cortex. When symptoms first appear, a small or large portion of the rhizome may be infected. Eventually, almost the entire differentiated vascular system is invaded. The infection may or may not pass into young budding suckers or mature 'daughter' suckers. Where it does, discoloration of vascular strands may be visible in the excised sucker. Usually, suckers less than 1.5 m tall and ca. 4 months old do not show external symptoms. Where wilt is epidemic and spreading rapidly, suckers are usually infected and seldom grow to produce fruit. Above- and below-ground parts of affected plants eventually rot and die.;Fusarium wilt was reported to occur on banana cultivars of the 'Mutika-Lujugira' (AAA genome) subgroup in East Africa above 1400 m. Internal symptoms were much less extensive than those described above and external symptoms more subtle, comprising thin pseudostems and small fingers. Nevertheless, symptomatic plants were recognized by smallholders and were rogued. These mild symptoms were initially believed to be indicative of an attack on a plant whose defences have been weakened as a result of cooler conditions or other predisposing factors at altitude (Ploetz et al., 1994). Given the importance of this banana group, also referred to locally as ÔEast African highland bananasÕ, to local trade and as a staple food, further investigation was merited. This revealed that the disorder also affected non-indigenous banana types, including Cavendish and Bluggoe (which were not affected by Fusarium wilt) and was related to abnormal soil nutrient levels and farm management practice. Discoloration similar to that caused by F. oxysporum f.sp. cubense was observed in vascular tissues of affected plants. Fusarium pallidoroseum (syn. Fusarium semitectum) was consistently isolated from such tissues but found to be non-pathogenic. F. oxysporum was not recovered (Kangire and Rutherford, 2001, Rutherford, 2006).
F. oxysporum f.sp. cubense is one of around 100 formae speciales (special forms) of F. oxysporum which cause vascular wilts of flowering plants (Gerlach and Nirenberg, 1982). Hosts of the various formae speciales are usually restricted to a limited and related set of taxa. As currently defined, F. oxysporum f.sp. cubense affects the following species in the order Zingiberales: in the family Musaceae, Musa acuminata, M. balbisiana, M. schizocarpa and M. textilis, and in the family Heliconeaceae, Heliconia caribaea, H. chartacea, H. crassa, H. collinsiana, H. latispatha, H. mariae, H. rostrata and H. vellerigera (Stover, 1962, Waite, 1963). Additional hosts include hybrids between M. acuminata and M. balbisiana, and M. acuminata and M. schizocarpa.;F. oxysporum f.sp. cubense may survive as a parasite of non-host weed species. Three species of grass (Paspalum fasciculatum, Panicum purpurascens [ Brachiaria mutica ] and Ixophorus unisetus) and Commelina diffusa have been implicated (Waite and Dunlap, 1953).
Clypeus amphigenous, developing in epidermis, generally circular, 0.5-2.0 mm diameter, dark-brown to black, glossy. Ascomata perithecial subglobose, ostiolate, aggregated or scattered, subepidermal beneath clypeus, 170-350 µm diameter. Paraphyses numerous, filiform, longer than asci, to 125 µm. Asci narrowly cylindrical, 8-10 x 80-100 µm, pedicel short. Ascospores uniseriate in ascus, hyaline, aseptate, broadly ellipsoid, 5.5-8.5 x (8-)10-14 µm (often 13-14 µm). Conidiomata pycnidial, subepidermal beneath clypeus, often in younger lesions. Conidiophores branched at two or three levels, branches tapering, 11-16 x 1.0-1.5 µm. Conidia filiform, hyaline, 10-15 x 0.5 µm, gradually tapering to apex. For additional descriptions see Dalby (1917), Orton (1944), Parbery (1967), and Liu (1973).
Lower leaves should be examined for small, raised, glossy, dark, circular, or oval to irregular, spots, or for brown lesions, often with a dark border, having a dark ascomata at the centres (CIMMYT, 2003).
Initial symptoms are small, yellow-brown spots on either side of the leaf. The raised glossy black clypeus covering the ascomata, surrounded by a narrow chlorotic border, develops in the spot. Spots are circular, oval, sometimes angular or irregular, and may coalesce to form stripes up to 10 mm long (Liu, 1973).
Some spots enlarge around the ascomata, with an initially water-soaked area becoming necrotic, to form circular-oval brown lesions 3-8 mm diameter with a dark outer edge (Bajet et al., 1994);this is called the “fish-eye” symptom (Hock et al., 1992). These larger lesions coalesce after 7-14 days;areas between spots become water-soaked and dry out. When conditions favour disease, leaves may be fully dead in 21-30 days. The fungus spreads from the lowest leaves to upper leaves, leaf sheathes and the husks of developing ears (Bajet et al., 1994).
As many as 4000 lesions may form on a leaf, and, in susceptible genotypes, 80% or more of the leaf area is affected, leaving little green tissue or killing the plant (Ceballos and Deutsch, 1992). Affected ears have reduced weight and loose kernels, and kernels at the ear tip may germinate prematurely (CIMMYT, 2003).
P. maydis, a perithecial ascomycete, causes a tar spot disease of maize that is usually a minor problem. More significant damage to leaves and yield is caused by the fungus Monographella maydis whose infection follows that of the tar-spot fungus, at least where studied in Mexico (Hock et al., 1992;1995). The source of initial inoculum for both fungi is not determined. The disease they cause occurs in the cooler and higher elevations of Mexico, and Central and South America, and the West Indies, so their ability to spread over land through other climatic zones may be limited. Not known to be seedborne or to infect other species, P. maydis could be transported on fresh or dry maize leaves or husks, or products made from them, from which ascospores would have to be produced and carried by wind or rain splash to maize [ Zea mays ].
P. maydis is restricted to Zea mays (maize) (Parbery, 1967), and was not found on other grasses, including other Zea species, in Mexico (Hock et al., 1995).
The following taxonomic description of R. ferrugineus was provided by Booth et al. (1990).
"Ferrugineous to black, legs paler, elytra shining or dull, slightly pubescent, black spots on pronotum extremely variable. Antennal insertions subbasal, scrobes deep, broad and widely opened ventrally, scape longer than funicle and club combined, equal to half length of rostrum, with funicular segments thick, conical, club large, broadly triangular, usually ferrugineous with 8 to 15 setae on inner side of spongy area. Rostrum in males almost four fifths length of pronotum. In females longer, slender, more cyclindrical;straight in profile, broad at base, apex not grooved, with dense, erect setae, at least subapically in males only, but not reaching scrobes, dorsal surface variously sculptured, ventrally very finely punctured, ventral space between antennal scrobes strongly narrowing posteriorly, gular suture with elongate-oval shape before narrowing to base. Submentum truncately concave with narrowly elongate, median depression, extending throughout its length. Mandibles tridentate distally, all teeth sharply pointed, apical and subapical teeth widely separated. Frons narrower than rostrum at base. Pronotum abruptly constricted anterolateraly, posterior margin broadly rounded. Scutellum one-quarter to one fifth elytral length, somewhat pointed posteriorly. Elytra smooth or with slight velvety pubescence, punctures along outer edges, with five deep striae and traces of four laterally. Procoxae strongly globose, widely separated, mesocoxae covered with soft, reddish-brown setae, pro- and mesofemora not strongly curved ventrally, with setae on ventral side of profemora in males only, tarsi pseudotetramerous, first segment twice as long as second, third with broad, median patch and lateral row of reddish-brown setae, fifth segment as long as first four combined, with nine to twelve setae ventrally. First abdominal sternite as long as third and fourth combined, but much shorter than second, sparsely punctures medially, strongly punctures laterally, fifth segment strongly punctured dorsolaterally, pygidium sparsely and minutely punctured posteriorly and dorsolaterally."
Eggs are creamy white, oblong and shiny. The average size of an egg is 2.62 mm long and 1.12 mm wide (Menon and Pandalai, 1960). Eggs hatch in 3 days and increase in size before hatching (Reginald, 1973). The brown mouth parts of the larvae can be seen through the shell before eclosion.
The larvae can grow up to 35 mm long and can be recognised by the brown head and white body. The body is composed of 13 segments. Mouthparts are well developed and strongly chitinized. The average length of fully grown larvae is 50 mm and the mean width is 20 mm in the middle.
When about to pupate, larvae construct an oval-shaped cocoon of fibre (Menon and Pandalai, 1960). The pupal case can range in length from 50-95 mm and in width from 25-40 mm. The prepupal stage lasts for about 3 days and the pupal period varies from 12-20 days. Pupae are first cream coloured but later turn brown. The surface is shiny, but greatly furrowed and reticulated. The average length of pupae is 35 mm and the average width is 15 mm.
Adult weevils are reddish brown, about 35 mm long and 10 mm wide and are characterized by a long curved rostrum (snout). Dark spots are visible on the upper side of the middle part of the body. The head and rostrum comprise about one-third of the total length. In the male, the dorsal apical half of the snout is covered by a patch of short brownish hairs, the snout is bare in the female, more slender, curved and a little longer than the male (Menon and Pandalai, 1960).
Crawlers are 0.3 mm long. Immature and newly matured females have yellowish bodies dusted with mealy white wax that is often thinner between the segments, giving the body a slightly barred appearance. Short, waxy filaments develop around the margin in the adult female, each less than a quarter as long as the body. The adult female is 2.0-3.5 mm long, soft-bodied, elongate oval and slightly flattened;on maturation she begins to secrete sticky, elastic, white wax filaments from the edges of her abdomen to form a protective ovisac for her yellow eggs. The ovisac can be as much as twice as long as the body, or more (Miller et al., 1999). Sometimes the body colour of the mature female is not immediately apparent if she has become buried under white ovisac material. The male is a short-lived, small insect with long, segmented antennae;six legs each bearing a single claw;one pair of simple wings coated with white wax powder;a pair of long, white waxy filaments at the posterior of the abdomen;and no mouthparts. Live specimens have yellow body contents;within 24 hours of death, the body contents characteristically darken to grey or black.
Heavy infestations by P. marginatus cause stunting and deformation of new growth, leaf yellowing, leaf curl and early fruit drop (Anon., 2000). Fruit may become completely covered by a layer of mealybugs and wax secretions (Miller et al., 1999), and papaya fruit tissue underneath the mealybug colonies becomes hard and bitter. Papaya, hibiscus and annona species are particularly badly affected.
Paracoccus marginatus is a mealybug native to Central America. It has been spread accidentally outside its native range by trade in live plant material, such as papaya fruits. It became an invasive pest in the Caribbean Islands and USA (Florida) in 1994-2002;the West and Central Pacific islands in 2002-2006;South-East Asia and the Indo-Pacific islands in 2008-2010;West Africa in 2010-2016;East Africa from 2015;and Israel in 2016. The pest is expected to continue spreading, and climate warming is likely to increase the areas where it can establish. It is is polyphagous and spreads rapidly, forming heavy infestations on aerial plant parts and killing some host-plants, including papaya. It poses a threat to commercial papaya plantations.
The species was described from material collected on cassava and papaya, but P. marginatus is now recognized to be highly polyphagous, attacking vegetables and fruits as well as ornamental plants belonging to 136 genera in 49 plant families (García Morales et al., 2019). It causes significant damage to cassava in Central America. Papaya, hibiscus and annona species are particularly badly affected (Matile-Ferrero et al., 2001). Papaya is a preferred host.
Eggs - elliptical or ovoid in shape, milky-white and shiny when first laid, 0.5-0.8 mm long, 0.25-0.35 mm wide (Bergamin, 1943;Hernandez-Paz and Sanchez de Leon, 1978;Johanneson, 1984).
H. hampei can be detected in the trees and coffee beans.
Tree - inspect the berries and look for a small cylindrical perforation. Look at the lower branches and fallen berries as these may be more likely to be infested. There are numerous sampling methods, many based on counting all berries on 30 or more branches over a hectare and evaluating percentage attack. As yet there is no easy or universal way to relate level of crop attack to future loss at harvest. A figure of 5% infested berries is often used as an economic threshold for field control activities, but more study on this is needed.
Coffee beans - as the perforation on berries may be difficult to see, rub suspect beans between the hands to remove the parchment and look for the perforation. Often a small indentation will be present where the borer started to attack but failed to establish itself.
A trap based on ethanol and methanol has been developed but it also catches many other scolytids. It is useful to monitor emergence flight activity, most notably when rains follow a dry period. French research has renewed interest in trapping as a form of control, initial results have been are encouraging though more research needs to be done to confirm the economic viability of this method (Dufour et al., 1999). Fernandes et al. (2014) found that mass trapping could reduce attacks, but not below an economic threshold.
Attack by H. hampei begins at the apex of the coffee berry from about eight weeks after flowering. A small perforation about 1 mm diameter is often clearly visible though this may become partly obscured by subsequent growth of the berry or by fungi that attack the borer. During active boring by the adult female, she pushes out the debris, which forms a deposit over the hole. This deposit may be brown, grey or green in colour.
Infestation is confirmed by cutting open the berry. If the endosperm is still watery, the female will be found in the mesoderm between the two seeds, waiting for the internal tissues to become more solid. If the endosperm is more developed, the borer will normally be found there amongst the excavations and irregular galleries that it has made. The borer sometimes causes the unripe endosperm to rot, most commonly by species Erwinia, causing it to turn black (Sponagel, 1994) and the borer to abandon the berry.
H. hampei, otherwise known as the coffee berry borer, is the most serious pest of coffee in many of the major coffee-producing countries in the world. The scolytid beetle feeds on the cotyledons and has been known to attack 100% of berries in a heavy infestation. Crop losses can be very severe and coffee quality from damaged berries is poor. H. hampei has been transported around the world as a contaminant of coffee seed and very few coffee-producing countries are free from the borer. Its presence in Hawaii was confirmed in 2010 and Papua New Guinea and Nepal remain free of the pest: in Papua New Guinea an incursion prevention programme was mounted in 2007 (ACIAR, 2013) to reduce chances of invasion from Papua Province (Indonesia). There is no simple and cheap method of control of H. hamepi.
H. hampei is sometimes reported attacking and breeding in plants other than coffee, however there are few convincing published studies of this with supporting expert taxonomic identification. However, a Colombian study (L Ruiz, Cenicafé, Centro Nacional de Investigaciones de Café, Colombia, personal communication, 1994) reports rearing the borer through to adulthood on seeds of Melicocca bijuga and a Guatemalan study (O Campos, Anacafé, Asociacion Nacional del Café, Guatemala, personal communication, 1984) reports the same for Cajanus cajan. Vega et al. (2012) reviewing older little-known literature including that of Schedl (1960), make the case that the African host range may be broader than previously suspected. As there is much current interest in mass production of the borer, further studies of alternative food sources would be of interest. Nevertheless, all field studies of the borer suggest that coffee is the only primary host and that population fluctuations are hence due almost entirely to its interaction with coffee and not to the presence of alternative hosts.
Chevalier (cited in Le Pelley, 1968) found Coffea liberica almost immune to H. hampei followed by C. excelsa, C. dewerei, C. canephora and C. arabica in increasing order of attractiveness to the borer. Villagran (1991) found that. H. hampei had difficulty in penetrating the hard exterior of C. liberica berries. However, Roepke (in Le Pelley, 1968) states that C. liberica is preferentially attacked. Extensive studies by Kock (1973) reported C. canephora variety Kouilou (or Quoillou) is attacked less than the Robusta variety.
Villagran (1991) found C. kapakata supporting very significantly fewer immature stages of the borer than other varieties and some tendency for C. arabica variety Mundo Novo also to support fewer progeny. Olfactometry tests by Duarte (1992) showed C. kapakata to be significantly less attractive. C. kapakata appears to be one of the most resistant coffee species currently known but this is not a commercial variety and neither the berries nor the plant resemble a coffee plant to the casual observer.
Romero and Cortina-Guererro (2004) in laboratory studies in Colombia found no difference in levels of antixenosis (deterrence to attack coffee in field tests) of various coffee varieties (including C. arabica Caturra, various Ethiopian accessions as well as C. liberica). However Romero and Cortina-Guererro (2007) did find differences in antibiosis (expressed as fecundity) with Ethiopian accession CC532 and C. liberica both yielding significantly fewer borer progeny.
Gongora et al. (2012) confirmed the inhibitory effects of C. liberica through a functional genomics study using ESTs libraries, cDNA microarrays and an oligoarray containing 43,800 coffee sequences. The results allowed for a comparison of C. liberica vs. C. arabica berry responses to H. hampei infestation after 48 h. Out of a set of 2500 plant sequences that exhibited differential expression under H. hampei attack, twice the number were induced in C. liberica, than in C. arabica. One of the identified biochemical pathways was the one that leads to the production of isoprene. The authors studied the effect of isoprene on H. hampei by monitoring the development of the insect from egg to adult, using coffee-artificial diets amended with increasing concentrations of isoprene. Concentrations of isoprene above 25 ppm caused mortality and developmental delay in all insect stages from larva to adult, as well as the inhibition of larvae moulting.
Hence it seems certain that varying amounts of resistance or antibiosis to the borer exists within species of Coffea. Such resistance to attack or even moderate antibiosis is worthy of further study because an increase in development time and/or decrease in fecundity could have a pronounced effect on infestation levels. Conventional breeding to introduce such inhibition from outside the Arabica genome might be difficult however, hence genetic engineering may be increasingly considered in the future.
A team of CIRAD scientists were the first to succeed in producing a transgenic coffee plant with Bt resistance to leafminers but there is no information about its effect on H. hampei (Leroy et al., 2000). Scientists from Brazil and Colombia (Barbosa et al., 2010) transformed C. arabica by introducing an enzyme inhibitor from the common bean (Phaseolus vulgaris). Beans have evolved an amylase enzyme inhibitor (or ‘starch blocker’) to make them less palatable to attacking insects. They demonstrated that crude seed extracts from genetically transformed C. arabica plants expressing the α-amylase inhibitor-1 gene (α-AI1) under the control of the common bean P. vulgaris seed-specific promoter PHA-L, inhibited 88 % of H. hampei α-amylases during in vitro assays. Since then, offspring from these GM coffee plants have been cultivated under greenhouse conditions to study the heredity, stability and expression of the α-AI1 gene. Subsequently Albuquerque et al. (2015) carried out in vivo assays of H. hampei development in berries of the transformed plants. A 26-day assay showed that the lifecycle of H. hampei was still completed, though significantly fewer offspring developed than on non-transformed control beans. Other tests showed that gene expression occurred only in the endosperm tissue. Commercial interest in developing transgenic coffee resistant to pests and diseases is still low however and might meet considerable consumer resistance.
Theoretically it would be possible to develop a forecasting model to predict upsurges of H. hampei, because under some conditions, especially after a long dry spell with high temperatures, large populations develop on fallen berries which then emerge after early rains. This however would require regular field monitoring and dissections of sampled berries and the costs of mounting such an exercise are probably too high. However, even occasional and non-intensive monitoring of borer during the post-harvest dry season, could give field technicians a feel for the build-up of populations that could be translated into warnings to farmers in exceptional circumstances. Recent El Niño events which cause prolonged hot and dry conditions, almost invariably give rise to an upsurge in infestations.
Traps with a 1:1 ethanol + methanol lure can be used to trap flying borer. Numbers caught relate quite closely to nearby total populations (Mathieu et al., 1999) so could be used to monitor borer populations. However, the traps placed outside an infested plot catch very few insects, so the power of the trap is low. This means that its use to detect borer flying into a quarantined zone is questionable. For that purpose simply checking coffee trees for infestations is probably quicker, more sensitive and cheaper. This is probably also true for routine monitoring of borer populations. Traps are now used sometimes as part of an IPM control strategy, i.e. for control rather than monitoring (Dufour and Frérot, 2008). Spectacular catches have been achieved in El Salvador (Dufour et al., 2004) and were related to measured declines in infestation. However results can be very variable. Fernandes et al. (2014) deployed 900 traps in four coffee farms and achieved a 57% reduction infestation, but levels were still above an economic loss threshold. It seems likely that traps can be effective in specific conditions, when placed after early rains when borers are emerging and when there are few berries to compete for the traps’ attractiveness. However the proportion of borers trapped to total infestation levels is always low 5%) so it is questionable whether traps are cost effective, especially since they need regular servicing to replenish the lure, clear debris etc., something that most farmers are not good at. Hence the traps need to be evaluated for specific coffee-growing conditions and results weighed against costs of the traps, their regular servicing and farmers’ willingness to service them regularly.
O. acuta is a bisexual species with multiple generations annually. This species is distinguished by the morphology of the adult female. No descriptive information on the morphology of the immature or adult male stages exists at present . The live adult females are pink and covered with a white powdery, waxy secretion. The females are uniquely found enclosed within whitish resinous cells that are open at one end, from which their pygidia protrude. The cells are usually attached to the stem at the base of the needle.
The extraction of sap by the feeding mealybugs in the area of the fascicle may lead to excessive resin flow resulting in the needles turning brown and eventually dropping off (Xu et al., 1992, Pan et al., 1994, Sun et al., 1996). High populations of the mealybug can potentially cause malformed growth, loss of plant vigour, stunting, defoliation, reduced seed production, and potential death of the plant, if not treated. The mealybugs are often found in the pitch cells located on new growth needles or on a short section of the stem immediately below the buds in the southern USA. However, the mealybugs are found completely covering the needles and shoots on pine branches in China. Heavy populations of the loblolly pine mealybug have been reported to severely damage slash pine cones that result in them being smaller than normal, deformed or crescent-shaped, and a reduction in seed production results (Sun et al., 1996). Also, the production of vast amounts of honeydew serves as a substrate for the development of sooty mould that blackens the branches, stems, and needles. These weakened trees are susceptible to attacks by other insects.
P. clandestinum is a low-growing perennial grass which spreads by underground rhizomes and above-ground runners. In open situations, growth is mainly by horizontal extension of the robust runners. The runners are several mm thick, and have internodes at intervals of about 5 cm, each with a single leaf sheath and blade. The blade is bright green, 3-4 mm wide, very short;only a few cm long towards the tips of vigorous runners, but up to 15 cm long in more closed vegetation. Leaves may be glabrous or softly hairy. A tiller may or may not develop within the leaf sheath. The ligule is a short hairy rim 1-2 mm long. The inflorescences are very inconspicuous, being almost totally enclosed in leafy axillary branches, and only apparent as a result of styles or stamens protruding from their tips. The inflorescence has only 2-4 spikelets, each 1-2 cm long with 2 florets and a circle of short bristles at their base. Stigma up to 3 cm long and stamens on fine silvery filaments up to 5 cm. Seeds about 2 mm long. For further detail see Holm et al. (1977). Below ground, the rhizomes have similar morphology to the runners, but without expanded leaves, occurring at depths of 20-30 cm.
P. clandestinum is an aggressive perennial plant, spreading by rhizomes below ground, especially by long runners above ground, and it also sets seed. It is native to the highlands of eastern Africa but has been widely introduced elsewhere for forage and for soil conservation. In well managed situations it does not generally spread very far but it is highly tolerant of grazing and mowing and can steadily invade poorly managed plantations. It also readily invades natural vegetation with resultant loss of biodiversity. This has occurred in Australia, New Zealand, South Africa, Hawaii and the Galapagos. It is listed as a Federal Noxious Weed in the USA.
In addition to the crops listed, many other annual and perennial crops are affected, together with pasture, turf and forestry species.
A. fulica is distinctive in appearance and is readily identified by its large size and relatively long, narrow, conical shell. Reaching a length of up to 20 cm, the shell is more commonly in the size range 5-10 cm. The colour can be variable but is most commonly light brown, with alternating brown and cream bands on young snails and the upper whorls of larger specimens. The coloration becomes lighter towards the tip of the shell, which is almost white. There are from seven to nine spirally striate whorls with moderately impressed sutures. The shell aperture is ovate-lunate to round-lunate with a sharp, unreflected outer lip. The mantle is dark brown with rubbery skin. There are two pairs of tentacles on the head: a short lower pair and a large upper pair with round eyes situated at the tip. The mouth has a horned mandible, and a radula containing about 142 rows of teeth, with 129 teeth per row (Schotman, 1989;Salgado, 2010). Eggs are spherical to ellipsoidal in shape (4.5-5.5 mm in diameter) and are yellow to cream in colour.
A. fulica is a large and conspicuous crop pest which hides during the day. Surveys are best carried out at night using a flashlight. It is easily seen, and attacked plants exhibit extensive rasping and defoliation. Weight of numbers can break the stems of some species. Its presence can also be detected by signs of ribbon-like excrement, and slime trails on plants and buildings.
In garden plants and ornamentals of a number of varieties, and vegetables, all stages of development are eaten, leading to severe damage in those species that are most often attacked. However, cuttings and seedlings are the preferred food items, even of plants such as Artocarpus which are not attacked in the mature state. In these plants damage is caused by complete consumption or removal of bark. Young snails up to about 4 months feed almost exclusively on young shoots and succulent leaves. The papaya is one of the main fruits which is seriously damaged by A. fulica, largely as a result of its preference for fallen and decaying fruit.
In plants such as rice, which are not targets of A. fulica, sometimes sheer weight of numbers can result in broken stems. In general, physical destruction to the cover crop results in secondary damage to the main crop, which relies on the cover crop for manure, shade, soil and moisture retention and/or nitrogen restoration. This in turn can result in a reduction in the available nitrogen in the soil and consequently marked erosion in steeper areas.
The giant African land snail A. fulica is a fast-growing polyphagous plant pest that has been introduced from its native range in East Africa to many parts of the world as a commercial food source (for humans, fish and livestock) and as a novelty pet. It easily becomes attached to any means of transport or machinery at any developmental stage, is able to go into a state of aestivation in cooler conditions and so is readily transportable over distances. Once escaped it has managed to establish itself and reproduce prodigiously in tropical and some temperate locations. As a result, A. fulica has been classified as one of the world's top 100 invasive alien species by The World Conservation Union, IUCN (ISSG, 2003).
A. fulica is a polyphagous pest. Its preferred food is decayed vegetation and animal matter, lichens, algae and fungi. However, the potential of the snail as a pest only became apparent after having been introduced around the world into new environments (Rees, 1950). It has been recorded on a large number of plants including most ornamentals, and vegetables and leguminous cover crops may also suffer extensively. The bark of relatively large trees such as citrus, papaya, rubber and cacao is subject to attack. There are reports of A. fulica feeding on hundreds of species of plants (Raut and Ghose, 1984;Raut and Barker, 2002). Thakur (1998) found that vegetables of the genus Brassica were the most preferred food item from a range of various food plants tested. However, the preference for particular plants at a particular locality is dependent primarily on the composition of the plant communities, with respect to both the species present and the age of the plants of the different species (Raut and Barker, 2002). Crops in the Poaceae family (sugarcane, maize, rice) suffer little or no damage from A. fulica.
Given the polyphagous nature of A. fulica any host list is unlikely to be comprehensive. Those plant hosts included in this datasheet have been found in literature searches and Venette and Larson (2004).
A. craccivora is a relatively small aphid. Apterous viviparous females have a shiny black or dark brown body with a prominent cauda and brown to yellow legs. Immatures are slightly dusted with wax, adults without wax. Six-segmented antennae. Distal part of femur, siphunculi and cauda black. Apterae 1.4-2.2 mm.
Alate viviparous A. craccivora females have abdomens with dorsal cross bars. Alatae 1.4-2.1 mm (Blackman and Eastop, 2000).
On groundnut, very young rolled up leaves of seedlings should be examined for nymphs early in the season.
Groundnut plants take on a bushy appearance due to attack by A. craccivora and infection with rosette virus. Rosette may take two forms, chlorotic rosette (white patches with green veins on young leaves and short internodes) and green rosette (darker appearance with stunting of leaflets and branches).
A. craccivora is polyphagous, but with marked preference for Leguminosae, for example, Caragana, Lupinus, Medicago, Melilotus, Robinia, Trifolium and Vicia. It is found in small colonies on many other families, including Cruciferae.
S. nigrum is a very variable ephemeral, annual or sometimes biennial herb, 0.2–1.0 m tall, reproducing only by seed. It has a strong white taproot, with many lateral roots being produced in moist and fertile surface soils.
Stems vary from prostrate to ascending or erect, and from herbaceous in ephemeral plants to rather woody or even shrubby in those that survive long enough to be biennial. Stems are round or angular, smooth or sparsely hairy, and green to purplish.
Leaves are alternate, ovate and are carried on short stalks, 2–8 cm long, and vary between plants from smooth-edged to shallowly lobed. They are opaque, matt and dark green both above and below, and either smooth or finely hairy.
The small, white, star-shaped flowers are carried in umbels on slender stalks developing directly from the stems between the leaves. Each cluster usually carries from 5–10 flowers, which open sequentially over several days. The flowers are 5-8 mm across, and have prominent yellow centres.
Fruits are globular, dark green, matt berries 5–13 mm across, matt black when ripe, which contain many flattened, finely pitted, yellow to dark brown woody seeds approximately 1.5 mm long.
Seedlings of S. nigrum agg. all exhibit epigeal germination. The hypocotyl is commonly slender, about 1 cm long, green or purplish and distinctly hairy. The spreading cotyledons are slender, about 5 mm long, and taper towards the tips. The epicotyl is slender, smooth to finely hairy, and carries small, ovate, juvenile leaves that gradually assume the adult shape and size.
Although somewhat variable in size and coloration, adult specimens of H. halys range from 12 to 17 mm in length, and in humeral width of 7 to 10 mm. The common name brown marmorated stink bug is a reference to its generally brownish and marbled or mottled dorsal coloration, with dense punctation. Detailed redescriptions and diagnoses of adults are provided by Hoebeke and Carter (2003) and Wyniger and Kment (2010). Eggs are smooth and pale in colour, approximately 1.3 mm in diameter by 1.6 mm in length, and are laid in clusters of 20-30. The brightly coloured, black and reddish-orange first instars remain clustered about the egg mass after hatching and move away once moulting to second instars has occurred. There are five nymphal instars, which are described in Hoebeke and Carter (2003) with a key and illustrated with colour photos.
H. halys adults can be detected throughout the active growing season using blacklight traps and baited pheromone traps and nymphal populations can be detected with pheromone traps. However, each trap has limitations. Blacklight traps are attractive from early spring through September with reduced attractiveness as adults begin seeking overwintering sites. Baited pheromone trap effectiveness depends on the lure deployed. The use of methyl (2 E,4 E,6 Z)-decatrienoate only provides late season adult attractivess, whereas the use of (3 S,6 S,7 R,10 S)-10,11-epoxy-1-bisabolen-3-ol and (3 R,6 S,7 R,10 S)-10,11-epoxy-1-bisabolen-3-ol alone or in combination with methyl (2 E,4 E,6 Z)-decatrienoate provides season-long adult attractiveness.
In cropping systems, H. halys adults and nymphs can be detected through the use of timed visual counts, whole plant inspections, beat sheets counts and sweep netting. Timed visual counts are effective in field maize, nursery, nut, tree fruit and vegetable crops. Whole plant inspections are possible in various vegetables, field and sweetcorn by inspecting a specified number of plants per field or through the use of counts per linear foot of row. Beat sheet counts can be employed in nursery, nut and tree fruit;however, they are discouraged in nuts and tree fruit after thinning or June drop has occurred due to the potential removal of fruit. Sweep netting can be used in soyabeans but should be confined to field borders.
H. halys adults seek concealed, cool, tight and dry locations to overwinter. Because of this overwintering behaviour and need for specific microhabitats, many suitable sites can be generated by human-made materials and used by this insect as an overwintering sites such as inside cardboard boxes, other shipping containers and luggage, between wooden boards, within layers of folded tarps, and within machinery motors and vehicles. Thus, inspection for H. halys in shipments of goods from areas where it is present will require thorough visual inspections.
Adults and nymphs cause feeding damage. On tree fruits, feeding injury causes depressed or sunken areas that may become 'cat-faced' as the fruit develops. Late season injury causes corky spots on the fruit. Feeding may also cause fruiting structures to abort prematurely. Similar damage occurs in fruiting vegetables such as tomatoes and peppers, although frequently later in the season. Feeding can cause failure of seeds to develop in crops such as maize or soyabean. There is frequently a distinct edge effect in crop plots as H. halys has an aggregated dispersion and moves between crops or woodlots. In soyabeans, this can result in a 'stay green' effect where pods fail to senesce at the edges due to H. halys feeding injury.
Following the accidental introduction and initial discovery of H. halys in Allentown, Pennsylvania, USA, this species has been detected in 41 states and the District of Columbia in the USA. Isolated populations also exist in Switzerland, France, Italy and Canada. Recent detections also have been reported in Germany and Liechtenstein. BMSB has become a major nuisance pest in the mid-Atlantic region and Pacific Northwest, USA, due to its overwintering behaviour of entering human-made structures in large numbers. BMSB also feeds on numerous tree fruits, vegetables, field crops, ornamental plants, and native vegetation in its native and invaded ranges. In the mid-Atlantic region, serious crop losses have been reported for apples, peaches, sweetcorn, peppers, tomatoes and row crops such as field maize and soyabeans since 2010. Crop damage has also been detected in other states recently including Oregon, Ohio, New York, North Carolina and Tennessee.
H. halys has over 100 reported host plants. It is widely considered to be an arboreal species and can frequently be found among woodlots. Such host plants are important for development as well as supporting populations, particularly during the initial spread into a region. In Canada for example, established populations of H. halys have only been recorded in the Province of Ontario. Homeowner finds have previously been identified in the City of Hamilton (Fogain and Graff, 2011) as well as the Greater Toronto Area, the City of Windsor, Newboro and Cedar Springs (Ontario) (Fraser and Gariepy, unpublished data). However, preliminary surveys confirmed an established breeding population in Hamilton, Ontario, as of July 2012 (Fraser and Gariepy, unpublished data). At present, these populations are localized along the top of the Niagara escarpment in urban/natural habitats within Hamilton, and have not yet been recorded in agricultural crops. Reproductive hosts from which H. halys eggs, nymphs and adults have been collected on in Ontario include: ash, buckthorn, catalpa, choke cherry, crabapple, dogwood, high bush cranberry, honeysuckle, lilac, linden, Manitoba maple, mulberry, rose, tree of heaven, walnut and wild grape (Gariepy et al., unpublished data).
The list of host plants in Europe contains 51 species in 32 families, including many exotic and native plants. High densities of nymphs and adults were observed on Catalpa bignonioides, Sorbus aucuparia, Cornus sanguinea, Fraxinus excelsior and Parthenocissus quinquefolia (Haye et al., unpublished data).
Multiple host plants seem to be important for development and survival of H. halys. This species can complete its development entirely on paulownia (Paulownia tomentosa), tree of heaven (Ailanthus altissima), English holly and peach. More details on host plants and host plant utilization can be found at http://www.stopbmsb.org/where-is-bmsb/host-plants/ as well as http://www.halyomorphahalys.com, Panizzi (1997), Nielsen and Hamilton (2009b) and Lee et al. (2013a).
In Asia, H. halys is an occasional outbreak pest of tree fruit (Funayama, 2002). Damage to apples and pears in the USA was first detected in Allentown, Pennsylvania, and Pittstown, New Jersey (Nielsen and Hamilton, 2009a). In orchards where H. halys is established in the USA, it quickly becomes the predominant stink bug species and, unlike native stink bugs, is a season-long pest of tree fruit (Nielsen and Hamilton, 2009a;Leskey et al., 2012a). In particular, peaches, nectarines, apples and Asian pears are heavily attacked. Feeding injury causes depressed or sunken areas that may become cat-faced as fruit develops. Late season injury causes corky spots on the fruit. Feeding may also cause fruiting structures to abort prematurely. Similar damage occurs in fruiting vegetables such as tomatoes and peppers, although frequently later in the season. Feeding can cause failure of seeds to develop in crops such as maize or soyabean. There is frequently a distinct edge effect in crop plots as H. halys an aggregated dispersion and moves between crops or woodlots. In soyabeans, this can result in a 'stay green' effect where pods fail to senesce at the edges due to H. halys feeding injury.
The morphology of P. distichum has been described in detail by Chase (1929). It is a widely creeping perennial with slender rhizomes, extensively stoloniferous, often forming loose mats. The stolons are usually slender, subcompressed, sometimes as much as one metre long. On average, the sheaths are less loose than in Paspalum vaginatum, the blades are usually well developed;the branches are erect or ascending, most of them finally flowering, 6-50 cm tall, often sparingly branching. The culms are subcompressed, the nodes dark, often with a few ascending hairs;the sheaths are loose, keeled, and commonly pilose on the margins toward the summit. The ligule is membranaceous, about 0.5 mm long;the blades are flat, ascending, 3-12 cm long, and 2-6 mm wide at the rounded, ciliate base, tapering to an acuminate, sometimes involute apex;they are dull green, relatively soft in texture, and occasionally minutely pubescent on the upper surface. The peduncles are commonly short, often included;there are usually two racemes, rarely as many as four, from erect to reflexed, commonly incurved, 1.5-7 cm long, rarely longer. The rachis is slightly pedunculate in one, sometimes both racemes, usually with a few white hairs in the axil, 1-1.5 mm, rarely 2 mm wide, triangular, and minutely scabrous on the margin. The spikelets are solitary (rarely in pairs in the middle of the raceme), imbricate, 2.5-3 mm wide (size variation is sometimes found in the same plant), elliptic, abruptly acute, and pale green. The first glume is frequently developed;the second glume and sterile lemma are equal, with three to five veins, the midrib is relatively prominent. The glume is minutely appressed-pubescent, sometimes obscurely so. The fruit is 2.5-2.8 mm long, about 1.2 mm wide, and elliptic. Pollen morphology has been described by Ma GuoHua et al. (2001).
P. distichum is a fast-growing rhizomatous grass of wet areas. It has become a major weed of rice and many other crops, as well as occurring in uncropped wetlands in both its native and introduced regions. Its introduction to Europe, Asia and the Pacific is not well documented but apparently occurred many years ago. New records are reported in e.g. Indonesia, Spain and Croatia, suggesting that it continues to spread in countries to which it has been introduced.
Barbehenn et al. (1973) described R. exulans as the smallest of the 'typical' rats in the Philippines. Its average adult mass is 63 ± 2 g (mean ± SE) on Pacific islands and ranges from 39-120 g (Shiels and Pitt, 2014). Maximum head-body length is 180 mm;ears are 15.5-20.5 mm, and the hind foot averages 27 mm (range: 22-31 mm) (Atkinson and Towns, 2005). Plantar pads are well developed and lamellate. R. exulans often has dark-coloured upper sides of hind feet which is unlike R. rattus, R. norvegicus, and Mus musculus, which all have uniformly colouring over whole feet (Atkinson and Towns, 2005).
In ricefields, the presence of rats is indicated by cut tillers, scattered grains and leaves on the ground, foot prints and runways. In coconut groves, fallen nuts with holes are seen. In fruits and root crops, gnawed holes made by the rats’ sharp incisors are the common signs of damage. It is difficult to differentiate rodent species merely by the damage they cause. Faeces are not reliable indicators of species because of their sizes overlap with other rodent species (Atkinson and Towns, 2005;Shiels et al., 2014). R. exulans faeces generally range from 6.4-9.0 mm in length (Atkinson and Towns, 2005).
R. exulans often has dark-coloured upper sides of hind feet which is unlike R. rattus, R. norvegicus, and Mus musculus, which all have uniformly colouring over whole feet (Atkinson and Towns, 2005).
If more than one rodent species is suspected to be in the habitat or area, traps (snap traps and live traps) can be used to catch rats for proper identification. In the Philippines, the trapping period may be extended (more than three nights) to catch the dominant species (R. rattus mindanensis, R. argentiventer or R. norvegicus) during the first nights of trapping, before catching R. exulans. A similar pattern of R. rattus dominance during the first trap nights, and R. exulans only captured on nights after the first two nights, has been also found in Hawaii (Shiels, 2010).
For regular monitoring of R. exulans populations, use of tracking tiles (made of vinyl or other material) are common, where mimeographing ink is painted on half of the area of each tile and laid along the path of the rats (Sanchez and Benigno, 1985) or otherwise in the habitat of interest (Shiels, 2010).
The diet of R. exulans in agricultural areas can include rice, coconuts, maize, palms, sweet potatoes, white potatoes, cassava, sugarcane and insects (Kami, 1966;Wood, 1994). Animals can comprise a significant portion of the Pacific rat diet;arthropods are generally the most common animals consumed, yet less often seabirds, forest birds, land snails and lizards can also be consumed when available (Atkinson and Towns, 2005;Shiels and Pitt, 2014). Plant material generally dominates R. exulans diet in forests and agricultural settings (Stecker and Jackson, 1962;Williams, 1973;Shiels et al., 2013;Shiels and Pitt, 2014). In the Tokelau Islands, northeast of New Zealand, 87.6% of R. exulans diet was coconuts found on the ground (Mosby and Wodzicki, 1973).
Strecker and Jackson (1962) reported that field rats on the Pacific island of Pohnpei, including R. exulans, fed on cereals, groundnuts, sugarcane, candy, cheese, fish, meat, ripening bananas, tapioca, tomatoes, beans, pineapples, pawpaws, soursop (Annona muricata), cocoa, passion fruits, seeds on spikes of Bermuda grass (Cynodon dactylon), fruits of rainforest trees and snails.
Ultrastructural aspects of AY group phytoplasmas in sieve tube elements of diseased plants have been studied by several researchers using transmission and scanning electron microscope observations (Hirumi and Maramorosch, 1973;Haggis and Sinha, 1978;Marcone et al., 1995;Marcone and Ragozzino, 1996;Fránová and Šimková, 2009;Fránová et al., 2009). The phytoplasma bodies varied in size and shape. They showed a very high polymorphism, appearing in round, ovoid, encurved and elongated forms. Octopus-like structures, as well as budding, dimpled- and dumbbell-shaped forms were also observed. The size of spherical forms ranged from 100 to 800 nm and filamentous bodies were up to 2600 nm in length. However, the morphological variations observed most probably represented various developmental stages of phytoplasmas and they cannot be considered as distinctive characteristics.
For reliable diagnosis, the identity of phytoplasmas occurring in plants characterized by the symptoms described (see Symptoms), should be determined by molecular techniques.
AY group phytoplasmas affect plants by causing extensive abnormalities in plant growth and development, suggestive of profound disturbance in plant hormone balance. Symptoms typical on herbaceous plant hosts include yellowing of the leaves, stunting, proliferation of auxiliary shoots resulting in a witches'-broom appearance, bunchy appearance of growth at the ends of stems, virescence of flowers and sterility, phyllody, shortening of internodes, elongation and etiolation of internodes, small and deformed leaves. Yellowing, decline, sparse foliage and dieback are predominant in woody plant hosts. However, it is well-known that distantly related phytoplasmas can cause identical symptoms in a given host plant, whereas closely related phytoplasmas can cause distinctly different symptoms. Lee et al. (1992) determined that different symptoms could be induced in Catharanthus roseus (periwinkle) by closely related strains of the AY phytoplasma group.
AY group phytoplasmas appear to have a wide host range. The vast majority of strains in the AY group infect herbaceous dicotyledonous plant hosts. However, a number of strains that belong to subgroups 16SrI-A, 16SrI-B and 16SrI-C are capable of infecting monocotyledonous plants (e.g., maize, onion, gladiolus, oat, wheat and grass). Some strains in subgroups 16SrI-A, 16SrI-B, 16SrI-D, 16SrI-E, 16SrI-F and 16SrI-Q can induce disease in woody plants (e.g., grey dogwood, sandalwood, blueberry, mulberry, peach, cherry, olive, grapevine and paulownia). For many of the plant hosts which have previously been reported to be affected by AY diseases on the basis of symptomatology and/or microscopic examinations (see McCoy et al., 1989), the identity of the infecting phytoplasmas has never been determined with molecular techniques, or proved to be different from that of other established AY phytoplasma strains (Schneider et al., 1997;Marcone et al., 2000).
The live adult female is 2.9-5.0 mm long and 2.4-4.0 mm wide, with a pale yellow oval body covered in white wax or sulfur-yellow flocculent wax tinged with white. In the slide-mounted adult female, the antennae each have 9-11 segments and there are three pairs of abdominal spiracles towards the apex of the abdomen. The center of the abdominal venter becomes invaginated to form a marsupium into which the vulva opens, and there is a marsupial band of simple multilocular pores along the lip of the marsupium, which becomes sclerotized with age.
Foliage and stems should be inspected for lumps of white or yellow wax secreted by scale insects, symptoms of pest attack, attendent ants, sticky honeydew and sooty mould growth on leaves. A user-friendly, online tool has been produced for use at US ports-of-entry to help with the identification of potentially invasive scale insect species (Miller et al., 2014a,b).
Most damage to plants is caused by the early immature stages of I. samarai, which feed on the leaf undersides, settling in rows along the midrib and veins, and on smaller twigs. The older nymphs feed on larger twigs, and as adults they settle on larger branches and the trunk. Damage to plants results from phloem sap depletion during feeding, leading to shoots drying up and dying. Trees that are badly attacked suffer partial defoliation and a general loss of vigour. The insects dischargesugary honeydew, which can be copious in large colonies and may foul plant surfaces. Besides direct damage by feeding, indirect damage can result from the development of black sooty mould on the honeydew on leaf surfaces, blocking light and air from the plant, leading to a reduction in photosynthesis (Beardsley, 1955).
The scale insect Icerya samaraia (formerly Steatococcus samaraius) occurs in the Australasian, Oriental and Oceanic zoogeographic regions. It has a wide host range which includes mostly woody plant species in 40 genera belonging to 25 families. It is a minor pest of citrus, banana, coconut, guava, papaya, cocoa, pigeon pea and other plants, including forest and ornamental trees. Populations of I. samaraia are apparently being kept under control on the Palau Islands in the western Pacific Ocean by natural enemies, particularly by the introduced coccinellid Rodolia pumila. I. samaraia can be transported on infested plant materials because of its small size and habit of feeding in concealed areas, making it a potential threat as an invasive species.
I. samaraia has been reported on mostly woody plant species in 40 genera belonging to 25 families from the Australasian and Oriental zoogeographic regions (Miller et al., 2014a).
F. alnus is a deciduous shrub or small tree usually 4-5 m in height (Tutin et al., 1968), but may grow to 7 m (Gleason, 1963). It develops an erect, slender habit with branches somewhat irregular in alternate pairs, ascending at an acute angle to the main stem (Godwin, 1943). Young twigs are green but turn grey-brown with age and develop red-brown to dark violet tips. Lenticels may be evident as white dots and stripes. Lemon-yellow inner-bark tissues are exposed when the outer-bark is damaged and the young wood is dark brown. Old bark is smooth, except in very old specimens, and readily peels off dead wood. Spines are absent from F. alnus. Leaves are petiolate, obovate in shape, 2-7 cm in length and usually little more than half as wide. They are cuspidate to acuminate in shape, typically ending with a short pointed tip. Leaf margins are entire but wavy, although in seedlings leaves may be serrated. The lower surface of young leaves is pubescent, being covered with dense brownish hairs which are later shed so that older leaves are glabrous and shiny green in colour. Sun leaves are relatively broader and more shiny than shade leaves. The leaves turn yellow, then red in the autumn. Lateral veins are conspicuous on the upper surface of the leaves with 6-12 (commonly 7) pairs running more or less parallel to each other.
F. alnus develops sessile umbels in the leaf axils on young wood with 2-8 flowers borne on stout, unequal, glabrous pedicels 3-10 mm long;occasionally single flowers develop. Individual flowers are greenish-white, about 3 mm in diameter and bisexual. The flowers are 5-merous with broadly obovate petals 1-1.4 mm long and cleft at the tip (Gleason, 1963). Fruits are 6-10 mm in diameter, and change from green to red, then to violet-black on ripening;flowering and fruit development are rather asynchronous, hence all stages of ripening may be present. Each drupe usually contains 2, but occasionally 3, pyrenes or stones which are broadly obovoid in shape, about 5 mm long and 2 mm thick;they have a faint ridge running down the inner face and a deep furrow at the base. Young and Young (1992) report 52 seeds/g for F. alnus. Germination is hypogeal (Godwin, 1943).
F. alnus was introduced to North America from Europe more than 100 years ago. Once established it maintains itself due to prolific seed production, vigorous growth over an extended growing season and its ability to regenerate following burning and cutting. These characteristics make it difficult to eradicate. Repeated cutting and application of herbicides required to eliminate F. alnus is laborious and expensive. Consequently, most restoration work has been conducted in natural ecosystems of special interest. Its adverse effect on native species arises because F. alnus shades out understorey plants. Its aggressive character, especially in wetlands, is widely noted (Catling and Porebski, 1994).
F. alnus is a problem species in native communities because it establishes in dense stands which shade out other understorey species. Possessky et al. (2000) reported a reduction in composition and abundance of the herbaceous cover in riparian habitats in the northern Allegheny Plateau (of Pennsylvania, New York and Ohio, USA) following invasion by F. alnus. Similarly, Reinartz (1997) described how an undisturbed bog community in Wisconsin was invaded by F. alnus in 1955 with a dense tall shrub canopy dominating the site within 12 years. The species is listed as an invasive weed in Tennessee and Wisconsin, USA (Southeast Exotic Pest Plant Council, 1996;Hoffman and Kearns, 1997). F. alnus was recently rated as one of the six principal invasive aliens of wetlands in Canada, and one of four principal invasive aliens in Canadian uplands. In a national survey it was rated second to purple loosestrife (Lythrum salicaria) with respect to the extent to which it is spreading in natural habitats and its severity of impact in Canada (White et al., 1993).
F. alnus is associated with crown rust (Puccinia coronata) which infects several cool season turfgrasses, native grasses and cereals. The uredia, telia and basidiospores are produced on the graminoid hosts, the aecia and pycnia are produced on F. alnus (and Rhamnus cathartica;Partridge, 1998). Alfalfa mosaic virus, which infects a wide variety of plants, including crops, and is vectored by aphids, has also been isolated from young leaves and root cuttings of F. alnus in Italy (Marani and Giunchedi, 2002).
CBSVs have slightly flexuous particles with a modal length of ca 650 nm. Particles contain single-stranded genomic RNA of approximately 9008-9070 nt which is encapsidated in a coat protein of ca 43 kDa for UCBSV and ca 45 kDa for CBSV (Winter et al., 2010). The genome structure of the cassava brown streak viruses is unique because of a MAf/Ham1-like sequence inserted upstream the coat protein gene and a P1 gene to which gene silencing suppression function was assigned.
The name brown streak was given to the disease from the brown lesions which sometimes appear on young green stems. These were the first symptoms of the disease to be recognised, however stem lesions are not the most characteristic symptom of infection and occur only infrequently.;Unlike symptoms induced by the majority of plant viruses, those of CBSD in cassava normally affect mature or nearly mature leaves but not expanding, immature leaves. They consist of a characteristic yellow or necrotic vein banding which may enlarge and coalesce to form comparatively large, yellow patches. Tuberous root symptoms may also be present: these consist of dark-brown necrotic areas within the tuber and reduction in root size, lesions in roots can result in post-harvest spoilage of the crop. Leaf and/or stem symptoms can occur without the development of tuber symptoms, thus, of plants with above-ground symptoms surveyed in southern Tanzania, 21% failed to develop root necrosis (Hillocks et al., 1996).;The symptoms of the disease vary greatly with variety and environmental conditions, making diagnosis difficult, particularly when plants are infected both with CBSD and cassava mosaic disease.
C. glycines produces monophialidic, ampulliform, conidiogenous cells formed from the inner cells of the pycnidial wall (Hartman and Sinclair, 1988). Pycnidiospores are ellipsoidal, one-celled, and 4-8 µm long by 1-3 µm wide. Sclerotia range in size from 96 to 357 µm in diameter, and are mostly spherical, dark brown to black, and covered with setae, 5 to 36 µm long. It is interesting to note that when the name changed from Dactuliochaeta glycines to Phoma glycinicola (de Gruyter and Boerema, 2002) and then to C. glycines (de Gruyter et al., 2013), there was no mention of the importance of the sclerotia produced by the fungus. It appears that species of Phoma and Coniothyrium do not produce similar sclerotia to C. glycines, which makes this fungus unique in its biology. The uniqueness of the sclerotia may provide a characteristic that can be used for field diagnosis as they can be seen clearly with the aid of a hand lens.
There are limited or no exports of soyabean from countries in sub-Saharan Africa to countries outside of Africa, and there have been no documented cases of movement of the pathogen from countries with this disease. Any shipment of soyabean seeds from infected countries would need to enter the USA through a seed permit process managed by USDA APHIS. Similar permitting processes are presumably in place in other countries, which would be the first step in excluding the pathogen from establishment in countries without the disease.
C. glycines produces similar symptoms on soyabean and Neonotonia wightii. Initial symptoms can occur at the seedlings stage on unifoliolate leaves. Early lesion development is often associated with primary veins (see Pictures). Under conditions conducive for disease development, symptoms appear over time from the lower to the upper trifoliolate leaves as dark red blotches on the upper surfaces and similar reddish-brown blotches with dark borders on the lower surface s. The fungus also causes lesions on petioles, stems and pods (see Pictures).
Red leaf blotch affects soyabean in central and southern Africa. The disease and the causal fungus (Coniothyrium glycines) were first reported in Ethiopia in 1957. C. glycines is native to Africa, living on the native legume, Neonotonia wightii, and perhaps other native or non-native legumes. The jump of the pathogen to soyabean occurred as early as 1957 and reports of the occurrence of red leaf blotch have increased along with soyabean production in Africa. The disease is currently a serious threat to soyabean production in sub-Saharan African countries with losses of up to 70% reported. C. glycines is considered a threat to soyabean-producing countries such as Brazil and the USA. The pathogen is not known to be disseminated by seed or wind. Infection is thought to occur via rainsplash of soilborne inoculum onto the leaves of soyabean plants. Symptoms include characteristic dark red spots on the upper leaf surface and reddish-brown lesions with dark borders on the lower surface. Premature leaf drop may occur in heavy disease conditions, releasing sclerotia back into the soil. The disease is favoured by wet, humid conditions.
Soyabean is the only known crop host under field conditions. The only other host found to be naturally infected is Neonotonia wightii. The experimental host range through inoculation includes the crops cowpea, lima bean, pigeon pea and winter vetch, and non-crops Glycine argyrea, G. canescens, G. clandestina, G. cyrtoloba, G. falcata, G. latrobeana, G. soja [ G. max subsp. soja ], G. tabacina, G. tomentella, N. wightii and Pueraria lobata [ Pueraria montana var. lobata ] (Hartman and Sinclair, 1992).
D. sissoo is a medium to large, deciduous, long-lived tree with a spreading crown and thick branches. It attains a height of up to 30 m and a girth of 2.4 m;the bole is often crooked. In Rawalpindi district, Pakistan, it also occurs in the form of a straggling bush at an altitude of 1500 m, clinging to crevices in the sides of sandstone cliffs (Troup, 1921). The bark is thick, rough and grey, and has shallow, broad, longitudinal fissures exfoliating in irregular woody strips and scales (Luna, 1996). D. sissoo develops a long taproot from an early age and has numerous lateral ramifying roots (Hocking, 1993). The leaves are compound, imparipinnate and alternate, with rachis 3.5-8 cm long, swollen at the base. There are 3-5 leaflets, each 3.5-9 x 3-7 cm;leaflets alternate, broadly ovate, conspicuously and abruptly cuspidate at the apex, rounded at the base, entire, coriaceous, pubescent when young and glabrous when mature. The terminal leaflet is larger than the others, and there are 8-12 pairs of veins in the leaflets (Parker, 1956;Luna, 1996). The inflorescence of D. sissoo is an axillary panicle 3.5-7.5 cm long, with small flowers, 7-9 mm long, white to yellowish-white with a pervasive fragrance, sessile, papilionaceous and hermaphrodite. The standard petal is narrow at the base and forms a low claw;wing and keel petals are oblong. Pods are 4.5-10 x 0.7-1.5 cm, linear-oblong, indehiscent, stipitate, glabrous, apex acute, reticulate against the seeds, and usually 1-4 seeded. Seeds are kidney-shaped, variable in size (8-10 x 4-5.5 mm), pale brown, brown to brownish-black, reniform, compressed, with papery testa (Parker, 1956;Singh, 1989;Luna, 1996).
Pneumostome located on the right-hand side of the mantle and near the front margin;keel absent;mantle granular. Foot fringe broad, heavily lineolated, similar in colour to that of the back. Juveniles have dark lateral bands with paler ‘shadow’ bands on the sides above these – compare juvenile Arion rufus and juvenile and adult Arion subfuscus. Sides below the bands are pale. Colour is variable - yellowish, greyish, chocolate, reddish, brownish (never greenish). The adults are normally unbanded, colour of the upper surface a uniform yellowish-brown, brown, reddish-brown or dark-brown, rarely black. Eggs are white, slightly transparent, soft-shelled, ca 2 mm in diameter.
The occurrence of A. vulgaris in transported plant materials may involve the adults, juveniles or eggs.
The adults and juveniles are active after dark and may be detected in the evening or early morning, or by inspecting plant materials stored under cover. Like Deroceras reticulatum, all stages hide in leaf whorls, under debris, stones and wood and occasionally in the soil around root systems.
The eggs are deposited on the soil, under dead leaves or other surface debris and are not buried in the soil.
Traps containing molluscicides (metaldehyde, carbamate, iron pyrophosphate hydrate) may be used to collect material, but hand collecting is often just as efficient and avoids the risk of contaminating produce.
Copious deposits of slime and slime trails leading from damaged site indicate activity.
Damage only within 1-5 m from the field edge, next to an area with dense, undisturbed vegetation, for example, grassland, fallow, scrub and garden.
Surface damage to large plants or plant parts specifically indicates the presence of this species. Complete removal of plants may occur.
No damage occurs below ground with this species.
The invasiveness of A. vulgaris is related to several factors. Its ability and readiness to colonize humanly-disturbed environments is of major importance. Proschwitz (1997) observed that 99% of Swedish records were from synanthropic habitats and only 1% from natural woodlands. With a proximity to humans, comes the possibility of passive dispersal through trade, particularly in living plants. The garden centre trade and horticulture are particularly implicated (Weidema, 2006). In Poland, there is evidence from studies of molecular diversity that A. vulgaris has originated from repeated, separate introductions from other parts of Europe (Soroka et al., 2007).
A. vulgaris is a serious pest of diverse vegetable crops (especially Brassicaceae, lettuce, cucurbits), vegetable seedlings, arable crops (Triticaceae), ornamental plants, low-growing fruits (strawberries) and herbs within gardens in Central Europe, regularly causing severe losses. In the early stages of arable crop development (after seedling emergence or after planting), the plants are seriously defoliated or completely destroyed. The leaves, flowers or fruit may be damaged with feeding holes, and the potential harvest devalued. In Austria, serious damage to arable agriculture has been reported (Reischütz, 1984). In Poland, A. vulgaris was found to feed on a wide range of plants, including arable crops and commonly occurring weeds. Slug damage was found on 103 plant species (including wild species) and preferred crops including Brassica napus (Kozlowski and Kaluski, 2004;Kozlowski, 2005).
Ezzat (1956) and Green (1922) described I. insignis (as Orthezia insignis) in detail. Body of adult female is about 1.5 mm long and 1.3 mm wide (excluding the ovisac), brownish olive green;dorsum mostly bare of wax except for two narrow logitudinal rows of 12 small white wax processes, these rows situated on either side of the mid-line;the dorsal wax processes fairly short, the longest and most curled occurring towards the posterior end. Venter with white waxy areas around mouthparts and limb bases, and the white ovisac of sculpted wax arising from just posterior of the hind leg coxae and from a submarginal belt around the abdomen. Ovisac 1.5 - 3.5 mm long, of brittle wax plates, nearly parallel-sided, curving slightly upwards posteriorly, ending in a dorsal opening. Unlike most Coccoidea, I. insignis carries the ovisac attached to the body, rather than attaching it to the substrate. Antennae are 8-segmented, brownish, about 0.9 mm long, terminal segment longest. Eyes each situated on a conical projection just posterior to each antenna base.
Immature females lack any development of the ovisac but otherwise resemble smaller versions of the adult;first instar with body 0.3 mm long, antennae each 6-segmented, lacking ventral waxy areas and without bare area between dorsal rows of wax plates;second instar similar but larger;third instar larger again, with 7-segmented antennae and ventral waxy areas present.
Males are seldom produced (Green (1922) observed them produced at approximately four-year intervals in Sri Lanka). Adult male with body (excluding terminal wax filaments) 2.0 mm long;the single pair of wings appears greyish white with powdery wax;a pair of halteres present;antennae each 9-segmented, significantly longer than body, covered with short hairs;a pair of compound eyes present, each associated with a single ocellus;mouthparts absent;legs long and slender;abdomen terminates in a caudal tuft of white wax filaments arising from the antepenultimate segment.
Examine shrubs or trees closely for signs of sooty mould or sticky honeydew on leaves and stems, or ants running about. Look for I. insignis on twigs and stems (and sometimes on the underside of leaf midribs);the white ovisacs of the adult females are easily seen, especially when they walk about and the moving ovisacs catch the light. Good light conditions are essential for examination;in poor light, a powerful flashlight is helpful.
I. insignis extracts large quantities of sap, causing general host debilitation, but not death (Green, 1922). Build-up of sticky honeydew deposits occurs on nearby surfaces, which may attract attendant ants. Unsightly sooty moulds grow on the sugary deposits (Green, 1922), and badly fouled leaves may be dropped prematurely and the quality of fruits may be reduced. The older females are easy to see on young stems, especially when they walk about and the movement of the white ovisacs catches the light.
I. insignis is polyphagous, usually preferring woody hosts, occurring mainly on the shoots and twigs. Ben-Dov et al. (1998) list hosts from 34 plant families. It is most often found on trees and shrubs of the Verbenaceae (especially Lantana, Clerodendron and Duranta species), Solanaceae (especially Capsicum and Solanum), Acanthaceae, Compositae (especially Eupatorium and other ornamentals) and Rubiaceae (including Coffea). Green (1922) remarked that, while I. insignis damages numerous ornamental plants in Sri Lanka, it was not a pest on tea or coffee. Ezzat (1956) successfully reared I. insignis on sprouting potato tubers in Egypt, where he recorded the pest damaging a wide range of crops and utility plants such as sugarcane, Citrus, potatoes, tomatoes, chrysanthemums, shade trees such as Jacaranda, and windbreaks such as Casuarina.
Spermogonia sub-epidermal, mostly sub-globose, 80-110 x 85-120 µm. Aecia aecidioid, surrounded by a well-developed peridium;aeciospores formed in chains, mostly sub-globose to broadly ellipsoid, 17-25 x 15-22 µm, walls 1 µm thick, uniformly verrucose, no germ pore. Uredinia on abaxial leaf surface, cinnamon-brown;urediniospores broadly ellipsoid to obovoid-ellipsoid, 24-35 x 18-23 µm, walls 2-3 µm thick at sides, usually 4-8 µm thick apically, cinnamon-brown or chestnut-brown, uniformly echinulate, 3-4 obscure equatorial germ pores. Telia on abaxial surface, often confluent, early exposed, pulverulent, blackish-brown;teliospores broadly ellipsoid, obovoid-ellipsoid or oblong-ellipsoid, rounded at both ends, moderately constricted at septum, 28-52 x 14-24 µm, walls 1.5-2.5 µm thick at sides, 3-8 µm apically, chestnut-brown, pedicels hyaline, thick-walled, not collapsing, to 80–140 µm long, two-celled. See Ono and Azbukina (1997) for a more detailed description.
There is little published information on this plant pathogenic fungus, which has limited geographic distribution. As hosts exist in other regions of the world with similar environmental conditions, this species may pose a threat to native or agricultural plants if introduced.
PSTVd is a small, unencapsidated, covalently closed, circular RNA of circa 359 nucleotides. Variants consisting of 356-363 nucleotides have been described (Gross et al., 1978;Puchta et al., 1990;Lakshman and Tavantzis, 1993;Behjatnia et al., 1996;Verhoeven et al., 2010b). Electron micrographs reveal a rod-like conformation of 37+/-6 nm in length of the renatured state. In the denatured state, rod-like molecules as well as completely open circles are found (Riesner et al., 1979).
In crops like tomato and potato, symptoms may indicate the presence of a pospiviroid. After mechanical inoculation to potato cultivar Nicola all pospiviroids except Iresine viroid 1 (IrVd-1) evoked similar tuber symptoms although the intensity varied with viroid and with isolate. Pospiviroid infections in commercial tomato crops also incite symptoms independent of the viroid species (Verhoeven et al., 2004;EFSA Panel on Plant Health, 2011). However, mild strains may not evoke symptoms, and symptom development is affected by temperature and light (Diener, 1979;Harris and Browning, 1980). In addition, true seeds of potato (TPS) and tomato and plants for planting of ornamental species, the primary means of shipment, may not show symptoms. Therefore, diagnosis on the basis of symptoms alone is not acceptable for quarantine purposes. Laboratory tests are the most reliable method of detection (see Diagnosis). Kahn (1989) and Salazar (1989) give comprehensive reviews of plant protection measures and quarantine implications for viroids in general, and PSTVd in particular, respectively. Furthermore, an comprehensive list of management options for pospiviroids has been evaluated by the EFSA Panel on Plant Health (2011).
In potato, PSTVd can induce severe growth reduction;however, reduction may also be hardly visible. Vines of infected plants may be smaller, more upright, and produce smaller leaves than their healthy counterparts. Infected tubers may be small, elongated (from which the disease derives its name), misshapen and cracked. Their eyes may be more pronounced than normal and may be borne on knob-like protuberances that may even develop into small tubers. Symptom expression is influenced by the potato cultivar, strain of PSTVd, environmental conditions and method of inoculation (Pfannenstiel and Slack, 1980;Diener, 1987;Owens and Verhoeven, 2009).
The first symptoms of PSTVd infection in tomato are growth reduction and chlorosis in the top of the plant. Subsequently, this growth reduction may develop into stunting, and the chlorosis may become more severe, turning into reddening and/or purpling. In this stage, leaves may become brittle. Generally, this stunting is permanent;occasionally, however, plants may either die or partially recover. As stunting begins, flower and fruit initiation stop. Generally, the disease spreads along the rows (Mackie et al., 2002;Owens and Verhoeven, 2009).
Peppers display only very mild symptoms in response to PSTVd infection. The only visible symptom is a certain 'waviness' or distortion of the leaf margins near the top of infected plants (Lebas et al., 2005).
Infections of solanaceous ornamentals are usually symptomless (Verhoeven et al., 2008a, b, 2010b;Luigi et al., 2011).
Due to serious symptoms and large scale outbreaks, potato is considered the main host of PSTVd. However, many more hosts are known. The viroid also causes symptoms in tomato and pepper (Capsicum annuum) (Mackie et al., 2002;Lebas et al., 2005). In addition symptomless infections have been reported from avocado (Persea americana), Brugmansia spp., Chrysanthemum sp., Calibrachoa sp., Cestrum spp., Dahlia sp., Datura sp. Lycianthes rantonnei, Petunia sp., Physalis peruviana, Solanum pseudocapsicum, Streptosolen jamesonii, Solanum jasminoides, Solanum muricatum, sweet potato (Ipomoea batatas) and wild Solanum spp. (Salazar, 1989;Owens et al., 1992;Querci et al., 1995;Behjatnia et al., 1996;Di Serio, 2007;Verhoeven et al., 2008a, b, 2009, 2010b;Lemmetty et al., 2011;Luigi et al., 2011;Mertelik et al., 2010;Verhoeven, 2010;Tsushima et al., 2011). The experimental host range of PSTVd includes a wide range of Solanaceous species, as well as species from other families (Singh, 1973;Diener, 1979).
Ascomata hypophyllous, partially immersed, globose, reddish-brown, 200-350 µm diameter. Beak central, erect, 100-250 x 60-130 µm. Asci oblong, with tapering base and apical ring, 8-spored, (65-)78-80(-95) x 10-13 µm, free in ascoma at maturity. Periphyses clavate, 3-4 µ m thick. Ascospores biseriate, hyaline, 15-20 x 4-6 µ m, 1-septate, the lower cell much smaller, the upper cell usually biguttulate.
Leaves will show yellow to red leaf spots not restricted by leaf veins, often coalescing and turning brown. Affected leaves readily wither, curl up, and fall prematurely in the summer or remain on the tree through winter. Pycnidia, containing filiform conidia, form in the spots during the summer, and beaked perithecia develop in the leaves on the tree and on the ground in the autumn.
In Spain, pale-green spots appear on cherry [ Prunus spp.] leaves 4-8 wks after infection in the spring. The spots turn yellow to red, depending on the tree variety. Leaves fall prematurely. Reddish spots develop on the fruit and sometimes on the stem (Sanchez and Becedas, 2007). On apricot [ Prunus armeniaca ], spots are yellow to red, may become larger or merge, as they are not limited by leaf veins, and the affected areas or entire leaves become necrotic, turn brown and dry up (Smith et al., 1988). Spots are often irregular with chlorotic margins. Some leaves or fruits may fall prematurely, whereas others remain attached on the tree, providing the distinctive symptom of this disease (Lang, 2004;ERMES Agricoltura, 2009).
A. erythrostoma is a perithecial ascomycete known primarily from Europe, although it has also been reported from eastern Asia. The early spotting of leaves and fruits of Prunus species, particularly cherry and apricot [ Prunus armeniaca ], can result in significant defoliation and loss of yield in certain years when weather conditions are favourable for infection by airborne ascospores. Although there is no record of introduction of the fungus to new areas, which would most likely require transport of trees still bearing infected leaves and fruit, some countries do list it as a quarantine pathogen.
All Prunus spp. are considered possible hosts (see Hecht and Zinkernagel, 2006), but it is not clear that this would include the invasive species, Prunus serotina. In Korea, the host reported is Prunus serrulata var. spontanea (Cho and Shin, 2004).
Phytoplasmas (formerly mycoplasma-like organisms, MLOs) are pleomorphic, cell wall-less bacteria of the class Mollicutes that exist as obligate plant pathogens.
Phyllody and flower malformation appear usually in April/May and are easy to recognize in the field. Over the season, farmers can observe shoot proliferation or light green leaf development, but they normally do not associate such symptoms with a disease that cannot be controlled by using pesticides, and frequently treat the phytoplasma-infected trees with ineffective pesticides.
The most characteristic symptoms caused by AlmWB on almond trees are (i) shoot proliferation on the main trunk with the appearance of a witches’-broom, (ii) the perpendicular development of many auxiliary buds on the branches, with smaller and yellowish leaves, and (iii) the general decline of the tree with final dieback. A total loss of production happens 1-2 years after the initial appearance of the symptoms (Abou-Jawdah et al., 2002).
In the case of peach and nectarine trees, the first symptom observed is early flowering (15 to 20 days earlier than normal), followed by the earlier development of all the buds of the infected branches. In addition, phyllody at the flowering period and serrate, slim, light green leaves and witches’-brooms developing several months later from the trunk and the crown of the trees are observed (Abou-Jawdah et al., 2009). Even if the presence of witches’-broom is more common in almond trees than in peach/nectarine, the most important difference between peach/nectarine and almond symptoms is the development, in peach/nectarine trees, of phyllodies, never recorded on almond (Molino Lova et al., 2011).
Phytoplasmas are wall-less parasitic bacteria living exclusively in plant phloem as consequence of transmission by sap-sucking insect vectors (Lee et al., 2000);they have been associated with several hundred plant diseases. ‘ Candidatus Phytoplasma phoenicium’ (CaPphoe), subgroup 16SrIX-B, is the aetiological agent of almond witches’-broom (AlmWB), a severe disease affecting almond, peach and nectarine trees in Lebanon and Iran. The first epidemics of AlmWB occurred in almond trees in Lebanon in the early 1990s and in Iran in 1995. In Lebanon, the disease rapidly spread from coastal to high mountainous areas, killing almost 150,000 trees over a period of 15 years. CaPphoe was first added to the EPPO Alert List in 2001 and removed from the list in 2006. The more recent rapid spread of CaPphoe in peach and nectarine orchards and in other plant hosts, along with the identification of efficient insect vectors, increased the alarm about the risk it poses for stone fruit production in the Middle East and in all the countries of the Mediterranean basin. Thus it was re-inserted in the EPPO Alert List in 2015.
All almond (Prunus dulcis) varieties in the almond growing areas of Iran and Lebanon have been affected by AlmWB disease, but some varieties (e.g. Alwani and Awja in Lebanon and Sangi in Iran) are highly susceptible and develop severe witches’-brooms, leading to rapid death of the tree, while other varieties (e.g. Kachabi) are less affected (Verdin et al., 2003;Choueiri et al., 2001). Grafting experiments and molecular analyses indicate that AlmWB does not affect plum (P. domestica) or cherry (P. avium) trees (Abou-Jawdah et al., 2003). Nevertheless, its rapid spread on almond, peach (P. persica) and nectarine (P. persica var. nucipersica) orchards indicate a risk for epidemics in Lebanon and in the other countries of the Mediterranean area.
In Iran, ‘ Ca. P. phoenicium’ has not been identified in peach and nectarine but rather in other plant hosts, such as GF-677 (P. amygdalus × P. persica) and wild almond (Prunus scoparia) (Salehi et al., 2015), and more recently in apricots (P. armeniaca), in which it has been found to cause apricot yellows (Salehi et al., 2018).
Smilax aspera L. and Anthemis sp. are plant hosts preferred by the cixiid insect vectors Tachycixius viperinus (T. viperina) and T. cf. cypricus (T. cypricus) (Tedeschi et al., 2015). The leafhopper vector Asymmetrasca decedens was found feeding on Prunus scoparia (Salehi et al., 2015).
The description of B. japonicus given by the Flora of China Editorial Committee (2016) states:
Annual. Culms erect, 40–90 cm tall. Leaf sheaths pubescent;leaf blades 12–30 cm × 4–8 mm, both surfaces pubescent;ligule 1–2.5 mm. Panicle effuse, 20–30 × 5–10 cm, nodding;branches 2–8, 5–10 cm, slender, each bearing 1–4 spikelets. Spikelets lanceolate-oblong, 12–20 × ca. 5 mm, yellowish green, florets 7–11, closely overlapping;rachilla internodes shortly clavate, ca. 2 mm;glumes subequal, keel scabrid, margins membranous, lower glume 5–7 mm, 3–5-veined, upper glume 5–7.5 mm, 7–9-veined;lemmas elliptic, 8–10 × ca. 2 mm in side view, herbaceous, 9-veined, usually glabrous, margins membranous with conspicuous angle at maturity, scabrid, apex obtuse, minutely 2-toothed, awned from 1–2 mm below apex;awn 5–10 mm, longer on upper lemmas than lower lemmas, base slightly flattened, conspicuously recurved at maturity;palea shorter than lemma, ca. 1 mm wide, keels stiffly ciliate. Anthers ca. 1 mm. Caryopsis 7–8 mm. Fl. and fr. May–Jul. 2n = 14.
B. japonicus has relatively greater root development than B. tectorum (Hulbert 1955).
Wang et al. (1999) described a spectral-based sensor for detection and discrimination of wheat and weeds such as B. japonicus.
B;japonicus is an annual grass, originating in Eurasia and Northern Africa, which is introduced and invasive in rangelands in central and western North America, and a weed in wheat and other annual crops. It is an aggressive species that out-competes desirable vegetation for water and soil nutrients, thus reducing plant biodiversity. Invaded communities have reduced native vegetation cover and lower species richness than native rangelands. Seeds can remain viable in the soil for several years, making control difficult. B. japonicus is listed as a significant threat in Kentucky (Kentucky Exotic Pest Plant Council, 2013), is invasive in California (California Invasive Plant Council, 2016), and has an ‘Alert’ status in Tennessee (Tennessee Exotic Pest Plant Council, 2009). In Canada, it is listed as a noxious weed in Alberta and Saskatchewan.
Sori locular, 1-4 mm, in galls on stems, stolons and tubers. Sporiferous hyphae lining locules, producing spore balls to interior. Immature locules surrounded by brown corky tissue of potato [ Solanum tuberosum ].
Although malformed tubers are conspicuous (see Symptoms) and the spore sori are distinctive, there is no reliable inspection method to detect spores of T. solani on healthy tubers. A quarantine period is necessary to ensure that tubers are free of the fungus.
No symptoms are visible above ground. Infected tubers are misshapen or have warty swellings on the surface, and are hard. The whole or only part of the tuber may be infected. Numerous brown-black specks, interspersed with lighter-brown specks, can be seen in the flesh. The specks (spore sori) are 1 to 4 (or more) mm diameter and are filled with rusty brown spore balls. Completely infected tubers later become dry brown powdery masses of numerous spores. Galls resembling deformed tubers develop on the stems or stolons underground, often encircling them. Roots are not infected. On tomato [ Solanum lycopersicum ], galls develop particularly at the junction of the stem and roots.
For more information, see Barrus and Muller (1943), O'Brien and Thirumalachar (1972), Mordue (1988) and Torres (2001).
T. solani is a smut fungus attacking tubers and underground stems of Solanum, including potato [ Solanum tuberosum ] and tomato [ Solanum lycopersicum ], in the Andean region of South America. It is not restricted to the higher, cooler elevations, but has been a problem in coastal Peru (Bazan de Segura 1960;Zachmann and Baumann, 1975) and also occurs in Mexico. It may be transported in infected tubers and planting material and, very likely, on their surfaces if they become contaminated with the spores. The fungus survives in the soil and is difficult to eradicate;it can infect at least one common solanaceous weed. Losses of 80% or more have been reported in susceptible varieties. EPPO lists it as an A1 plant pest (OEPP/ EPPO, 1979).
The principal host is potato [ Solanum tuberosum ], but various other tuber-bearing species of Solanum are attacked, particularly Solanum tuberosum subsp. andigenum, as well as Solanum lycopersicum (tomato), and the solanaceous weed, Datura stramonium (Mordue, 1988).
Spermogonia, aecia and uredinia absent. Telia amphigenous, on indefinite spots, scattered or confluent, hemispherical, pulvinate, compact, erumpent, dark chestnut-brown. Teliospores oblong to clavate, rounded above, apex not thickened, rounded or attenuate below, 55-90 x 20-35 µm, up to 100 µm long, walls 2.0-2.5 µm thick, brown, upper cell with apical germ pore, lower cell with superior germ pore;pedicels hyaline, persistent, very long, up to 160 µm.
Both sides of the newest leaves of Buxus plants should be inspected for black pustules containing large, thick-walled, two-celled stalked spores. On plants without pustules, the newest leaves should be examined for spots accompanied by a thickening of the leaves.
Similarities to Other Species/Conditions
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No other rust fungi are reported on Buxus species. The asexual fungus Macrophoma candollei [ Dothiorella candollei ] also causes leaf spots on boxwood (Buxus sempervirens). Its small black pycnidia develop on the undersides of leaves, but the disease begins and is more severe on the oldest of the bush’s foliage, rather than on the newest leaves. The pycnidia produce tendrils, often called cirrhi, of single-celled spores (Batdorf, 1995).
Black telia develop on indefinite spots on thickened areas of the leaves (Grove, 1913). Smith et al. (1988) report hypertrophy and dieback of new growth caused by this rust.
P. buxi is an autoecious microcyclic rust, completing its life cycle with two spore forms on one host. It is native to parts of Europe and Asia. An introduction to the USA, is evidence that it can be invasive with respect to other temperate countries, particularly because its hosts in the genus Buxus are often propagated vegetatively and may carry latent infections. Boxwoods have long been popular as ornamentals, therefore the rust’s current absence from North America and temperate regions of the southern hemisphere is puzzling;in the earliest introductions of the host, the pathogen would probably have been ignored or overlooked. Conditions of boxwood cultivation may discourage the rust’s growth and survival.
The rust has been reported from Buxus sempervirens (boxwood) and Buxus microphylla (littleleaf boxwood), commonly grown ornamentals, as well as from the Asian species, Buxus sinica (Chinese boxwood), a cold-hardy species from Korea (Batdorf, 1995).
Adelges tsugae is a small (0.74mm), reddish-purple, aphid-like insect that covers itself with a white, waxy secretion. Both winged and wingless forms are present. Their mouthparts are thread-like and about 1.5mm long and used to suck sap. Eggs are brownish-orange but darken as the embryo matures. When the eggs hatch, reddish-brown crawlers move about actively in search of a suitable site to settle. The tiny crawlers can only be seen with a hand lens as they are barely visible to the naked eye. Once the crawlers settle, they insert their mouthparts into the plant at the base of the hemlock needles and remain in the same place for the duration of their life. Dormant first instar nymphs are black with a white fringe around the edge and down the centre of the back. The developing nymphs produce white, cottony, waxy tufts that cover their bodies. The white masses are 3mm or more in diameter. The presence of these masses on the twigs and bark of hemlock is a sure sign of A. tsugae.
The hemlock woolly adelgid (Adelges tsugae) is a small, aphid-like insect that has become a serious pest of eastern hemlock and Carolina hemlock. The most obvious sign of infestation is the presence of white, woolly egg masses on the underside of hemlock needles. Infested eastern North American hemlocks defoliate prematurely and will eventually die if left untreated. A. tsugae is a difficult insect to control as the white waxy secretion protects it from pesticides. It is dispersed to new habitats through the nursery trade and locally by wind, birds, mammals and humans. Hemlock trees provide important habitats for many wildlife species and A. tsugae has severe adverse ecological impacts which will become more severe as its distribution expands. Explanations for the rapid and invasive expansion of A. tsugae include a lack of natural enemies, a lack of resistance or tolerance to infestation by eastern hemlock and Carolina hemlock, and large reproductive output (Trotter and Shields, 2009).
Some of the adults produced during the spring generation are winged individuals that are unable to reproduce on hemlock, therefore they leave the hemlock tree in search of spruce, the alternate host. But because no suitable spruce host is available in North America, they soon die. Hemlocks growing in poor conditions (compacted soils, ledgy soils, poor drainage, drought prone, etc.) are much more likely to succumb within 3-5 years from invasion. Hemlocks growing under better growing conditions have been shown to withstand infestations longer.
The yellow or pale-orange, elongate-oval eggs, are ca 1.2 mm long. They are laid in groups of 12-25 on the underside of potato leaves. The females glue them to the leaf by one end using a special secretion. The long axis of the egg is almost perpendicular to the leaf. Eggs within a mass tend to form irregular rows and hatch simultaneously.
Body strongly convex dorsally, with large abdomen. Head, bearing 6 ocelli behind the antenna on each side and a pair of 5-dentate mandibles. Three thoracic segments, each bearing a pair of 3-segmented legs, plus claw. Abdomen 9-segmented. Colour changing with development, first instar cherry-red with shiny, black head and legs;later instars becoming progressively carrot-red, then pale orange in final instar.
Head, legs and posterior part of pronotum black to deep brown;two conspicuous rows of dark spots occur on the lateral aspects of the mesothoracic and abdominal segments 1 to 7, the uppermost surrounding the spiracles, and also segments 8 and 9 with dark dorsal plates. Setae when present are very small, some occur on the head, legs, pronotum, on the pigmented areas and ventrally. Spiracles small, annular with black peritremes and situated on the mesothorax and first 8 abdominal segments. Body length of full-grown larva about 15 mm.
A detailed generic diagnosis of Leptinotarsa larvae is provided by Cox (1982) and the first instar is described by Peterson (1951). The weights of the four larval instars are given by Balachowsky (1963).
Yellowish, bearing short setae on low, conical, brown tubercles. Head bearing several short setae, mandibles apically unidentate. Thorax with pronotum bearing about 100 setae;meso- and metathorax much more sparsely setose;apices of femora bearing about 3-5 setae and apical tarsal segment 1 seta. Abdominal segments 1-6 with lateral expansion dorsal to spiracle, dorsally bearing about 48 short setae, laterally about 9 setae on large papilla ventral to spiracle. Apical abdominal segment bearing a single, brown, median, sharply-pointed urogomphus or spine. Spiracles situated on mesothorax and abdominal segments 1-8;peritremes dark brown, but pale on abdominal segments 6-8. For further details, see Cox (1996).
Head, pronotum and venter yellow-orange with black markings, legs and scutellum orange-yellow, elytra yellow-orange with five longitudinal black stripes. Apical segment of maxillary palpi cylindrical, rounded apically, shorter than preceding segment. Elytra punctate-striate, epipleura glabrous. Mesosternum not raised above level of prosternum. Profemora normal, third tarsal segment entire, tarsal claws simple, divergent, not fused basally. Body length 8.5-11.5 mm.
The genus was revised by Jacques (1988). A key to the North American species is given by Wilcox (1972) and Jacques (1985).
Adults and larvae are easily seen because of their large size. L. decemlineata has a tendency to release its hold on plants that are shaken and this characteristic can be used to detect insects hidden among foliage. Visual sampling of potato fields was as efficient for estimating population density as the whole-plant bag-sampling method, and more efficient than sweep netting (Senanayake and Holliday, 1988). Soil sampling at harvest for buried beetles in diapause provides reliable results in area surveys (Glez, 1983). A sequential sampling plan has been reported for estimating populations of Colorado potato beetle egg masses and of adults and larvae (Hamilton et al., 1997a).
Colorado beetle principally attacks an introduced field crop grown as a monoculture, but not to an extent that has affected the area of the crop grown. It is not accordingly invasive in the usual environmental sense. It has no effects on the environment.
L. decemlineata attacks potatoes and various other cultivated crops including tomatoes and aubergines. It also attacks wild solanaceous plants, which occur widely and can act as a reservoir for infestation. The adults feed on the tubers of host plants in addition to the leaves, stems and growing points.
Descriptions of L. trifolii refer to fresh materials. Dry specimens may be distorted due to the manner in which they have been preserved. Also, the age of the specimen, when killed, will have some effect on its preservation characteristics.
For accurate identification, examination of the leaf mine and all stages of development are crucial.
L. trifolii eggs are 0.2-0.3 mm x 0.1-0.15 mm, off white and slightly translucent.
This is a legless maggot with no separate head capsule, transparent when newly hatched but colouring up to a yellow-orange in later instars and is up to 3 mm long. L. trifolii larvae and puparia have a pair of posterior spiracles terminating in three cone-like appendages. Spencer (1973) describes distinguishing features of the larvae. Petitt (1990) describes a method of identifying the different instars of the larvae of L. sativae, which can be adapted for use with the other Liriomyza species, including L. trifolii.
This is oval and slightly flattened ventrally, 1.3-2.3 x 0.5-0.75 mm with variable colour, pale yellow-orange, darkening to golden-brown. The puparium has posterior spiracles on a pronounced conical projection, each with three distinct bulbs, two of which are elongate. Pupariation occurs outside the leaf, in the soil beneath the plant.
Menken and Ulenberg (1986) describe a method of distinguishing L. trifolii from L. bryoniae, L. huidobrensis, and L. sativae using allozyme variation patterns as revealed by gel electrophoresis.
L. trifolii is very small: 1-1.3 mm body length, up to 1.7 mm in female with wings 1.3-1.7 mm. The mesonotum is grey-black with a yellow blotch at the hind-corners. The scutellum is bright yellow;the face, frons and third antennal segment are bright yellow. Male and female L. trifolii are generally similar in appearance.
L. trifolii are not very active fliers, and in crops showing active mining, the flies may be seen walking rapidly over the leaves with only short jerky flights to adjacent leaves.
The frons, which projects very slightly above the eye, is just less than 1.5 times the width of the eye (viewed from above). There are two equal ors and two ori (the lower one weaker). Orbital setulae are sparse and reclinate. The jowls are deep (almost 0.33 times the height of the eye at the rear);the cheeks form a distinct ring below the eye. The third antennal segment is small, round and noticeably pubescent, but not excessively so (vte and vti are both on a yellow ground).
Acrostical bristles occur irregularly in 3-4 rows at the front, reducing to two rows behind. There is a conspicuous yellow patch at each hind-corner. The pleura are yellow;the meso- and sterno-pleura have variable black markings.
Length 1.3 -1.7 mm, discal cell small. The last section is M(sub)3+4 from 3-4 times the length of the penultimate one.
The shape of the distiphallus is fairly distinctive but could be mis-identified for L. sativae. Identification using the male genitalia should only be undertaken by specialists.
The head (including the antenna and face) is bright yellow. The hind margin of the eye is largely yellow, vte and vti always on yellow ground.
The mesopleura is predominantly yellow, with a variable dark area, from a slim grey bar along the base to extensive darkening reaching higher up the front margin than the back margin. The sternopleura is largely filled by a black triangle, but always with bright yellow above.
The femora and coxa are bright yellow, with the tibia and tarsi darker;brownish-yellow on the fore-legs, brownish-black on the hind legs. The abdomen is largely black but the tergites are variably yellow, particularly at the sides. The squamae are yellowish, with a dark margin and fringe.
Although individual specimens may vary considerably in colour, the basic pattern is consistent.
L. trifolii are small black and yellow flies which may be detected flying closely around host plants or moving erratically and rapidly upon the leaf surfaces. Inspection of the leaf surface will reveal punctures of the epidermis and the obvious greenish-white mines with linear grains of frass along their length. For accurate identification, examination of the leaf mine and all stages of development are crucial.
L. trifolii larvae will be found feeding at the end of the mine, or the mine will end with a small convex slit in the epidermis where the larva has left the mine to pupariate on the ground. Sometimes the puparium may be found adhering to the leaf surface, although in most cases the fully-fed larva will have found its way to the ground beneath the plant to pupariate. This is especially true in hot, dry conditions where the larva/puparia would quickly desiccate if exposed on the leaf surface. Empty puparial cases are split at the anterior end, but the head capsule is not usually separated from the rest of the case.
Mined leaves should be collected into polythene bags and transferred to a press as soon as possible. Leaves containing larvae intended for breeding should be collected into individual polythene bags, which on return to the laboratory should be slightly over-pressurized by blowing into them before sealing the end. Blowing up the bag by mouth and sealing it adds valuable carbon dioxide to the moist air mix. Constant attention is required to ensure that puparia are transferred to individual tubes until the fly emerges. If the plant material begins rotting, good material with feeding larvae must be removed to more sanitary conditions.
When puparia are observed they can be very carefully removed to tubes containing a layer of fine sand, or a small strip of blotting paper or filter paper. This should be kept damp (never wet) until the adult emerges.
On emergence, the fly should be kept for at least 24 hours to harden up. Do not allow condensation to come into contact with the fly, or it will stick to the water film and be damaged.
Field collection of the adult L. trifolii is done by netting. The use of sticky traps, especially yellow ones, placed near host plants is a very effective method of collection and estimation of infestation.
If the puparial stage is collected from the soil, care must be taken not to damage the puparial skin or death will almost certainly follow. The pupae should be stored in glass tubes on a layer of clean sand or, better still, thick filter paper. The tube must have high humidity, but be free of condensation.
When the fly emerges, it must be allowed to harden for 24 hours before killing for identification purposes. Ensure that the tube has no condensation present.
Newly emerged adult L. trifolii are generally softer than specimens aged for several days and may crinkle as drying proceeds, especially the head. The ptilinal sac may still protrude from the suture between the frons and face obliterating some important characteristics. Adults should be dried slowly in the dark in a sealed receptacle over blotting paper. If preserving wet is preferred, the live specimen should be dropped into 20-40% alcohol, and transferred to 70-90% alcohol after 2 days.
L. trifolii feeding punctures appear as white speckles between 0.13 and 0.15 mm in diameter. Oviposition punctures are usually smaller (0.05 mm) and are more uniformly round.
L. trifolii leaf mines can vary in form with the host plant, but when adequate leaf area is available they are usually long, linear, narrow and not greatly widening towards the end. They are usually greenish white.
In very small leaves the limited area for feeding results in the formation of a secondary blotch at the end of the mine, before pupariation. In Kenya, Spencer (1985) notes the growth of many L. trifolii from mines which began with a conspicuous spiral. This is not a characteristic associated with L. trifolii on other continents.
The frass is distinctive in being deposited in black strips alternately at either side of the mine (like L. sativae), but becomes more granular towards the end of the mine (unlike L. sativae) (Spencer, 1973).
Fungal destruction of the leaf may also occur as a result of infection introduced by L. trifolii from other sources during breeding activity. Wilt may occur, especially in seedlings.
The host range of L. trifolii includes over 400 species of plants in 28 families including both ornamental crops (Bogran, 2006) and vegetables (Cheri, 2012). The main host families and species include: Apiaceae (A. graveolens);Asteraceae (Aster spp., Chrysanthemum spp., Gerbera spp., Dahlia spp., Ixeris stolonifera, Lactuca sativa, Lactuca spp., Zinnia spp.);Brassicaceae (Brassica spp.);Caryophyllaceae (Gypsophila spp.);Chenopodiaceae (Spinacia oleracea, Beta vulgaris);Cucurbitaceae (Cucumis spp., Cucurbita spp.);Fabaceae (Glycine max, Medicago sativa, Phaseolus vulgaris, Pisum sativum, Pisum spp., Trifolium spp., Vicia faba);Liliaceae (A. cepa, Allium sativum) and Solanaceae (Capsicum annuum, Capsicum frutescens, Petunia spp., Solanum lycopersicum, Solanum spp.) (EFSA, 2012).
It is now considered to be the most important pest of cowpea (Vigna uniguilata), towel gourd (Luffa cylindrica), cucumber (Cucumis sativus) and many other vegetable crops in southern China (Gao, 2014). In Europe, L. trifolii is a major pest of lettuce, beans, cucumber and celery, Capsicum sp., carnations, clover, Gerbera sp., Gypsophila sp., lucerne, Senecio hybridus, potatoes and tomatoes (EFSA, 2012). It is now a major pest of the Compositae worldwide, particularly chrysanthemums (including Dendranthenum, the commercial 'Mum') in North America, Colombia, and elsewhere. It also causes severe damage to different open field crops, such as chili peppers in Mexico.
L. invasa females usually prefer newly developed leaves, where they lay their eggs in the midribs, petioles and parenchyma tissue of twigs. Usually eggs are laid in a lined group at a distance of 0.3-0.5 mm of each other (Mendel et al., 2004;Shylesha, 2008). After hatching, the larva remains in a tissue cavity and its growth and gall development take place simultaneously. Gall development consists of five stages, described in Mendel et al. (2004):
- First stage: at the deposition site, a little spot of dead cells (epidermic and sub-epidermic), similar to a cork tissue, becomes evident, without any initial gall-shaped formation (Jacob and Ramesh, 2009;Kumar et al., 2015). A change in colour from green to pink or reddish usually occurs to the cells of midribs containing the eggs, and the spherical shape of the gall starts to be visible at the end of the stage, usually 1-2 weeks after deposition (Mendel et al., 2004;Jacob and Ramesh, 2009).
- Second stage: in the following days galls reach their maximum size and attain the typical green bump-shape (Jacob and Ramesh, 2009;Kavitha Kumari et al., 2010;Eyidozehi et al., 2014).
- Third stage: galls start to lose their green colour, turning into a glossy reddish colour (ICFR, 2011).
- Fourth stage: galls lose their glossiness, turning into dull pink/dark red (Kavitha Kumari et al., 2010).
- Fifth stage: corresponds to adult emergence, with exit holes visible on the galls surface. Gall colours turn to light brown on the leaf or red-brown on the stems.
Gall formation on leaf petioles, midribs and young twigs usually results in leaf shape deformation. Heavy infestations can firstly cause leaf deformation, due to curling of the midribs, premature aging and leaf fall (Nugnes et al., 2015), and eventually stunted growth of the tree (Mendel et al., 2004;Eyidozehi et al., 2014). Heavy infestation can seriously damage young plantations and nursery seedlings, although tree mortality has not been observed to date (EPPO, 2006).
Leptocybe invasa is believed to be native to Australia or to the native range of its host plants Eucalyptus - Australia, New Guinea, Indonesia and Philippines -, although it has only been detected in Australia in Queensland and New South Wales. During the last two decades, L. invasa has spread worldwide, invading all the continents where Eucalyptus has been imported to (Asia, Africa, Europe, South and North America). The invasive potential of L. invasa is very high. Its broad host range, polyvoltinism, overlapping generations, concealed life style (galls) and reproductive modalities allow the pest to quickly spread and exponentially grow from few individuals. L. invasa is considered thelytokous because sex ratio of the most widespread lineage is female biased, but a biparental lineage also exists.
The majority of Eucalyptus species have been confirmed to be susceptible to L. invasa (Jorge et al., 2016). Among these, E. camaldulensis (var. camaldulensis and obtusa), E. grandis, E. robusta and E. tereticornis showed remarkably high susceptibility to the blue gum chalcid (Mendel et al., 2004;Thu et al., 2009;Nyeko et al., 2010). Studies carried out on several clonal hybrids or clones of these species showed that the incidence of L. invasa infestation could affect them differently (Nyeko et al., 2010;ICFR, 2011). E. gomphocephala and E. occidentalis did not show susceptibility to L. invasa, while E. erythrocorys exhibited “cork tissue” symptoms some days after deposition, but no further gall formation was observed (Mendel et al., 2004).
To date, the only susceptible species not belonging to the Eucalyptus genus is Corymbia polycarpa (Thu et al., 2009), with other species of this genus (C. citriodora, C. maculata, C. torelliana) apparently being tolerant (Mendel et al., 2004).
The egg of L. botrana is of the so-called flat type, with the long axis horizontal and the micropile at one end. Elliptical, with a mean eccentricity of 0.65, the egg measures about 0.65-0.90 x 0.45-0.75 mm. Freshly laid eggs are pale cream, later becoming light grey and translucent with iridescent glints. The chorion is macroscopically smooth but presents a slight polygonal reticulation in the border and around the micropile. The time elapsed since egg laying may be estimated by observing the eggs: there are five phases of embryonic development - visible embryo, visible eyes, visible mandibles, brown head and black head (Feytaud, 1924). As typically occurs in the subfamily Olethreutinae, eggs are laid singly, and more rarely in small clusters of two or three.
There are usually five larval instars. Neonate larvae are about 0.95-1 mm long, with head and prothoracic shield deep brown, nearly black, and body light yellow. Mature larvae reach a length between 10 and 15 mm, with the head and prothoracic shield lighter than neonate larvae and the body colour varying from light green to light brown, depending principally on larval nourishment.
Older larvae are characterized by a typical dark border at the rear edge of the prothoracic shield (Varela et al., 2010) and by the black colour of the second antennal segment. The width of the head capsule is used to distinguish larval instars (Savopoulou-Sultani and Tzanakakis, 1990;Delbach et al., 2010) as well as mandible length (Pavan et al., 2010).
Inspection of Grapevine Reproductive Organs
Inspect inflorescences and look for eggs or larvae on flower buds or glomerules. Inspect grapes and look for eggs or larvae, or damaged berries. It is easier to look for larval damage rather than for eggs, because detection of eggs is very tedious and time-consuming, especially under field conditions. Egg detection is always preferable when an insecticidal control has to be programmed.
Corrugated Paper Bands
This technique has sometimes been employed to trap and quantify overwintering pupae. Bands are placed around grapevine trunks or primary branches, and diapausing larvae pupate inside. However, this method is only useful in the last generation, and its reliability is uncertain.
Their lack of specificity makes their use inadvisable when the adult trapping methods described below are available. EGVM flight activity mainly occurs at dusk (Lucchi et al., 2018c);this negatively affects the visibility of the light traps, impacting on their efficiency.
These traps were largely used in the past before sexual traps were developed, but may still be useful in particular situations. Trapping females with food-baited traps is a valuable tool to predict the onset of oviposition, an event used to properly time insecticide treatments (Thiéry et al., 2006). An earthen or glass pot is baited with a fermenting liquid (fruit juice, molasses, etc.) and the scents produced attract adults which are then drowned;the population may be estimated by counting. Practical problems include irregularity in trapping because fermentation strongly depends on seasonal temperature, trap maintenance (lure replenishment and foam elimination), and low selectivity. Terracotta pots baited with red wine have been used in Spain to assess the L. botrana mating ratio in mating disrupted vineyards (Bagnoli et al., 2011).
Pheromone traps are easier to use compared to feeding traps. They are a sensitive tool to monitor ﬂight of males exclusively, but can be useful to time an ovicidal treatment, and to properly schedule scouting activities in the vineyard. Sexual traps were first suggested by Götz (1939). Chaboussou and Carles (1962) designed traps baited with living L. botrana females, which became increasingly important for monitoring. To obtain a large number of females to bait traps, laboratory rearing methods were improved both on natural substrates (Maison and Pargade, 1967;Roehrich, 1967a;Touzeau and Vonderheyden, 1968), and on synthetic or semi-synthetic media (Moreau, 1965;Guennelon et al., 1970, 1975;Tzanakakis and Savopoulou, 1973). However, sexual trapping became more efficient when the major compound of the L. botrana sex pheromone, (7E, 9Z)-7, 9-dodecadienyl acetate, was described (Roelofs et al., 1973), identified from the female sex gland (Buser et al., 1974), and synthesized (Descoins et al., 1974). In traps, females were promptly replaced by dispensers impregnated with synthetic pheromone, which had essential practical advantages for monitoring. It has now been shown that the L. botrana sex pheromone is a blend of 15 compounds (Arn et al., 1988), but for economic reasons commercial traps incorporate only the major pheromone compound, which has a satisfactory trapping specificity for L. botrana. In Italy, males of few species of non target moths are sometimes captured in L. botrana pheromone traps (Ioriatti et al., 2004).
A major limitation of L. botrana sexual trapping (as often occurs in other insect pests) is the lack of a clear relationship between the number of males trapped and the damage done by their offspring, given the high number of other uncontrolled ecological factors involved. The correlation between these variables has been partially improved by diminishing the pheromone dose in traps (Roehrich et al., 1983, 1986). According to Roehrich and Schmid (1979), only a negative prediction can be made when male catches in traps are sporadic (or nil) can one expect minimal (or even no) damage to be caused by offspring on the crop;but if catches are moderate or high, the damage caused by offspring is unpredictable. Nowadays, the variable performance of the traps on the market, the influence of the trap placement and of the wind direction on the number of catches, make it still difficult to find a strict relationship between catches and infestation, especially when the catches are low.
Forecasting models and moth trapping alone do not provide sufﬁcient population density information and need to be supplemented with appropriate ﬁeld scouting of eggs and young larvae (Shahini et al. 2010).
Insecticides are applied according to action thresholds (AT) on the basis of the resulting infestation assessment (percentage of injured clusters, number of nests per inﬂorescence, number of eggs and larvae per cluster, number of injured berries per cluster). The action thresholds vary widely depending on the generation, susceptibility of the cultivar to subsequent infection by B. cinerea, and whether berries are being produced for table grape, raisins or wine production.
Predictive mathematical models have been developed and tested to forecast the life cycle of L. botrana, integrating both biological and climatic information. Temperature-based models, both linear (degree-days accumulated above a lower threshold) and non-linear (deterministic) have been generated in Switzerland (Schmid, 1978), France (Touzeau, 1981), Slovakia (Gabel and Mocko, 1984b, 1986) and Italy (Caffarelli and Vita, 1988;Baumgartner and Baronio, 1989;Cravedi and Mazzoni, 1990). Major problems affecting the correct inference of tortricid populations using modelling are summarized by Knight and Croft (1991) - it should be noted that prognosis is usually only qualitative. However, modelling can be a useful implement in L. botrana management programmes. Time of the ﬁrst appearance of adults and hatching of the ﬁrst eggs can be forecasted by predictive models based on temperature requirements of individual instars and critical conditions for oviposition (Moravie et al., 2006). Unfortunately, forecast models based on Degree Days are empirical and their robustness is strongly dependent on the environment in which they have been validated. Alternative forecasting techniques are currently under development, such as the evaluation of larval age distribution during the previous generation in order to predict the distribution of female emergence (Delbac et al., 2010).
The following description refers to grapevine, on which symptoms largely depend on the phenological stage of the reproductive organs.
On inflorescences (first generation), neonate larvae firstly penetrate single flower buds. Symptoms are not evident initially, because larvae remain protected by the top bud. Later, when larval size increases, each larva agglomerates several flower buds with silk threads forming glomerules (nests) visible to the naked eye, and the larvae continue feeding while protected inside. Larvae usually make one to three glomerules during their development which provide protection against adverse conditions, i.e., insulation, rain and natural enemies. Despite the hygienic behaviour of larvae, frass may remain adhering to the nests.
On grapes (summer generations), larvae feed externally and penetrate them, boring into the pulp and remaining protected by the berry peel. Larvae secure the pierced berries to surrounding ones by silk threads to avoid falling. Frass may also be visible. Each larva is capable of damaging between 2 and 10 berries, and up to 20-30 larvae per cluster may occur in heavily attacked vineyards (Thiery et al., 2018). If conditions are suitable for fungal or acid rot development, a large number of berries may be also affected by Botrytis cinerea, Aspergillus carbonarius and Aspergillus niger, which result in severe qualitative and quantitative damage (Delbac and Thiery, 2016). Damage is variety-dependent: generally it is more severe on grapevine varieties with dense grapes, because this increases both larval installation and rot development.
Larval damage on growing points, shoots or leaves is unusual (Lucchi et al., 2011).
Lobesia botrana should be regarded as a potentially serious pest on a worldwide scale for all the vine-growing areas that are presently unaffected.
The host plants listed for L. botrana have been compiled principally from Silvestri (1912), Voukassovitch (1924) and references therein;Ruíz-Castro (1943), Bovey (1966), Galet (1982), Stoeva (1982), Vasil'eva and Sekerskaya (1986), Moleas (1988), Savopoulou-Soultani et al. (1990), Gabel (1992) and Ioriatti et al. (2011).
Despite the wide host range recorded, grapevine is the major host crop in which damage is really important. With regard to wild hosts, Daphne gnidium is the major food plant (Lucchi and Santini, 2011). This species was thought to be the original wild host before the invasion of vineyards by L. botrana in the nineteenth century (Marchal, 1912), although this hypothesis has often been questioned (Bovey, 1966) and is still controversial.
Other hosts not selected naturally by females for egg laying have been tested satisfactorily under both laboratory and field conditions, constituting an adequate larval food;see, for example, Voukassovitch (1924) and references therein, including particularly studies by Dewitz, Wismann, Bannhiol and Lüstner;Bovey (1966) and Stavridis and Savopoulou-Soultani (1998).
However, some crops traditionally assumed in the older literature to be natural hosts of L. botrana, for example, Medicago sativa (lucerne) and Solanum tuberosum (potato), are not in fact naturally selected hosts.
Eggs are laid under frass caps on the external surface of the bracts of the pre-flowering capitulum. The four instars of larval development and pupation occur inside the capitulum. The adult is a typical ‘snout-beetle’, 6 (3-7) mm long. It is dark in colour with many clusters of vertical short, brown hairs that give it a ginger-speckled appearance. The hind wings are well developed as the insect is a strong daylight flier (Jessep, 1981).
R. conicus lays frass-covered eggs on the exterior involucral bracts of immature inflorescences of its host. The larvae hatch and bore into the receptacle of the capitulum, destroying the reproductive surface from which achenes develop. A single larva destroys on average 26 seeds (Sheppard et al., 1994).
Native to Europe and western Asia, R. conicus has been deliberately introduced to Canada in 1968 (Harris and Zwölfer, 1971;Harris, 1984);South America in 1980 (Feldman, 1997);Australia in 1989 (Woodburn and Cullen, 1993;1995);and New Zealand in 1973 (Jessep, 1975;1981) as a biological control agent for thistles in the genera Carduus, Cirsium and Silybum. Introduced populations were collected from different hosts and so included populations from both temperate and Mediterranean climates.
North America has about 90 species of native thistle in the genus Cirsium (USDA, 2013). Susceptibility of these species to R. conicus is related to a) their proximity to exotic host thistle populations on which this weevil is found, and b) the degree to which flowering phenology is synchronous with the reproductive cycle of R. conicus (Russell et al., 2007). A number of rare and threatened native Cirsium species in North America have been documented: these include C. canescens Nutt. (Louda et al., 1990;Arnett and Louda, 2001), C. undulatum Nutt. (Maw, 1982), C. ownbeyi S.L. Welsh (DePrenger-Levin et al., 2010) and C. hillii (Canby) Fernald (Sauer and Bradley, 2008). Turner et al. (1987) listed another twelve species of native Cirsium thistles in California from which R. conicus has been reared. Maw (1982) also found eggs on the native C. flodmanii (Rydb.) in Canada.
The eggs are cemented to the surface of pulses and are smooth, domed structures with oval, flat bases.
Larva and Pupa
The larvae and pupae are normally only found in cells bored within the seeds of pulses. For descriptions and a key including C. maculatus larvae, see Prevett (1971) and Vats (1974).
C. maculatus adults are 2.0-3.5 mm long. The antennae of both sexes are slightly serrate (for details of antennal and sensilla structure see Mbata et al. (1997)). Females often have strong markings on the elytra consisting of two large lateral dark patches mid-way along the elytra and smaller patches at the anterior and posterior ends, leaving a paler brown cross-shaped area covering the rest. The males are much less distinctly marked. In common with other species of Callosobruchus, C. maculatus has a pair of distinct ridges (inner and outer) on the ventral side of each hind femur, and each ridge bears a tooth near the apical end. The inner tooth is triangular, and equal to (or slightly longer than) the outer tooth. A unique chordotonal structure in the fore coxae of adult C. maculatus and C. subinnotatus was described by Ramaswamy and Monroe (1997). The location and ultrastructure of sex pheromone glands in female C. maculatus is described by Pierre et al. (1996).
Several workers have described an active- or flight-form of adult C. maculatus which is apparently more active and is more strongly marked, with a white pygidium (Utida, 1953). The function of this form, which appears in populations as a result of genetic and environmental factors, is not understood.
No particular detection or inspection methods for Callosobruchus spp. have been developed.
The potential exists for the development of population monitoring by use of sex pheromones. The female-produced sex pheromone has been isolated and identified (Phillips et al., 1996);and the behavioural and electroantennogram (EAG) response to pheremonal components by males was recorded by Shu et al. (1996).
C. maculatus is a major pest of cowpeas, green gram and lentils. For a complete list of host plants, see Udayagiri and Wadhi (1989), and Desroches et al. (1997). Host plants vary considerably in their suitability for larval development (Wijeratne, 1998). Alpha-amylase inhibitors prevent development of C. maculatus on a number of legumes (Blanco-Labra et al., 1996;Reis et al., 1997;Ishimoto et al., 1999;Janarthanan et al., 1999) including Phaseolus vulgaris, but not the development of the bruchids Acanthoscelides obtectus and Zabrotes subfasciatus (Ishimoto and Chrispeels, 1996).
There have been many studies of host preference in C. maculatus and its ability to adapt to using hosts less suitable for larval development, for example Huignard et al. (1996);Taheri (1996);Sulehrie et al. (1998). Inheritance of aspects of host plant choice were observed by Messina and Slade (1997).
The eggs are cemented to the surface of pulses and are smooth, domed structures with oval, flat bases.
Larva and Pupa
The larvae and pupae are normally only found in cells bored within the seeds of pulses. For a description and key to larvae of Callosobruchus spp., see Vats (1974).
C. chinensis adults are 2.0-3.5 mm long. The antennae are pectinate in the male, and serrate in the female. The elytra are pale brown, with small median dark marks and larger posterior dark patches, which may merge to make the entire posterior part of the elytra dark in colour. The side margins of the abdomen have distinct patches of coarse white setae, a feature that is shared with C. rhodesianus and C. theobromae. In common with other species of Callosobruchus, C. chinensis has a pair of distinct ridges (inner and outer) on the ventral side of each hind femur, and each ridge has a tooth near the apical end. The inner tooth is slender, rather parallel-sided, and equal to (or slightly longer than) the outer tooth.
Variations in morphological parameters may be induced by different host densities, whether development occurs in pods or in loose seeds (Nahdy et al., 1995), or by population source (George and Verma, 1997).
No particular detection or inspection methods for Callosobruchus spp. have been developed.
The potential exists for the development of population monitoring by use of sex pheromones. The existence of a female sex pheromone in C. chinensis was demonstrated by Honda and Yamamoto (1976), and Gharib et al. (1992), but the pheromone is not commercially available (Phillips, 1994;Plarre, 1998).
C. chinensis is a major pest of chickpeas (Pandey and Singh, 1997), lentils, green gram, broad beans, soybean (Srinivasacharyulu and Yadav, 1997;Yongxue et al., 1998a) adzuki bean and cowpeas in various tropical regions. It also attacks other pulses on occasions, but appears to be incapable of developing on common beans (Phaseolus vulgaris).
See Udayagiri and Wadhi (1989) for a full list of host plants.
Carapace broad (CW/CL c. 2.2-2.3), surface evenly granular, frequently with a short pubescence between granules. Sinuous mesogastric and arched epibranchial ridges as rows of tubercles and a pair of granular elevations in cardiac region present, no other obvious ridges. Nine anterolateral teeth, 1 st acutely triangular, larger than those immediately following, 2 nd to 8 th sharp, 9 th very long, projecting laterally. Front may have four teeth except for inner supraorbital teeth, median frontal teeth usually low and obtuse or even confluent and indistinct, leaving a wide gap between spiniform lateral median teeths. Posterolateral junction of carapace rounded. Merus of third maxilliped with anterolateral corner rounded, not expanded laterally. Chelipeds relatively slender and elongate, smooth or minutely granular, merus usually with three spines on anterior border and a single terminal spine on posterodistal corner, manus with proximal and two distal spines on upper face, upper and outer face with five well-developed costae, under surface smooth, inner surface with median low and smooth costa. Ambulatory legs with merus subquadrate, posterodistal border smooth, propodus elongate, with smooth posterior border, natatorial paddle elongate oval, obtusely angled distally. Penultimate segment of male abdomen longer than broad with evenly converging lateral borders. G1 very long and slender, base with slight basal spur, curved with finely tapering tip and spinules in distal part. Female genital opening located in median part of sternite, elongate with long axis directed anteromesially, thickened cuticle along antero- and posterolateral borders (Apel and Spiridonov, 1998).
R. mangle is normally a small evergreen tree 5-10 m tall with a trunk diameter of 20 cm, but can grow to 20-30 m (and even 50 m) tall, with diameters of 20Ð50(-70) cm, with arching stilt roots 2Ð4.5 m high. Bark grey or grey-brown, smooth and thin on small trunks, becoming furrowed and thick on larger ones. Inner bark reddish or pinkish, with a slightly bitter and salty taste. Twigs stout, grey or brown, hairless, ending in a conspicuous narrow pointed green bud 2.5Ð5 cm long, covered with 2 green scales (stipules) around pairs of developing leaves, and making a ring scar around the twig when shedding. Leaves opposite, crowded at end of twig, hairless, with slightly flattened leafstalks 13Ð22 mm. Blades elliptical, 6-10 cm long, blunt at apex and short-pointed at base, slightly rolled under at edges, slightly leathery and fleshy with side veins not visible, shiny green above, yellow green beneath. Flowers usually 2-4 together at leaf bases on forked green stalks, 4-7.5 cm long, slightly fragrant, pale yellow, about 2 cm across. The bell-shaped pale yellow base (hypanthium) less than 6 mm long bears four widely spreading narrow pale yellow sepals almost 13 mm long, leathery and persistent;four narrow petals 10 mm long, curved downward, whitish but turning brown, white woolly or cottony on inner side;eight stamens;pistil of two-celled ovary mostly inferior but conical at apex, with two ovules in each cell, slender style, and two-lobed stigma. Fruits dark brown, conical, about 3 cm long and 13 mm in diameter, with enlarged curved sepals, remaining attached. The single seed germinates inside the fruit, forming the long narrow first root (radicle), green except for brown enlarged and pointed end, up to 13 mm in diameter. The propagules fall when they are 20-30 cm long (adapted from Duke, 1983;Little and Skolmen, 1989;Hill, 2001;Duke and Allen, 2006).
Spermogonia intraepidermal. Aecia like uredinia. Uredinia epiphyllous (on upper surface of leaf), solitary or a few aggregated on small yellow or purple spots, small, rounded, 0.1-0.3 mm diameter, covered by epidermis, orange-yellow, reddish-brown or yellowish-brown;urediniospores globose, ovate or ovate-ellipsoid, sparsely echinulate, hyaline or pale-yellowish, 22-35 x 16-26 µm, wall 2-3 µm thick. Telia hypophyllous (on lower side of leaf), white, developing in minute, rounded, yellow lesions;teliospores formed on cells emerging through stomata, globose, short-pedicellate, 20-30 x 18-22 µm, walls smooth, thin, hyaline. See Ito (1950) and Hirastuka et al. (1992) for more detailed descriptions.
A. pseudoharengus has an overall silvery colour with a greyish-green back. A black spot at the eye level is directly behind the head. Adults have longitudinal lines that run along the scale lines above the midline of the body. The large scales are deciduous and the lateral line is not well-developed (Scott and Crossman, 1973). Scales on the midline of the belly form scutes, creating a serrated surface (Trautman, 1957). The body is strongly laterally compressed and relatively deep. Eyes are large. The front of the lower jaw is thick and extends past the upper jaw when the mouth is closed. The maxillary extends to below the middle of the eye. A few small teeth are present on the premaxillary and mandible (Scott and Crossman, 1973). There are more than 30 gill rakers on the lower angle of the first gill arch (Trautman, 1957). The single dorsal fin usually has 13-14 rays but may have 12-16. The caudal fin is forked. The anal fin is short and wide with 15-19 rays (usually 17-18). The pelvic fins are rather small and contain 10 rays. The pectoral fins are low on the sides and they usually have 16 rays but may have as few as 14 (Scott and Crossman, 1973). A. pseudoharengus in landlocked populations become stunted;their maximum total length rarely exceeds 200 mm and average total length ranges from 125 to 175 mm (OÕ Gorman et al., 1987;Madenjian et al., 2003). Average length usually increases with the size of the waterbody. In contrast, anadromous A. pseudoharengus can grow to 360 to 380 mm (Collette and Klein-MacPhee, 2002).
Small evergreen tree, 3Ð12 m tall, growing and flowering continuously on fan-like branches;mainline branches becoming erect after leaf fall and so in turn contributing to the formation of the trunk (Troll's architectural model). Branches horizontal, pendant towards the tip, soft-hairy. Leaves simple, ovate-lanceolate, 4Ð14 x 1Ð4 cm, with prominent asymmetry of the leaf blade base;leaf margin serrate, lower leaf surface greyish pubescent. Flowers in 1Ð3(Ð5)-flowered supra-axillary fascicles, hermaphrodite, pentamerous with white petals;number of stamens increasing from 10Ð25 in the first emerging flower in the fascicle to more than 100 in the last;development of the superior ovary declining in the same order, so that from the third and later, flowers do not normally set fruit. Fruit a dull-red berry, 15 mm in diameter, with several thousand tiny seeds in the soft pulp.
IYSV is a tospovirus, similar to the type species of the genus, Tomato spotted wilt virus (TWSV). The virus particles of IYSV are protein-enveloped RNAs and consist of three genomic RNA segments: Large (L), Medium (M) and Small (S). The entire genome codes for six essential proteins via five different open reading frames. The L RNA is negative-sense coding for a polymerase, the M RNA codes for two glycoproteins (GN and GC) and a non-structural protein (NSm), and S RNAs are ambisense and code for the nucleocapsid (N) and the non-structural (NSs) proteins (Pappu et al., 2008). The three RNAs are tightly linked with the N protein to form ribonucleoproteins (RNPs). The RNPs are encased within a lipid envelope (Pappu et al., 2009). Serological divergence exists among tospoviruses, and little cross reaction among antisera is observed (Pozzer et al., 1999). PCR based detection is possible and is used for diagnostics.
Where IYSV infection is suspected, samples should be sent to a diagnostic laboratory for ELISA and PCR testing. The distribution of IYSV within an infected plant is uneven and samples should be taken in close proximity to the lesion (Gent et al., 2006;Pappu et al., 2008).
There is evidence to suggest that iris yellow spot (or a disease causing similar symptoms) may also be caused by Tomato spotted wilt virus (TSWV) or co-infection of TSWV and IYSV (Gent et al., 2006). Mullis et al. (2004) showed that a small proportion of onion plants displaying iris yellow spot-like symptoms were infected with both TSWV and IYSV. This is not surprising as thrips can transmit both viruses (and many others). This phenomenon has not been reported elsewhere and co-infection (TWSV and IYSV) on onion remains speculative.
Symptoms of IYSV consist of eyespot to diamond-shaped, yellow, light-green or straw-coloured lesions (sometimes necrotic) on the leaves, scape and bulb leaves of onion and other Allium host species. In the early stages of infection, lesions appear as oval, concentric rings. Some green islands can be observed within the necrotic lesions. They usually originate around a thrips feeding point. Infected leaves eventually fall over at the point of infection during the latter part of the growing season. Infection at early stages of crop growth results in yield losses. Infection at later stages of development can still cause significant losses due to reduced quality: severely infected fields will senescence prematurely and entire areas will turn brown before they collapse. Symptom severity is dependent on host cultivar, timing of infection, overall health of the host at the time of infection, and environmental conditions (Gent et al., 2004). Du Toit (2005) reported that out of 46 onion cultivars tested, all but 3 had a significant yield decrease and reduced bulb size. The incidence of symptomatic plants generally increases after bulb formation (Gent et al., 2006). IYSV does not always kill its host(s);however, the virus reduces plant vigour, disturbs photosynthesis and reduces bulb size. IYSV infection weakens the plants making them more susceptible to other diseases and pests. IYSV-infected onions grown for seed have reduced seed yield and quality (Evans and Frank, 2009;Pappu et al., 2009).
In 1981, de Avila et al. (1981) described a disease characterized by chlorotic and necrotic, eye-like or diamond-shaped lesions on onion scapes (referred to as ‘sapeca’) in southern Brazil. In 1989, Hall et al. (1993) observed a very similar disease in onion in the USA and detected a tospovirus, which was later shown by Moyer et al. (1993) to be Iris yellow spot virus on the basis of molecular and serological data. In 1998, a new tospovirus was isolated and characterized in the Netherlands from infected iris and leek and named Iris yellow spot virus (IYSV) (Cortês et al., 1998). This virus was subsequently found naturally infecting onion in several major onion-producing states of the USA and around the world (for reviews, see Gent et al., 2006 and Pappu et al., 2009). Gera et al. (1998b) reported that IYSV was responsible for a ‘straw bleaching’ disease on onion in Israel. In 1999, a ‘sapeca’ isolate from Brazil was identified as IYSV on the basis of biological, serological and molecular data (Pozzer et al., 1999). In Israel, Kritzman et al. (2000) reported natural IYSV infection of lisianthus grown in the field. IYSV has now been endemic in south-western Idaho and eastern Oregon in onion, leek and chive seed production fields for over 10 years. Losses caused by IYSV can reach 100% in onion crops, for example, in Brazil (Pappu et al., 2009). However, studies in the Netherlands in 2008 showed that latent infections of IYSV were common in onion crops but did not cause economic damage (NPPO of the Netherlands, 2008).
IYSV has a relatively restricted host range. Edible A llium crops including onion (bulb and seed crops), garlic, chive, shallots, leeks and some cut flower/potted ornamental species including Alstroemeria, chrysanthemum, iris and lisianthus are the most economically important crops affected by IYSV. Wild Allium species and ornamental alliums are also potentially at risk. A range of weed species (Datura stramonium, Nicotiana spp. and Amaranthus retroflexus) can also act as reservoirs.
Six species have been mechanically inoculated in experimental host range trials (Chenopodium amaranticolor, C. quinoa, Datura stramonium, Nicotiana benthamiana, N. rustica and Gomphrena globosa). There is no evidence that these species are infected in the wild. Ben Moussa et al. (2005) reported infection of another three members of the Solanaceae (capsicums, potatoes and tomatoes) but it is unclear if these are natural hosts or were artificially inoculated.
L. latifolium is a perennial herb 1-2 m high, with a creeping root system emanating from a semi-woody crown. Francis and Warwick (2007) describe the underground structures as both rhizomes and roots. Other authors quoted by Zouhar (2004) conclude otherwise, that they are all true roots. It seems likely that both types of structure can occur – short rhizomes (horizontal stems from which buds develop at the nodes) and much longer horizontal roots 10-20 cm deep, on which adventitious buds can develop at any point, especially when fragmented. Other roots can occur much more deeply, even down to 3 m (Zouhar, 2004). A number of erect stems arise from the crown, and are much branched above. Lower leaves are up to 30 cm long by 5-8 cm wide on petioles up to 10 cm long, elliptic-ovate or oblong, finely serrate on the margins and with a whitish mid-rib. Upper leaves are smaller up to 10 cm long, sessile, with entire margins, cuneate base and acute apex. Leaf surfaces may have some hairs, but are generally glabrous, leathery and glaucous.
L. latifolium is an erect, branching perennial native to southern Europe and western Asia. It was accidentally introduced into countries outside of its native range as a contaminant of seeds such as Beta vulgaris. L. latifolium exhibits a wide ecological adaptation to different environmental factors, tolerating a range of soil moisture and salinity conditions, which has allowed it to spread explosively in recent years in wetlands and riparian areas especially in the western USA. L. latifolium thrives in many lowland ecosystems and is extremely competitive, forming monospecific stands that can crowd out desirable native species and a number of threatened and endangered species. L. latifolium alters the ecosystem in which it grows, acting as a ‘salt pump’ which takes salt ions from deep in the soil profile and deposits them near the surface, thereby shifting plant composition and altering diversity.
Strains of P. parmentieri are Gram-negative, rod-shaped necrotrophs which destroy plant tissue components through the activity of plant cell wall-degrading enzymes such as pectinases, cellulases and proteases secreted via Type I or II secretion systems (Chatterjee et al., 1995;Liu et al., 1999;Charkowski et al., 2012) but lack the Type III secretion system (Kim et al., 2009). Pectinases (pectate and pectine lyases, polygalacturonases, methyl- and acyl-) and cellulases play a major role in the virulence of soft-rotting pathogens as they degrade the primary cell walls of infected plants. Proteases are also mentioned as they disrupt host plant protoplasts via degradation of transmembrane proteins (Marits et al., 1999). Effective spread of the pathogen through the plant's vascular system, often referred to as motility of the strain, is essential for the development of disease symptoms (Toth et al., 2003). The efficient production of iron scavenging molecules, siderophores, provides cofactors involved in almost all life-supporting processes (Ishimaru and Loper, 1992).
Symptoms only appear on potato plants. Latent infection is common on potato tubers.
Potato blackleg mainly occurs from plants derived from latently infected seed potatoes. It is more severe when host resistance is impaired. Pathogenesis of P. parmentieri is also temperature dependent. Potato stem diseases generally develop under wet and partially aerobic conditions. Blackleg develops as a consequence of pathogen multiplication in rotting (or latently infected) mother tubers. Infection of seed tubers or stem invasion by P. parmentieri soon after emergence can result in blanking (rotting and death of the whole plant). Stunting, chlorosis and wilting symptoms, caused by restriction of water flow in the xylem vessels following infection, tend to develop at that stage under dry conditions (Pérombelon, 2002).
Potato soft rot during storage is usually a consequence of latent infection of potato crops. The bacteria are sited intracellularly, in lenticels and in wounds, typically beyond the phylloderm layer. Symptoms of soft rot exhibit as tissue maceration with intact skin of potato. A characteristic odor occurs when additional bacteria are present in infected tissue (Perombelon and Kelman, 1980;Pérombelon, 2000).
Pectobacterium parmentieri is a bacterial pathogen of potato present in Europe since the 1960s. The bacterium was earlier classified as Pectobacterium carotovorum. After reclassification of P. carotovorum subsp. carotovorum SCC3193 to P. wasabiae and later on to P. parmentieri, several studies devoted to identification of pectinolytic bacteria in international collections and identification of the strains isolated from infected potato plants have indicated that this bacteria commonly occurs in several regions of Europe, Canada, USA, New Zealand and South Africa. P. parmentieri can cause symptoms of blackleg and soft rot on potato tubers. These diseases are usually a consequence of latent infection of seed potatoes. In the majority of countries pre-basic and basic seed tuber potatoes intended for the production of seed tuber crops should be free of Pectobacterium spp. and Dickeya spp. P. parmentieri is not present on any international or national alert lists.
Spermogonia epiphyllous, numerous, punctate, irregularly and closely aggregated or scattered, minute, at first honey-yellow, then reddish-brown. Telia amphigenous, or on stipules, densely developed over entire leaf surfaces, early naked, confluent, somewhat pulverulent, reddish-brown, ruptured epidermis conspicuous;teliospores broadly ellipsoid or oblong to oblong-ellipsoid, 1-2-septate, 30-50 × 16-35 µm, rounded at apex, rounded or somewhat attenuated at base, slightly constricted at septa, two or three germ pores in each cell, walls 2.0-3.5 µm thick, pale yellow-brown, with three to five rows of warts;pedicels persistent, very short. See Wei (1988) and Hiratsuka et al. (1992) for more detailed descriptions.
There is little published information on this plant pathogenic fungus, which has limited geographic distribution. As hosts exist in other regions of the world with similar environmental conditions, this species may pose a threat to native or agricultural plants if introduced.
P. officinarum is a prostrate, monocarpic herb with a rosette of small, setose, oblanceolate, entire leaves and a single terminal shoot apex. Leaves are elliptic, 3-10 cm long, 1-5-2 cm in width, with distinctive white midvein. The lower leaf surface is covered with a dense layer of stellate hairs, and long, simple eglandular hairs cover both upper and lower leaf surfaces and the leaf margin (Sell and West, 1976). P. officinarum has a single flower head per stem. Florets are yellow, often with a red stripe on the outer face, resembling those of dandelions (Taraxacum spp.). Floral evocation results in the development of one or more axillary buds into stolons that bear further apical meristems at their tips and further dormant buds in the axils of their scale-leaves, which can reach a final length of 10-30 cm, occasionally with a terminal capitulum. Under certain conditions, stolon axillary buds may break dormancy and produce branching stolons. Each branch is potentially capable of developing into a new rosette. These daughter rosettes root adventitiously and their stolon connections atrophy. Daughter rosettes may also develop in situ from the axillary buds of the parent rosette. These growth patterns result in mat-forming growth (Bishop and Davy, 1985;Gottschlich, 1996). Since rosettes are monocarpic (semelparous), the parental rosettes will senesce and die (Bishop and Davy, 1985). The fruit is an achene up to 3 mm long, purple-black at maturity, with a pappus.
P. officinarum is a prostrate herb which has spread rapidly to exotic locations (e.g. New Zealand, North America and South America) after introduction as a garden ornamental or contaminant of agricultural seed. As it continues to be available as an ornamental and can be easily transported by machinery, P. officinarum is likely to spread further. It is an undesirable invader on account of its vigorous growth due to stolon production and wind-dispersed seeds. P. officinarum displaces the inter-tussock vegetation leading to loss of forage and biodiversity.
P. officinarum is generally a pasture or environmental weed, rather than an agricultural weed in crops. However, in North America, P. officinarum is a troublesome weed of fields and pastures (Fernald, 1950;Scoggan, 1979).
Annual or biennial shrub, commonly 1 to 3 m tall but growing up to 6 m and with basal diameters reaching 10 cm under favourable conditions. Leaves are pinnately compound, 5 to 25 cm long and support (5)10 to 20 leaflet pairs. The leaflets are oblong to elliptic, rounded at both ends, mucronate at the apex, base slightly asymmetric, with a silky pubescence below. Stems often with minute prickles and often hidden among the hairs. The racemes have 2 to 8 flowers, peduncle up to 2 cm long, softly silky or pilose;pedicel 3-8 mm long, sparsely silky pilose;calyx 3-5× 3 mm, tube glabrous, teeth triangular, up to 0.7 mm long;corolla yellow, greenish-yellow, or orange. The brown pods that develop after flowering are 10 to 20 cm long, 3 mm broad, cylindrical, linear, long-tipped at apex, containing 20 to 30 seeds. Seeds 2- 3 mm long, 1.5 mm broad, cylindrical, brown to reddish-brown, with tiny blackish spots (Gillett et al., 1971;Ipor and Oyen, 1997).
S. sericea is a fast-growing, short-lived woody shrub of frequently disturbed areas. It is commonly planted in agroforestry systems to be used as green manure, animal forage, and for soil improvement (Ipor and Oyen, 1997). However, each plant is able to produce large amounts of seeds, allowing the species to escape from cultivated areas and colonize new habitats. Seeds may survive in the soil for several months (up to one year) waiting for suitable conditions to germinate. Once established in new areas, S. sericea grows forming dense thickets and competing aggressively with grasses and native vegetation (Francis, 2000). It is included in the Global Compendium of Weeds as a natural and agricultural weed (Randall, 2012).
The morphology of all developmental stages of C. ohridella has been studied mainly by Deschka and Dimic (1986), Skuhravý (1998) and Sefrová and Skuhravý (2000).
The eggs are white and 0.2-0.4 mm.
There are four, occasionally five, instars of feeding larvae and two instars of spinning larvae. Instars of feeding larvae differ by length and by width of the head capsule (Sefrova and Skuhravy, 2000).
First-instar larvae are 0.5 mm long;head capsule is 0.1-0.17 mm wide.
Second-instar larvae are 1.2 mm long;head capsule is 0.2-0.3 mm wide.
Third-instar larvae are 2.1 mm long;head capsule is 0.36-0.46 mm wide.
Fourth-instar larvae are 3.5 mm long;head capsule is 0.5-0.66 mm wide.
Larval morphology of C. ohridella corresponds to that of the subfamily Lithocolletinae (Kumata, 1963). The body is distinctly constricted between the segments which appear to be convex laterally. Tergites and sternites are formed from extensively sclerotized plates, which enable the caterpillars to move within the mine. The mouthparts, the labrum and labium, are massive, shield-shaped;the flat sickle-shaped mandibles move horizontally. The thoracic legs and the ventral and anal prolegs are completely reduced. The width of the head capsule of the two spinning instar larvae does not change from the fourth feeding instar larva. Mouthparts are complete and the antennae, maxillae and maxillar palpi and spineret are present (Sefrova and Skuhravy, 2000).
The pupa is brown and is 2.9-4.5 mm long (3.7 mm on average). Freise and Heitland (1999) describes a method to distinguish between male and female pupae.
The body is 4-5 mm long. The moth is a rich brown colour with bright white chevrons edged with black.
In spring, adults emerging from overwintering pupae can be detected by pheromone trapping or by inspecting the trunks of Aesculus hippocastanum for moths. Later in the season, mines are usually very numerous and easily detected on the leaves.
Larvae of C. ohridella form blotch mines and develop in the parenchyma tissue of leaves of Aesculus hippocastanum. The mines start off small and yellow, later turning brown. Eventually the mines may cover the entire surface of the leaflets, especially from July on, when the second and third generations develop. At sites where dead leaves containing overwintering pupae are not removed in the autumn, trees are usually totally defoliated, year after year.
Cameraria ohridella probably originates from remote natural stands of the European horse-chestnut, Aesculus hioppocastanum in Greece, Albania and Macedonia. It was first observed attacking ornamental horse-chestnut trees in Macedonia in the 1970s, then in Serbia in 1987 and Austria in 1989, from where it spread to most of Europe. Since then, in all invaded regions, outbreaks have continued unabated, causing aesthetic damage to horse-chestnut, one of the favourite ornamental trees in European cities. The fast dispersal of the moth in Europe is attributed mainly to human transport. Cars, lorries, trains and other vehicles may carry adults and overwintering pupae in dead leaves. The moth is listed in the 100 worse invasive species in Europe in the DAISIE database (DAISIE, 2009).
C. ohridella lives primarily on the leaves of Aesculus hippocastanum, but successful development is also occasionally observed on Acer pseudoplatanus and Acer platanoides. It also develops on some species of the genus Aesculus, but not on others (Skuhravý, 1998;Hellrigl, 2001;Freise, 2001). Freise et al. (2003a) and Kenis et al. (2005) carried out screening tests on most of the world Aesculus spp. and several Acer spp. to assess the present or potential host range of C. ohridella. The two most suitable hosts were A. hippocastanum and the Japanese horse-chestnut A. turbinata, whereas successful development also occurred on the American species A. glabra, A. sylvatica and A. flava (= A. octandra). In contrast, it did not develop successfully on the Asian A. chinensis, A. assamica and A. indica and on the American A. pavia, A. californica and A. parviflora. Larvae also developed successfully, but often failed to pupate, in the North American A. circinatum and, occasionally, in the European A. pseudoplatanus, A. tataricum and A. heldreichii, and the Asian A. japonicum.
C. elastica is an androdioecious tree that can grow up to 30 m tall with a diameter at breast height of up to 60 cm. In a cosexual plant, staminate and pistillate flowers occur in different inflorescences. Also, the staminate inflorescences in male and in cosexual plants differ (Sakai, 2001). The plant produces abundant milky sap when slashed and yields latex, which used to be used in the rubber industry. C. elastica has spreading or drooping branches, the young ones woolly-hairy. The leaves are coarse, densely hairy on both sides, short-stemmed, arranged in two rows, the blade oblong, broadest in the upper half, 20-45 cm by 7-15 cm, base heart-shaped and tip pointed, with approximately 18 pairs of prominent veins. Inconspicuous female flowers in short-stemmed heads at leaf axils develop into fruit about 4 cm in diameter, consisting of a cluster of many red individuals about 2 cm long, with more or less sweet, edible pulp (PIER, 2013).
Individuals of C. elastica can easily be observed along forest edges, which is its preferred habitat.
C. elastica is a deciduous latex-producing tree native to southern Mexico, Central America and parts of South America (Sakai, 2001). Owing to its importance as a source of latex and the invention of vulcanisation in 1839, C. elastica was introduced outside its native range to provide material for the growing rubber industry (Wright, 1912). The species is regarded as invasive in Samoa, American Samoa, French Polynesia, the Cook Islands, Queensland, Christmas Islands, Singapore, Cuba, Vanuatu, Mayotte and Tanzania, where it poses significant threats to native forest ecosystems (Richard, 2007;Dawson et al., 2009;PIER, 2013). It has prolific seed production and high germination, produces fruits which are attractive to many forest dwelling frugivores such as primates, squirrels and birds that are capable of dispersing seeds over long distances and is listed as a weed threatening forest ecosystems.
Development or developing may refer to: