Adult Females
The morphology of adult females was described in detail by Ezzat and McConnell (1956), McKenzie (1967), Entwistle (1972), Cox (1989), Cox and Freeston (1985) and Padi (1990).
The external diagnostic characters include 18 pairs of short, stout wax filaments along margins, of which the anal and two preceding pairs are slightly longer than the rest but less than 20% of body length. Dorsum covered with fine mealy wax with a slightly darker, longitudinal, median stripe from first thoracic to mid-abdominal segments. Body colour beneath wax is usually yellow to peach pink. Antenna 8 segmented. Authoritative identification requires microscopic study of slide-mounted females;Sirisena et al. (2013) provided a method for preparation of slide mounts of adult females.
Body of slide-mounted adult female oval, 1.6-3.2 mm long, 1.2-2.0 mm wide (Cox, 1989). Body margin with 18 pairs of cerarii, each cerarius with two conical setae except for the pre-ocular pair which may have one or three setae each. Legs elongate;hind trochanter + femur 220-350 µm long;hind tibia + tarsus 260-420 µm long. Ratio of hind tibia + tarsus to hind trochanter + femur 1.1-1.3;translucent pores present on hind coxae and tibiae. Circulus quadrate, width 120-200 µm. Cisanal setae shorter than anal ring setae. Anal lobes moderately developed;anal lobe cerarii each situated on a small, moderately sclerotized area;venter of each anal lobe with sclerotized anal lobe bar bearing apical seta and bar seta.
Venter
Multilocular disc pores present around vulva, in single or double rows across posterior edges of abdominal segments III-VII, in single rows across anterior edges of segments V-VII, in marginal groups on abdominal segments IV-VII and sometimes a few pores scattered over median area of the thorax and head, but no more than a total of six pores behind the front coxae. Oral collar tubular ducts of two sizes: smaller ducts in sparse rows across median areas of abdominal segments I-VII;larger ducts in marginal groups of variable size around entire venter including head and thorax, and scattered over median area of thorax.
Dorsum
Multilocular disc pores absent. Tubular ducts without rims, slightly larger than the larger ducts on venter, often adjacent to some cerarii. One or two ducts sometimes present on median areas. Simple pores present of two sizes, smaller pores smaller than the smaller size on the venter, scattered over entire dorsum;larger simple pores, each about twice the size of a trilocular pore, present in small groups along mid-line of thoracic and anterior abdominal segments. Setae short and flagellate, longest seta on abdominal segments VI or VII 30-35 µm long.
Adult Males
Males each have a single pair of wings and no mouthparts. They cannot be authoritatively identified at present. Detailed descriptions of the morphology of the adult male are available in Giliomee (1961), Afifi (1968) and Afifi et al. (1976).
Although generally cryptic in nature, P. citri can be easily detected on fruits and inflorescences. On cocoa, it can be readily detected on the surface of pods, where it usually forms large colonies. Colonies in terminal buds, bases of leaf petioles, points of attachment of chupons [suckers], fruits and pods, and the bark of trees can be detected using a hand lens or, in the case of terminal buds, by teasing them apart and inspecting them under a dissecting microscope. On Citrus, the area underneath the calyx and the peduncle of the fruit provides a good hiding place (Meyerdirk et al., 1981). P. citri can also be detected in the field by the presence of ants and sooty moulds that develop on excreted honeydew (Gausman, 1974) and by wilt of plant parts such as leaves, inflorescences and fruits or berries.
Related invasive species
- Planococcus citri
Related Farm Practice
- Depletion
- Hosts
- Rest
- Feeding
- Groups
- Identification
Planococcus citri is a highly polyphagous, adaptable mealybug that can feed on many host plants in a variety of conditions, and can reproduce rapidly. It has been reported on over 200 host-plant species belonging to 191 genera and 82 families, and can seriously damage many crops, particularly citrus and glasshouse tomatoes. It is known to transmit some plant virus diseases like Cacaoa swollen shoot virus. The mealybug is of Old World origin, but its polyphagy has facilitated its spread about the world by human transport of infested plants over many years, and it is now established in in all the temperate and tropical zoogeographic regions, and lives under glass in higher latitudes. Its small size and cryptic habits makes it difficult to detect and identify at plant quarantine inspection. The increase in international trade in fresh plant material in recent years is facilitating its continued spread.
P. citri feeding leads to general wilting due to sap depletion. On cocoa, flower stalks, buds and young pods are attacked (Entwistle, 1972). In Taiwan, infested immature coffee berries become deformed and drop to the ground (Moriyama, 1941).
P. citri infestation also causes indirect physical damage because sugary honeydew excreted by the mealybugs fouls plant surfaces, giving rise to sooty moulds (Gausman and Hart, 1974) that block light and air from the leaves, inhibiting photosynthesis.
Citrus mealybug is the second most important vector of several strains of Cacao swollen shoot virus;symptoms include leaf chlorosis, root necrosis, root and stem swellings and dieback (Posnette, 1941;Cotterell, 1943).
P. citri is polyphagous and occurs on a wide range of flowering plants, having been recorded on over 200 host species belonging to 191 genera in 82 families (García et al., 2016).
In the tropics, it occurs mainly on the aerial parts of crops such as cocoa, bananas, tobacco and coffee and on wild trees such as Ceiba pentandra and Leucaena (Strickland, 1951a,b;Le Pelley, 1968;Entwistle, 1972). In Ghana, P. citri has been recorded on about 54 host plants, including cocoa, cola, pineapples, Musa paradisiaca and others within the families Bombacaceae, Euphorbiaceae, Fabaceae, Moraceae, Rubiaceae, Solanaceae, Sterculiaceae, Tiliaceae and Urticaceae (Strickland, 1951a;Padi et al., 1999). Hargreaves (1937) cited Anisophyllea laurina as an alternative food plant in Sierra Leone.
In the South Pacific region, P. citri has been recorded on 20 host plants, including Brassica, Ceiba, Citrus, cocoa, Cyrtosperma, Cucurbita, Gardenia, Inocarpus, Ipomoea, Leucaena, Morinda, Ocimum, Psidium, Pueraria and Solanum spp. (Williams and Watson, 1988). Its host plants in Australia include pumpkins in New South Wales;Clerodendrum, Coleus, Croton and Erythrina species in hothouses, and Ceratonia, Siliqua and Veronica species in the open in Adelaide (Brooks, 1957);and pineapples (Carter, 1942), Vitis vinifera and passionfruits in Queensland (Williams, 1973;Murray, 1978b).
In India, P. citri occurs on mandarin orange (Amitava Konar, 1998) and has been recorded for the first time on soyabean (Jadhav et al., 1996).
In temperate regions, P. citri mainly occurs on greenhouse plants such as Coleus, ferns and gardenias, but also occurs outdoors under summer conditions on Citrus, grapes, figs, taro, date palms and potatoes (Bivins and Deal, 1973;Gibson and Turner, 1977). It mainly attacks Citrus but not grapes in the Mediterranean region (Cox, 1989) and California. In the former Soviet Union, it occurs on over 20 species of plants, notably Citrus, figs and pomegranates (Niyazov, 1969). In Turkmenistan, pomegranates are most liable to heavy infestation. It occurs on Areca sp. and a wide range of greenhouse ornamental plants in Korea (Paik, 1972) and Bulgaria (Tsalev, 1970).
In Texas, USA, P. citri has been recorded on the milk vine Cynanchum unifarium [ Cynanchum racemosum var. unifarium ] (French and Reeve, 1978). Host plants in India include Macadamia ternifolia (Wysoki, 1977).