Eggs
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.
Larvae
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.
Light Traps
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.
Feeding Traps
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).
Sexual Traps
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.
Scouting
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.
Modelling
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).
Related invasive species
- Lobesia botrana
Related Farm Practice
- Light
- Feeding
- Development
- Behaviour
- Protection
- Natural enemies
- Damage
- Vineyards
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 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).
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.