Adults of greenhouse whitefly have their wings in horizontal position, somewhat overlapping. This distinguishes them from adults of tobacco whitefly that have their wings in an angle, like a shelter. Eggs are whitish shortly after deposition and turn black within 2-3 days. Pupae are white and translucent, having a crown of waxy hairs on their surface. The leaf surface around the pupae is covered with lots of honeydew. Only young instars are able to move around on the leaves. As soon as they have found a proper place to stay they will settle there and stay for the rest of their lives. First and second instars look like pale yellow, translucent and flat scale covers (resembling some armoured scale species), hardly visible by naked eye. During 4th instar and shortly before becoming adult more details of the adult fly become visible, such as their composed eyes. The insects swallow and start to get free from the leaf surface. This stage may be called the pupal stage.
Distribution and crop damage:
Adult whiteflies often rest on the underside of young leaves in the top of the plant. Eggs are deposited at the underside of the leaves. Instars also prefer the underside of leaves. All developmental stages except from eggs and pupae cause damage to the crop. They suck from plant tissue, feeding themselves with the phloeem. A secondary product of their feeding activity is deposited on the leaves as honeydew. This sticky substance causes serious damage since it is a food source for the black sooty mold fungus. Leaves and whole plants turn black because of this and harvest may not be possible anymore. The third and maybe most important damage tht whiteflies cause is their potential to transfer plant viruses. Most infested crops are vegetables, such as cucumber, potato and tomatoes. Other crops such as herbs may also become infested, offering the pest a chance to survive in the greenhouse, also when the crop has been harvested.
lifecycle greenhouse whitefly:
- development time egg - adult on tomato at 27 oC: 20 days; at 17oC this takes 38 days.
- fecundity depends on temperature and crop type
- females may lay around 100 eggs on tomato, 200 on cucumber and 300 on egg plant
- after hatching of adults a T-shaped crack is visible in the pupal skin
host plants greenhouse whitefly:
- ornamental potplants
- egg plant
Products against greenhouse whitefly
Encarsia formosa + Eretmocerus eremicus: