Whiteflies are moth-like insects belonging to the family Aleyrodidae. Whiteflies are not true flies but belong to the order Hemiptera (true bugs). Together with aphids and scale insects, they belong to the division Sternorrhyncha. In protected crops, the most common species are the greenhouse whitefly, Trialeurodes vaporariorum, and the tobacco whitefly, Bemisia tabaci. In outdoor crops whiteflies cause significant damage, variety of crops such as tomato, cabbage, potato and citrus.
Life Cycle
Adult females live up to six weeks, and can produce up to 200 eggs, usually laying them on new plant growth on the undersides of leaves. Whiteflies undergo six distinct developmental stages: egg, first, second, third, and fourth larval instars, and finally, the adult stage. The late fourth larval stage is often called a 'pupa.' The eggs are laid upright, spindle-shaped, and attached to a short pedicel. Upon hatching, the young larvae, known as 'crawlers,' have well-developed legs and antennae and actively seek a suitable spot on the leaf to feed.
Once they find a feeding spot, they remain there for the rest of their larval development. The fourth larval instar, when the red eyes of the adult whitefly become visible, is also referred to as a 'pupa.' Whitefly species are most easily distinguished at the pupal stage. The adult whitefly emerges from the hardened cuticle of the pupa through a characteristic T-shaped opening created by splitting along pre-existing seams on the upper surface. Newly emerged adults have two pairs of transparent wings, which later become covered with a white, waxy powder, giving the insect its characteristic appearance. Adult whiteflies typically reside on the underside of young leaves where they lay their eggs.
Preferences
The greenhouse whitefly and tobacco whitefly can thrive on a wide range of different host plants from all manner of families. Whitefly can appear on various vegetable crops, including tomato, cucumber, aubergine, courgette, bean, and pepper as well as potato. A whole host of ornamental crops, including rose, gerbera, hibiscus, and poinsettia, are also not safe from whitefly.
The problem inside the greenhouse is more acute than outside, as temperatures inside tend to be higher. This stimulates the development of the infestation. In addition, rain and wind are factors that affect outdoor areas, lowering the risk of infestation.
The spread of whitefly
Depending on the species, whitefly development of the whitefly population is optimal at temperatures between 20 and 30°C. Flying adult insects spread the infestation, but attacks from outside the greenhouse are also a threat.
The greenhouse whitefly tends to spread over the plant vertically, consi