Whiteflies derive their name from the powdery white wax covering the adult’s wings and body. Adults are tiny (less than 2mm long) insects with yellowish bodies and whitish wings. They usually occur in groups on the undersides of leaves. The most common species in horticultural farming is the greenhouse whitefly, Trialeurodes vaporariorum.
Adults generally feed on young leaves close to the growing point of the plant, and lay eggs there on the underside of the leaves. After hatching, the eggs undergo four stages before becoming adults. The first instar, or nymphal stage, hatches in 5-10 days. Sometimes called crawlers, whiteflies at this stage are flat and scale-like and crawl around for a short while before becoming immobile. The second and third nymphal stages are followed by the fourth, or pupal, stage. The adult emerges from the pupal stage. Development is temperature and crop cultivar dependent and populations can build up quickly in situations where natural enemies are destroyed and weather is favourable.
Whiteflies suck phloem sap. Large populations can cause leaves to deform, turn yellow, appear dry, or fall off plants. They also excrete honeydew, so leaves may be sticky or covered with black sooty mold. The honeydew may also attract ants, which interfere with the activities of natural enemies that may control whiteflies and other pests.