Adult whiteflies measure about 1 mm and are typically covered with a white waxy powder. Two species commonly occur in greenhouses: the greenhouse whitefly (Trialeurodes vaporariorum) and the tobacco whitefly (Bemisia tabaci).

Adults of the latter species can be mainly distinguished by the wings which they hold closer to their body than Trialeurodes adults do. Moreover, Bemisia pupae have a more pointed and irregular shape, with less and shorter wax threads, and a more yellowish colour than Trialeurodes pupae.

The female whitefly deposits its oval shaped eggs of 0.2 mm on the underside of young leaves at the top of the plant. The larva that hatches is first mobile during a few hours to search for a suitable place on the leaf to settle. Later on in the subsequent larval stages and pupal stage, it does not move anymore. The four larval stages look very similar, but differ clearly in size.

After the fourth larval stage is formed, an adult whitefly finally emerges from the pupa through a T-shaped exit hole. On tomato, development from egg to adult takes 20 days at 27°C (80.6°F) or 38 days at 17°C (62.6°F), but on other host plants this can be quite different. Also, fertility depends on temperature and host plant. At 17°C (62.6°F) a female lays 100-150 eggs on tomato, 250-300 eggs on cucumber and 450-600 eggs on eggplant.

Both larvae and adults suck plant juices. Secretion of honeydew fouls the leaves and the fruits, which then become unmarketable. Often moulds (Cladosporium spp.) grow on the honeydew, which hampers photosynthesis and respiration of the plant. Moreover, whiteflies can transmit several viruses.