Whitefly is the name given to a variety of bug-like insects that belong to the Aleyrodidae family. They are small members of the Hemiptera (‘true bugs’) order that feed on the underside of the leaves of plants. They damage host plants by boring into the phloem (the tissue that transports sugars around the plant). The plant loses turgor as a result, and it also reacts to the toxic saliva of white flies.
Because white flies live together in large groups they can quickly decimate a plant totally. Their impact can be so serious that when someone brushes against a leaf a swarm of white flies takes off, flutters about before re-landing on the underside of the leaf again. They also excrete honeydew, which can become a food source for moulds, while the stickiness of the stuff can also become a terminal problem for some plants, such as cotton.
They have a remarkably adapted form of metamorphosis. Life begins with the immature pre-adult stages when the flies are mobile individuals before rapidly attaching themselves to a plant. The stage before adult is called a chrysalis, even though technically it is not the same as the real pupation undergone by holometabolic (complete metamorphosis, as experienced by bees and butterflies) insects.
One of the best-known species is the Greenhouse whitefly (Trialeurodes vaporariorum) which is an insect pest in greenhouse horticulture. Other well known species include the silverleaf or sweet potato whitefly (Bemisia argentifolii) and the Banded winged whitefly (Trialeurodes abutiloneus).
Combating whitefly is difficult. The Greenhouse whitefly has developed resistance to many pesticides. The United States Department of Agriculture recommends prevention of infestation by using a biological agent when possible. They advise the application of yellow, sticky traps to detect the presence of whitefly and only applying insecticide selectively.
The whitefly can also be combated with the help of its natural enemies such as the ichneumon family of parasitic wasps. The predator bug hunts whitefly for food, and the larvae of lacewings also attack whitefly and suck them empty.