Description
Whiteflies are tiny (1/12 inch long), winged insects that are found mainly on the undersides of leaves. When the plant is touched, insects flutter rapidly around it. Whiteflies belong to a family of insects called Aleyrodidae, which means flourlike. The wings of the adults are covered with a white powdery substance. Whiteflies are able to survive outdoors only in the southern parts of the United States. Their population may build up to tremendous numbers during the growing season. Whiteflies may also infest outdoor plants in colder climates. Infestations come from migrating whiteflies and infested greenhouse-grown plants placed in the garden. Some whiteflies serve as disease vectors, and many produce copious amounts of honeydew.

Control
Whiteflies have 5 stages of development, and each stage has a different tolerance to insecticides. The minute eggs are resistant to most insecticides. The crawlers that hatch from the eggs can be controlled by contact insecticides, such as a horticultural oil spray or an insecticide containing malathion. The crawlers settle to feed, inserting their mouthparts into plant tissue. They soon lose their legs and take on the appearance of a scale insect. This stage is resistant to contact insecticides, but can be controlled on ornamentals by insecticides--such as acephate--that act systemically. All life stages may be present at the same time, but a single application of insecticide affects only susceptible stages. Sprays must be applied at least 3 times at intervals of 4 to 6 days to achieve control.

Related Links
Insecticides

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