Any sap-sucking member of the insect family Aleyrodidae (order Homoptera).
Nymphs are flat, oval, and usually covered with a cottony substance. Adults, 0.08–0.12 in. (2–3 mm) long, are covered with a white opaque powder and resemble moths. Whiteflies are abundant in warm climates, on houseplants, and in greenhouses. The greenhouse whitefly is one of the most abundant and destructive members of the family. The citrus whitefly and citrus blackfly damage fruit and other crops by sucking sap and producing honeydew, a by-product of digestion on which grows a sooty fungus that ruins fruit and reduces the host plant's ability to photosynthesize.