Cotton - Whiteflies
Description
Most species have uniformly dull white wings, however, the banded-wing whitefly has two dark bands on each wing. Adult sweet potato whiteflies are indistinguishable from greenhouse whiteflies in the field, but upon inspection under magnification the pupae lack projecting filaments. Whiteflies appear to be tiny moths. Their scales, which are pure white and finely powdered, come off on clothing and may be seen on parts of cotton. Fully developed, they are only 1/16 inch long. The immature stages, or larvae, resemble miniature scale insects.
Damage
As with all sucking insects, whiteflies cause both direct and indirect damage. Cotton is directly damaged by larval and adult stages as the pests suck sap from the plants. Premature defoliation is reflected in reduced boll development and lower yields and quality. Whiteflies also indirectly damage cotton by secreting honeydew and creating fertile conditions for fungal growth (sooty mold), interfering with plant's photosynthesis and lowering lint quality. Whiteflies also act as vectors of plant viruses, causing further damage to the crop.
Life cycle
Whiteflies can be active all year. Their eggs are laid on the undersides of leaves of the 60 or more host plants they may attack. Eggs hatch in five or six days after being oviposited. Emerging larvae crawl short distances, and become firmly anchored to the underside of the leaf when they insert their feeding tubes into the plant tissue. The larvae feed five or six days, going through about three stages or molts. The pupae do not feed, but they continue to develop for several days until the winged adult emerges. In summer, generation time may as short as 15 to 18 days. In winter, the cycle may require 45 or more days. The sweet potato whitefly requires about 15 to 20 days completing its life cycle in the summer. Most of this time is spent as a larva. Populations can increase up to ten׳ fold in two weeks. Tremendous population explosions occur when natural enemies are destroyed.