Whiteflies feed exclusively on leaves, nearly always occurring on the undersurface. They suck juices from the plants and also excrete large quantities of honeydew in which sooty mold grows. Leaves will be sticky if there are many whiteflies feeding on the leaves above them and may turn black with sooty mold which grows on the honeydew.
The most common whitefly found on Florida vegetables is called the silverleaf whitefly (http://edis.ifas.ufl.edu/in286) because of the effect its feeding has on squash leaves.
Feeding by the immature stages or nymphs can also result in white areas in tomato fruits, streaking of pepper fruits, and blanching of broccoli stems.
Whiteflies are not flies but are distant relatives of aphids and leafhoppers and, like them, feed on plant sap with piercing- sucking mouthparts. Whiteflies can spread some plant viruses, such as tomato yellow leaf curl virus and bean golden mosaic virus.
The adult is a very small (less than 1/16 inch long) and has white wings dusted with a waxy substance. It holds its wings like a tent over its yellow body (Figure 26). It lays its eggs on the lower surface of leaves of many plants, including tomatoes, eggplant, melons, cucumbers, squash, okra, beans, cabbage, and broccoli. Except for a very brief time after hatching, the nymphs cannot move on the plant and look like clear or pale yellow scales. Regular applications of insecticidal soap may help keep whiteflies under control.
Tiny wasps also attack the whiteflies. Flowers planted around and in the garden may help these wasps and other beneficial insects survive by providing a source of nectar. Other general purpose garden insecticides that kill on contact may also be helpful but will harm the beneficial insects. Because the insects are found on the lower leaf surface, sprays must be directed there in order to be effective. It will be very important to wash greens before consumption if using any type of insecticide.