The thorax is packed with muscles for the wings and legs which arise from that section. Some viruses are entomopathogens . The intermediate host , of disease-producing organisms, which conveys them. These are very small insects , seldom more than 2 or 3 mm in length, that resemble tiny moths. The adults of both sexes are winged and are usually covered with a white dust or waxy powder.
First instars are active and called crawlers.
Later instars are sissile and look like scales. They have piercing-sucking mouthparts which they use to suck sap from the leaves of plants. They also excrete large mounts of honeydew which sooty-mold grows upon. Some whitefly species are serious pests of cultivated plants. See Honeydew .