ABSTRACT
Fossil evidence indicates that insect wings may have evolved from gills used by aquatic forms for ventilation and swimming. The number of times an insect molts varies; in most insects there are four to six molts, but silverfish and some mayflies may undergo 10 or more. The instars of insects with this type of metamorphosis are called nymphs. Nymphs closely resemble the adult insect except in size and the development of wings and reproductive organs. The pest status of insects in the agricultural and human environment is usually based on the damage done by the feeding of the adult or immature stages. Insect mouthparts are located on the ventral or anterior part of the head, and they vary considerably with different insect groups. Mites are found in nearly every habitat of the world. Many species are important as vectors of human diseases and those of domesticated animals, pets and crops.
