Spider mite
From Wikipedia, the free encyclopedia
Spider mites are members of the arachnid class (order Acari) and the family Tetranychidae, which includes about 1600 species. They generally live on the leaves of plants, where they may spin protective silk webs, and they can cause damage by puncturing the plant cells to feed.
Spider mites are less than 1 mm in size and vary in color. They lay small, spherical, initially transparent eggs and many species spin silk webbing to help protect the colony from predators; they get the 'spider' part of their common name from this webbing. Hot, dry conditions are often associated with population build-up of spider mites.
The best known member of the group is Tetranychus urticae (the glasshouse red spider mite, or two-spotted spider mite), which is common in tropical and warm temperate zones, and in glasshouses. Other speices which can be important pests of commercial plants include Panonychus ulmi (fruit tree red spider mite) and Panonychus citri (citrus red mite).
Spider mites, like hymenopterans and some homopterous insects, are arrhenotochous: females are diploid and males are haploid. When mated, females somehow avoid the fecundation of some eggs to produce males. Fertilized eggs produce diploid females. Unmated, unfertilized females still lay eggs, that originate exclusively haploid males.
