Twospotted Spider Mite
Egg - The egg is spherical, minute, and transparent when first laid. Just before hatching, it becomes straw colored or yellowish-green.
Larva - The six-legged larva, not much bigger than the egg, is colorless except for carmine eyes.
Nymph - There are two nymphal stages which are difficult to distinguish. Both are pale green, oval, and eight-legged. The pair of dark spots are visible at this point of development.
Host plants - Twospotted spider mites have been found on over 180 host plants including at least 100 cultivated species. Violets, chickweed, pokeweed, wild mustard, and blackberry are common hosts from which infestations spread to crops nearby.
Damage - The spider mite is a frequent minor pest in cotton fields near sources of infestation (brush, weeds, clover, and peanuts for example). Yield reduction is greater when infestations develop in the early squaring stage than in late stages of plant growth. Feeding usually occurs on the underside of the leaf where the mites pierce the epidermis and extract the sap. Infested foliage soon assumes a whitish or bronze appearance. Lightly infested leaves have pale blotches or spots showing through the leaf; heavily infested leaves turn completely pale and dry up, or their edges turn reddish-brown. The entire plant may die. The undersurfaces of the leaves usually have silken webs over which the mites crawl, though a heavily infested plant may have webs all over it. Close examination reveals adult mites on the leaves.
Life history - Twospotted spider mites overwinter as females resistant to low temperatures. In mild winters, they may continue to feed and lay eggs. During summer, many generations may develop; the number of eggs laid depends largely upon temperature. In 3 to 19 days eggs hatch into six-legged larvae, which develop into eight-legged nymphs. There are two nymphal stages: protonymphs and deutonymphs. After the larval and each nymphal stage, there is a resting stage. In warm weather, the females soon begin laying eggs; each female produces up to 19 eggs per day and up to 100 eggs in total. Development is rapid in hot, dry weather. One generation may mature in as few as 5 days or as many as 20.
Spider mites are distributed over a field in two ways: (1) migration of females from a heavily infested area to a lightly infested one, and (2) natural or mechanical transportation of mites (by wind, mammals, and man or his machinery) from an infested area to an uninfested one. Man often spreads the mite inadvertently by walking from an infested area to an uninfested area, carrying mites on his pants legs. Therefore, known "hot spots" should be investigated last.
Several available miticides provide effective chemical control. Since recommended miticides do not act as ovicides, a second application is often advised 5 to 7 days after the first. Currently recommended miticides are given in the North Carolina Agricultural Chemicals Manual.
