Egg -The spherical egg ranges in color from transparent and colorless to opaque straw yellow.
Larva- The six-legged larva is colorless to pale green or yellow.
Nymph-Similar to the adult except in size, the pale green to brownish-green nymph has eight legs. Large spots of black may develop on each side.
Host Plants -Twospotted spider mites have been reported on over 180 host plants, which include over 100 cultivated species. Violets, chickweed, pokeweed, wild mustard, and blackberry are common foci from which infestations develop on nearby crops.
Damage -Twospotted spider mites pierce the epidermis of the host plant leaf with their sharp, slender mouthparts. When they extract the sap, the mesophyll tissue of the leaf collapses in the area of the puncture. Soon a chlorotic spot forms at each feeding site. After a heavy attack, an entire plant may become yellowed, bronzed, or killed completely (Color Plate 4II). The mites may spin so much webbing over the plant that it becomes entirely covered.
Life History -Twospotted spider mites occur as important pests on more crops than any insect pest in the Southeast. Though insects and mites are in a group called the Arthropoda (meaning jointed foot), because jointed legs are common to both, spider mites are not actually insects. Being more closely related to spiders, they derive their name from the thin web that some species spin. In the Southeast, twospotted spider mites overwinter as adults in the soil or on weed hosts such as violets and hollyhocks. In mild winter weather, twospotted spider mites continue to feed and lay eggs, although development in the winter is much slower than in the summer. Six legged larvae hatch from the eggs. They develop into eight legged nymphs, which pass through two nymphal stages. After each larval and nymphal stage, there is a resting stage. The adults mate soon after emerging from the last resting stage, and in warm weather the females soon lay eggs. Each female may lay over 100 eggs in her life and up to 19 eggs per day. Development is most rapid during hot, dry weather. A single generation may require as many as 20 or as few as 5 days to reach adulthood and begin producing offspring.
The resting stages and eggs of the twospotted spider mite are more tolerant to pesticides than the motile forms. Consequently, a second application of pesticide may be necessary at a 4- or 5-day interval in hot weather (a 7- to 10 day interval in cool weather) to kill those mites that may have survived the first application. For specific chemical controls, see the current state extension service recommendations.
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