TWOSPOTTED SPIDER MITE

Steven D. Frank & S. Bambara, Extension Entomologists

General Information

Twospotted spider mites can be rusty green, greenish amber or yellow and unlike insects, these arthropods have eight legs instead of six. Overwintering females are red or orange. These mites have two (sometimes four) black spots on top. They are very small, but still visible.

The eggs vary from transparent and colorless to opaque straw yellow. The first stage larva is colorless to pale green or yellow and has only six legs. Nymphs are similar to adults except in size. Nymphs are pale-green to brownish-green and have eight legs. Large spots of black may develop on each side.

Biology

Twospotted spider mites are widely distributed in the United States and feed on over 180 host plants, including over 100 cultivated species. Violets, chickweed, pokeweed, wild mustard and blackberry are common sources from which mites spread to nearby plants. 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. The mites may spin so much webbing over the plant that it becomes entirely covered. 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 before it begins producing offspring.

Monitoring:

Twospotted spider mites occur as important pests on more crops than any insect pest in the Southeast.  Roses, daylilies, hollyhock, marigold and other herbaceous flowers are common hosts in the landscape, greenhouses, and nurseries. Home garden plants also can be very susceptible to twospotted spider mite damage.  Twospotted spider mites are most active in hot dry weather.  Begin monitoring susceptible plants in late May as weather becomes warmer. Look on the undersides of leaves for webbing, eggs, shed skins, and mites. An efficient way to monitor is to beat plant foliage on a paper plate or other white surface.  Mite will be easily distinguished from dirt and other debris because they will be moving.  Check plants weekly as populations can outbreak very quickly.

Decision making:

Intervention/Control

Typically twospotted spider mites overwinter in the soil as adults that reemerge in spring.  However, with mild winter weather, they may continue to feed and lay eggs at a reduced development rate.  Twospotted spider mites will also overwinter and feed in cold frames and unheated greenhouses.  Thus, nurseries may incur rapid damage in spring when plants are removed from these houses and placed outside because populations have been building all winter.  These residual populations can be reduced by monitoring populations in cold frames and preventing the temperatures from increasing on sunny days.

Twospotted spider mites feed on many weeds and other wild plants such as blackberries.  Therefore sanitation of nurseries and landscapes to remove these alternative hosts could reduce infestation of ornamental plants nearby.

Control of spider mites depends heavily upon an understanding of the biology of the mites. These mites are usually found on the underside of leaves. Thorough application of pesticides to the underside of the plant foliage is essential for good control. In hot weather, another application may be suggested 7 to 10 days later, to kill mites that were in the egg and resting stages during the first application. In hot weather, plants should be examined regularly for reinfestation or for the offspring of mites missed on the first application.

Newer miticides that have longer residuals and target all mite life stages are good alternatives to products that rely on contact to achieve control.  These products are also safer for beneficial insects than broad spectrum insecticides. This can prevent resurgence of mite populations or secondary pest outbreaks that occur when pests that were not killed by insecticides are released from predation because all the natural enemies were killed. 

See a Texas publication about using high pressure water spray.

Table 1. Some of the insecticides labeled for use on mites in ornamental systems
that are considered compatible with beneficial insects.

See NC Pesticide Manual for more choices.
*Suitable for home use.

Other Resources

• Back to Insect Notes
• Horticulture Information Leaflets(HILs)
• Plant Disease Notes
• North Carolina Agricultural Chemicals Manual
• North Carolina Cooperative Extension Service

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

ENT/ort-25
April 1994 (Revised) May 1997. (Revised) June 2009.

Web page last reviewed January, 2010 by the webperson.