Two-spotted Spider Mite

family: tetranychidae
species: tetranychus urticae
common names: two-spotted spider mite, strawberry spider mite (t. turkestani), pacific spider mite (t. pacificus)
antennae characters: none
specialties: vectors plant diseases
hosts: all plants, beans, cucurbits, strawberries, apples, beans
natural enemies: predaceous mites, phytoseiulus persimilis, phytoseiulus longipes, amblyseius californicus, amblyseius fallacis
cultural control methods: avoid water stress to plants
pesticides used: oil based miticides
notes: most important family in acari, they feed on leaves by removing plant sap and have rapid reproduction

Agriculture and Agri-Food Canada Insect Identification Sheet No. 47 March 1981

Two-spotted Spider Mite

Tetranychus urticae (Koch)

The two-spotted spider mite is found across Canada. A serious greenhouse pest, it also attacks strawberries, brambles, fruit trees and vegetable crops.

Injury:

Plant injury is caused by the mites feeding on host plant juices. They feed primarily on the lower surfaces of leaves, usually attacking the leaves in the center of larger plants first and then spreading outward. If infestation is light, the leaves become covered with pale blotches and webbing. Heavy infestation causes leaves to bronze and drop off, fruit to be reduced in size and quality, and growth to be retarded. Webbing may cover the entire plant, which may ultimately die.

Life History:

two-spotted spider mites overwinter as adult females in bark crevasses of trees or under protective ground litter. Overwintering females are bright orange. Early in the spring they become active and lay their eggs. The straw-colored eggs are attached to the undersides of weed or tree leaves. Within 3 to 10 days (depending on the temperature) the six-legged larvae emerge. After passing through the eight-legged protonymph and dentonymph stages, adult mites appear. Summer forms are yellowish-brown or greenish, with typically a pair of dark spots of internal body content, which give the mites their common name. They are extremely small, with the adult female attaining a length of 0.3 to 0.4 mm and the male 0.3 mm. There may be many generations per year, with populations peaking in August or September.

Pest Management:

For information on control, contact your provincial Department of Agriculture. If chemical controls are necessary, summer sprays must be used, as dormant sprays are not effective against the overwintering adults.

THE FOLLOWING (UNTIL OTHERWISE NOTED) IS FROM: GERBER, H.S. 1983.
MAJOR INSECT AND ALLIED PESTS OF VEGETABLES IN BRITISH COLUMBIA.
MINISTRY OF AGRICULTURE AND FOOD.

Two-spotted Spider Mite, Tetranychus urticae Koch

Populations increase rapidly under hot, dry conditions. Damage to foliage is often mistaken for drought symptoms.

Vegetables Attacked:

Bean, cucurbits: cucumber, pumpkin, marrow, squash, melon

Injury:

Leaves, pods and other above ground parts are initially speckled; later they become bronzed or brown. Fine webbing is produced mainly on the lower surfaces of leaves.

Mite:

Adult females are pale yellow or green with a black spot on each side of the body. Males are smaller, indefinitely colored and less numerous. Immature stages are similar in general shape and color to the female, but are not so definitely marked. Eggs are round, translucent and scattered in the webbing. Overwintering females are orange.

Life History:

There are many generations each year; in hot weather a generation is completed in two weeks. Females overwinter in trash or in soil at the base of the host plant.

Control:

Plants should be inspected frequently in hot weather and, if the population of mites begins to increase, a control treatment should be applied immediately

Written under contract to the BC Ministry of Environment, Lands and Parks (now Ministry of Water, Land and Air Protection ) by: D.E. Henderson, E.S. Cropconsult Ltd., Vancouver, British Columbia in collaboration with D.A. Raworth, Research Station, Vancouver, British Columbia:

Adults of the two-spotted spider mite (Tetranychus urticae Koch) are barely visible without magnification. They are greenish yellow with two dark spots on their back. They feed by sucking plant sap from the undersides of leaves. Infested leaves develop a white speckling, which makes them appear dull and pale. In heavy infestations, leaves turn brown and fall off. Spider mites produce a silk webbing that covers the undersides of the leaves where they feed. Females spend the winter as red-orange adults on mature foliage, under trash, in leaf litter, or in the soil at the base of the plant. In the spring, they move to the new leaves to feed and lay eggs. Hot dry conditions encourage two-spotted spider mite populations to increase. Dust blowing from roadways near raspberry or strawberry plantings may have the same effect on the mite population.