Strawberry Rootworm

Paria fragariae

Biology
Adult strawberry rootworms are brown to black, shiny, oval-shaped beetles with four blotches on the shell-like wing covers. Adult beetles overwinter in mulch and soil crevices and become active in May and June. They eat small holes in leaves, and females lay eggs on older leaves near the soil surface. Larvae burrow into the ground to feed on strawberry roots during the summer. New adults begin emerging in mid-summer, and these beetles feed on strawberry foliage through early fall.

Damage
Although the larvae of the strawberry rootworm, Paria fragariae, feed on the roots of strawberry (as the insect's common name implies), leaf-feeding by adult beetles is more damaging to strawberry production. When adults become numerous during mid-summer, strawberries may be riddled with holes.

Control
Adults feed primarily at night, and scouting for their presence is best done by using a flashlight to examine plants after dark. Populations of 10 to 20 beetles per square foot are considered high. Although the Illinois Commercial Small Fruit and Grape Spray Guide contains no recommendations specifically for the control of adult strawberry rootworms, postharvest sprays of insecticides registered for other pests (in 1996, Guthion, Sevin, or Thiodan) also control this insect. Unnecessary sprays should be avoided, however, so that predaceous mites are not killed, leading to outbreaks of spider mite populations.

Although strawberry rootworms occur in many fields, these pests do not damage berries directly and often do not reach high densities. Consequently, controlling them is often unnecessary. Insecticide applications for the control of foliage-feeding pests can and should be based on scouting results, not preventive spray programs.