Forest Tent Caterpillar (Malacosoma disstria)

From: Ostry, Michael E.; Wilson, Louis F.; McNabb, Harold S., Jr.; Moore, Lincoln M. 1988. A guide to insect, disease, and animal pests of poplars. Agric. Handb. 677. Washington, DC: U.S. Department of Agriculture. 118 p.

Importance- The larvae of this common insect defoliate all species of Populus. Outbreaks occur periodically and cause widespread defoliation.

Look For: Partly or completely defoliated trees Bluish larvae 1½ to 2 inches long with white keyhole-like markings up and down the back. Tan brown hairs adorn the sides. Yellowish cocoons with black pupae on the leaves or shoots. Black-gray egg masses around shoots in fall and winter.

Cluster of forest tent caterpillar Photo by Steven Katovich, USDA Forest Service

Biology-  There is one generation a year. Larvae emerge and feed 5 to 6 weeks on the foliage. At first the larvae are highly gregarious, but later they split into small groups. Cocoons are formed in August. Moths emerge about 10 days later, and the females lay eggs that overwinter in a mass in a band around the small shoots.

Monitoring- Check trees for defoliation or larvae in early summer; consider treatment if more than 60 percent of the leaves are injured or trees have been heavily defoliated 2 years in a row. Survey for egg masses in winter or fall after leaves have dropped. If there is more than one egg mass per branch, consider control the following year.

Control:

• It is usually impractical to control this insect in extremely large areas. In small stands, apply Bt (Bacillus thuringiensis) or a recommended chemical insecticide when the insects are in the early larval stages.