Large Aspen Tortix (Choristoneura conflictana)

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 insect are voracious feeders that destroy the buds and leaves of Populus in the Northern United States and Canada. Outbreaks frequently last for several years and then disappear. Heavily and repeatedly defoliated trees or trees with buds removed lose vigor and may die.

Look For: Tightly rolled leaves. Greenish larvae or brown pupae on the rolled-up leaves in early summer.

Rolled Leaf Photo by Steven Katovich, USDA Forest Service

Biology- In mid-June, female moths lay their eggs in large clusters on the upper surface of leaves. The young larvae emerge in about 10 days and feed gregariously inside leaf shelters. The larvae overwinter in protected places. In spring, they emerge, penetrate the opening buds, and feed. Later they roll the leaves and feed inside them until pupation in July.

Monitoring- Check trees for injured tips or rolled leaves in the spring and summer. Consider control only if trees are more than 90 percent defoliated of if heavy defoliation occurs 2 or more years in a row. Natural factors usually keep the populations in check after 2 or 3 years.

Large aspen tortrix larva Photo by Jeffrey J. Witcosky, USDA Forest Service

Control:

• It is usually impractical to control the insect in extremenly large areas. In small stands, apply Bt (Bacillus thuringiensis) when the insects are in the early larval stages.
• Apply a registered contact insecticide to the trees after larvae become active in the spring or when larvae migrate to overwintering sites in the fall.