Imported Willow Leaf Beetle (Plagiodera versicolora)

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- Imported from Europe in 1915, this leaf beetle is widely distributed in the Eastern United States and Southern Canada and has been sporadically reported throughout North America. In Europe, this insect is especially important in young plantations where impact can be severe. Beetle populations in North America have been kept at low levels by an imported pupal parasite. This insect is potentially more important than the cottonwood leaf beetle because of its ability to defoliate large trees as well as saplings and Populus species with leaf pubescence.

Look For: Signs of feeding defoliation -- skeletonizing or small holes being cut through the leaf; blackened shoots containing skeletonized small leaves. Heavily infested trees may turn brown to brown-black as early as mid-June. Oval, metallic blue to greenish-blue beetles, less than one-fifth inch long, often in clusters feeding on poplar or willow leaves beginning in late April and May and continuing through the growing season. Later in the spring, nearly jet-black larvae with rows of protuberances running both across and longitudinally on their bodies, about one-fifth inch long when fully grown. These larvae also feed on poplar and willow leaves.

Leaves skeletonized by imported willow leaf beetles.

Biology- Two or three generations are found in New England; five generations are found in Virginia and North Carolina. Adult females lay irregular masses of eggs on leaves. The larvae feed gregariously, skeletonizing the leaves. Adults overwinter under bark or in grass or debris around and near the bases of trees.

Control: Low winter temperatures and an imported pupal parasite have held down population levels of this beetle in most areas of the United States, indicating that direct control measures may not be needed. During severe infestations, this beetle can be controlled by following the recommendations given for the cottonwood leaf beetle.

Adult willow leaf beetles congregating on leaves.