Now is the time to be on the lookout for the imported willow leaf beetle, Plagiodera versicolora, which is a pest of most willows and poplars. This beetle is pri-marily a problem in the northern third of Illinois. If left unchecked, this beetle can cause severe aesthetic damage to plants in landscapes.
Adults are black to greenish blue. The adults hide during the winter under loose bark or in protected places on the tree trunk. In spring, they feed on foliage and lay glossy, pale-yellow eggs on the underside of leaves. These eggs hatch into small (7 to 10 millimeters long) black larvae that feed on the leaf undersides. The larvae cause the most damage as they feed on the leaf tissue, leaving only the leaf veins. After feeding, the larvae enter into a pupal stage, which generally lasts 3 to 4 weeks. There may be two to three generations per year.
Treatment of imported willow leaf beetle is generally not required on plants in which the damage is not noticeable. However, large numbers of imported willow leaf beetle may warrant control. Pest-control materials that are recommended include Bacillus thuringiensis ‘tenebrionis,’ carbaryl (Sevin), and spinosad (Conserve). Bt ‘tenebrionis’ is only effective on the larval stage.