Imported Willow Leaf Beetle Adult, larva and damage

Scientific Name: Coleoptera: Chrysomelidae, Plagiodera versicolora (Laicharting) 

Plants Attacked

Most willows (primarily on black and white willow; feeds but not severely on weeping willow). 

Description of Damage

The larvae skeletonize the underside of the leaves in feeding. The adults chew holes in the leaves, but the total area consumed is less than larvae. Trees can be turned completely brown from severe populations. Damaging stages - larvae primarily and adults. 

Identification

Adults are metallic-blue about 1/8" long, the eggs are yellow. Larvae are cream-colored when they molt but darken gradually to black. The body of the larvae bears many black and brown markings and is about 3/16" long when full grown. Eggs are yellow, spindle-shaped and laid on end in clusters on the undersides of the leaves.

Life History

The hibernating adult begins to emerge in the spring when foliage appears. These adults feed on the new leaves, cutting holes in them. The eggs are laid for the first generation and they hatch in about a week. In less than a month, usually the adults emerge from pupae which have been formed by larvae on the leaves. Adults of the 2nd generation develop in early July and a 3rd in early August. These adults feed heavily for a number of days and by the last of August, practically all have entered hibernation. Only a few of this generation mate and deposit eggs that develop into a partial 4th generation. Three and sometimes a partial fourth generation per year. Overwintering stages - adults, under bark or other shelter. 

Control

Control of willow leaf beetle is simply a matter of applying a residual spray when larvae are first noticed hatching from egg masses. In areas where willow leaf beetle is established, it will be necessary to treat 2 or 3 times during the season for 2nd and 3rd generations. Plants should be checked periodically for the presence of egg masses and newly emerged larvae. 

Information provided by the Virginia State University Extension Service