Imported Willow Leaf Beetle
Contact: Eric Day, Manager, Insect Identification Laboratory
August 1996
Imported Willow Leaf Beetle
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.
Imported Willow Leaf Beetle adult, larvae and damage.
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.