Description: Young larvae are dark-colored, hairy grubs. Older larvae are yellow with two long, dark stripes. Adult beetles have green and yellow stripes and are about 1/3-inch long.
Life Cycle: There are typically two generations of elm leaf beetles each year. They overwinter as adults and emerge from their protective shelters in early spring. As elm trees develop leaves the beetles move in and females begin laying eggs. Larvae hatch and spread throughout the tree to feed. Larvae reach maturity within four weeks and seek shelter to pupate. They may drop to the base of the tree or crawl within cracks of the bark to pupate. Adults emerge in about two weeks and relocate to the leaves to eat and mate giving rise to the second generation of larvae. This generation of adult beetles will wait to lay eggs until the spring.
Damage: Larvae cause most of the damage by skeletonizing leaves of elm trees, giving
preference to Siberian (Chinese) elms. Adult beetles chew holes through the leaves. Leaves that have been heavily damaged may turn brown and drop.
Control: For healthy trees, at this point in the season, elm leaf beetles and larvae tend not to cause significant damage so spraying is not recommended. If the larvae are active, they can be controlled with several insecticides. If they have already dropped to pupate spraying will be ineffective.
Larvae and adult sprays include: acephate (Acephate, Orthene), spinosad (Natural Guard
Spinosad, Conserve, Captain Jack’s Dead Bug Brew, Monterey Garden Insect Spray), lambda cyhalothrin (Scimitar, Spectracide Triazicide).
Cynthia Domenghini, Extension Agent
