Adult beetles are about 1/4 inch long, overall yellow to brownish-green in body color, and marked with black spots on the head and thorax, and broad black stripes following the outer wing cover (elytra) margins. Larvae grow to about ½ inch and are yellowish with black spots and broad stripes along the sides. Pupae are 1/4 inch long and are bright orange-yellow with scattered black bristles.
Adult beetles spend the winter in protected sites, occasionally in homes. Beetles fly to elm trees in the spring, feed on newly-emerged foliage and deposit clusters of 5 to 25 lemon-shaped yellow eggs in two or three rows on the underside of leaves. In about 7 days, small black larvae hatch and feed on the underside of leaves. Larvae develop through several stages (instars) for about 21 days. Mature larvae crawl down the tree trunk and pupate in the soil at the base of the tree. Adult beetles emerge from pupae in about 14 days. Three or more generations can occur per year.
Larvae and adult stages are harmless to man and animals, but feed on leaves of elm trees causing unsightly damage and premature defoliation. Larvae skeletonize foliage by removing the parts of the leaves between the leaf veins, leaving the upper leaf surface intact. Injured portions of leaves soon turn rusty, reddish-brown, and dry skeletonized leaves fall to the ground. Adults eat roughly circular holes in leaves.
Healthy elms can tolerate substantial defoliation. Protect trunks and roots from injury. Check for dead or dying branches and properly prune these out during late fall and winter. Avoid pruning elms during spring and summer; fresh pruning wounds attract feeding during these seasons. Where elm leaf beetle is a problem, use a combination of methods because no single method makes the pest populations less susceptible to that treatment. Good cultural care of trees is an essential component of integrated pest management.