Elm Leaf Beetle

The common name no doubt reflects the fact that this species is a major pest of elm trees. Elm leaf beetles are primarily a nuisance pest because they enter structures in the autumn to overwinter. They were introduced from Europe and first reported occurring near Baltimore, Maryland, in 1834. They are found throughout the United States wherever elms grow.

Recognition

Adults are about 3/16-1/4 inch long; oval, are soft-bodied. Color at first light yellow with a black stripe along each eltral outer margin, in time yellow dulls to olive green and black stripes become less distinct; pornotum white with a black mark on each side and a narrow black central mark; head with a small black mark on top between eyes. Eyes not notched. Antenna slightly less than half as long as body. Pronotum with a lateral margin. Tarsi appearing four-segmneted, third segment bilobed, fourth very small, concealed between lobes of third.

Mature larva are up to 1/2 inch long; somewhat hairy. Color of early instars changing from blackish to dull yellow with black head, legs, and hairs, and with two black lateral stripes; later instars dull yellow and are speckled, with two black lateral stripes less distinct.

Habits

In southern states, the females begin egg laying in late April, but they do not start until late May or early June in the northern states. Outside, the fecal material from both the adults and larvae can spot car finishes, especially on hot summer days.

Both larvae and adults feed on the leaves of elm trees. They prefer the Siberian elm and the hybrid urban elm as food over other elm species; another preferred food is Japanese zelkova. The larvae eat only the undersurface of the leaves, leaving the veins and upper surface, which then dry, resulting in leaf skeletons. Leaves eventually turn brown as if scorched by fire and drop off the tree.