Elm Leaf Beetle (Pyrrhalta luteola)
Anonymous. 1989. Insects and Diseases of Trees in the South. USDA Forest Service. Protrotection Report R8-PR16. 98 pp.
The elm leaf beetle attacks all species of elm. However, in most of its range, the beetle prefers the Siberian elm. When defoliation is severe for several consecutive years, limbs and sometimes the tree may be killed. The beetles may become a nuisance in the fall when they move into homes searching for overwintering sites. The adults may be a problem in the spring when they congregate in windows as temperatures increase.
Identifying the Insect
The larvae are green to yellow, with a black head and two black stripes on the back. Pupae are about 1/4 inch (6 mm) long and bright orange-yellow. The adults are approximately 1/4 inch (6 mm) long and yellowish to green with a black stripe on each wing margin.
Identifying the Injury
Adults chew holes in the leaves, particularly on new growth. The larvae feed on the under surfaces of leaves, leaving upper surfaces and the veins intact. Leaves shrivel and turn brown when damage is severe.
In the spring the adults fly to elms and eat small holes in the newly developing leaves. Eggs are laid in a cluster on the undersides of leaves. The eggs hatch and the larvae feed for 2 to 4 weeks. The larvae crawl to sheltered places on the tree or ground to pupate. In one to two weeks new adults emerge and again feed and lay eggs. There are two to four generations per year, depending on the geographical location.
No chemical controls are recommended in forest stands. Homeowners may use recommended insecticides to protect valuable shade trees. Sprays should be directed at the undersides of the leaves, beginning in the early spring.