by Lee Townsend, Extension Entomologist
University of Kentucky College of Agriculture
Adult elm beetles are about 1/4 inch long and yellow to olive green with a dark stripe down each side of their wing covers. There are usually four dark spots on the pronotum (segment right behind the head).
The eggs are orange, spindle-shaped and the larvae are wormlike, black or black and yellow and up to 1/2 inch long. The pupae are orange-yellow with black bristles.
Adult elm leaf beetles overwinter in protected locations, often in houses or other structures. They emerge in the spring and move to elm trees where they lay their eggs in groups of 5 to 25 on the underside of leaves. The larvae skeletonize the leaves making them appear netlike. Elm leaf beetle larvae often move to the base of the tree in large numbers to pupate. There are two complete generations per year.
Elm leaf beetle adults move into buildings in the fall to seek hibernation sites. They do no damage but cause great consternation because of their presence in such large numbers.
The most effective control of elm leaf beetles is accomplished by controlling the larvae or adults while they are still on the tree. They can be controlled using sprays of insecticidal soap, light horticultural oils, carbaryl (Sevin) or Orthene (acephate). Treat when leaves are first fully expanded in the spring and again in July.
Adult beetles may be prevented from entering homes and structures using barrier treatments such as those used to prevent entry of boxelder bugs. Elm leaf beetles that successfully gain entry into the home can be eliminated by vacuuming them up from under carpets or other harborage areas or by using short residual contact insecticides such as pyrethrins to kill them.
CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.
Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!