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Elm Leaf Beetles

A serious pest of elm trees throughout Colorado, the elm leaf beetle overwinters in its adult form in cracks and crevices.  As spring leafs begin to emerge on elm trees, so do the adult elm leaf beetles that come to feed and start their egg laying process.  Eggs are football shaped and laid in clusters on the underside of leafs.  Upon hatching, the larvae feed on the underside of leafs, often causing the leaf to prematurely drop off.  Pupation occurs at or near the base of the trees with adults hatching in one to two weeks.  During growing seasons, adult elm leaf beetles are yellow with black stripping, whereas during the winter they turn dark in color and are more of khaki green.  Multiple generations may occur in a single season.  Overall damage typically results in leafs dying off, giving the tree a brown appearance; however, dieback and wind damage may also result from an elm leaf infestation due to weakening of the trees.  Elm leaf beetles are not responsible for the transmission on Dutch elm disease.  Treatment of infested trees through the use of insecticide applications may become necessary during infestations.  Applications are typically completed by pest control companies maintaining a license in ornamental pest control.  Natural predators of the elm leaf beetle also occur and include several predaceous insects.  In residential and structural areas, infestations occur when adults seek shelter in which to overwinter.  Active periods may be produced throughout the winter during spells of warmer weather.  Elm leaf beetles do not cause any interior damage and are considered as a nuisance pest.  Control of elm leaf beetles in structures is limited and exclusion is often the most effective method of control in these situations.  Elm leaf beetles do not reproduce inside, although periods of activity due to warm weather during the winter may give that appearance.