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FutureStarrA Wild Leek Flower
Elm leaf beetles (Xanthogaleruca luteola) are common insects that chew leaves of elm trees (Figure 1). The dark grub-like larvae chew on the underside of leaves but avoid the larger leaf veins, producing a type of injury pattern known as skeletonizing (Figure 2). Leaves damaged by elm leaf beetle larvae look lacy, turn brown and may prematurely drop from the trees (Figure 3). Adult beetles chew irregularly round holes in the center of leaves. Siberian and English elms are particularly favored by this insect.
Elm leaf beetles also can be important as a nuisance pest in homes, because they often enter buildings in autumn when seeking winter shelter. Beetles that do work their way behind walls and other areas of buildings may then be found indoors until spring, becoming most active during warm periods. Fortunately elm leaf beetles are strictly a nuisance invader type of insect that does not feed on nor damage anything within a home, although their very presence in a home is a common cause of concern.Beginning around 2006 an additional beetle arrived in Colorado that feeds on elm, the European elm flea weevil (Orchestes alni). European elm flea weevil produces some leaf injuries, such as shotholes in leaves, which are similar to those produced by adult elm leaf beetles. This new insect of elms is occurs throughout the state and is discussed at the end of this sheet.
Elm leaf beetles overwinter in the adult (beetle) stage. In late summer and early autumn they seek out protected sites such as woodpiles, loose mulch, and piled eaves to shelter through winter. Often cracks and other openings that allow them to get behind building walls serve as winter shelters. During this period the beetles are in a semi-dormant state (diapause) and are a khaki-green color (Figure 4). While in this dormant state they do not feed nor reproduce but may become active during warm days in late winter and spring.Few natural enemies feed on elm leaf beetles. Insect predators, such as predaceous stink bugs and plant bugs, may feed on various stages of the elm leaf beetle. There are small parasitic wasps that attack larvae and pupae, although incidence of these appears to be very low in Colorado. Some pupae may be killed by Beauveria bassiana, a fungus that produces disease in many insects, but infections with this disease require conditions of high humidity and outbreaks are uncommon in arid sites. (Source: extension.colostate.edu)