Elm Leaf Beetle

Elm Leaf Beetle,Cotinus nitida (Linnaeus) a group containing dung beetles. This beetle is found in the eastern region of the united states NY, NJ, Connecticut.

Adults are olive-green beetles with black, longitudinal stripes along the margin and center of the back. Females lay their yellowish to gray eggs in double rows of about 5 to 25 on the underside of leaves. Larvae are black when newly hatched. After feeding, they become a dull yellow or green with rows of tiny dark tubercles (projections).

Larvae develop through three stages called instars. Third-instar larvae have dense rows of dark tubercles that resemble two black stripes down their sides, making them easy to distinguish from first- and second-instar larvae. Mature third instars are up to 1/3 inch long. Pupae are orange to bright yellow.

Elm leaf beetles feed on elm tree leaves. During heavy infestations, leaf chewing affects the appearance of elm trees. Spray with insecticides to control elm leaf beetles.Trunk banding or systemic insecticides are alternative means to control elm leaf beetles on trees.Elm leaf beetles may be serious nuisance problems when they enter homes to overwinter. They may become active during warm periods until they move outdoors or die.Elm leaf beetles do not feed or reproduce when indoors.

Elm leaf beetles can be serious pests of elm throughout Colorado. The insects feed on elm leaves and cause them to dry up and die. Heavily infested leaves die and give trees an unsightly, general brown color. Repeated injuries also weaken trees and make them prone to branch dieback and wind injury. Elm leaf beetles favor Siberian elms, but all elm species may be damaged during beetle outbreaks.

Life Cycle: This species overwinters as adults in houses, sheds, and in protected places outdoors such as under loose bark of trees or house shingles. In late spring adults leave their overwintering sites, fly to nearby elms, mate, and begin laying eggs. Adults eat small, rough circular holes into the expanding leaves.Eggs are laid on end in groups of 5-25 on the underside of host plant foliage. Each female may lay 400-800 eggs over her life span.

Larvae feed on the lower leaf surface. Larvae feed for 3 weeks resulting in skeletonization of the foliage. The upper leaf surface and veins are left intact.At the end of the feeding period larvae migrate to lower parts of elm trees in cracks, crevices, or crotches on the trunk and larger limbs. It is in these protected places that pupation occurs, and adults emerge 7-14 days later during mid- to late summer. There is one complete generation and a partial second generation produced each year in Pennsylvania.

Eggs are orange-yellow and spindleshaped. Larvae are small, black, and grublike. At maturity larvae are approximately 13 mm long, dull yellow, and with what appears to be two black stripes down the back. Adults are about 6 mm long, yellowish to olive green with a black stripe along the outer edge of each front wing”

Damage: Injury caused by this pest may result in partial or complete defoliation of trees. Heavily infested foliage will turn brown and often drops prematurely. In some cases by mid-summer an entire tree may be defoliated. The majority of damage is caused by larvae feeding on the lower leaf surface. Trees that lose foliage as a result of heavy damage by this pest commonly produce a new flush of growth that may be consumed by the remaining insects found on the host tree. Hibernating adults in homes do not cause structural damage but may be a nuisance.

Feeding damage by this key pest seldom kills an elm tree. Severe defoliation may weaken a tree, making it more susceptible to attack by other insects and diseases such as Dutch elm disease. This pest does not carry Dutch elm disease, but the smaller European elm bark beetle, Scolytus multistriatus , and the native elm bark beetle, Hylurgopinus rufipes , that attack weakened trees, do. Even without secondary attack by other insects and diseases, repeated attacks by the elm leaf beetle may eventually weaken trees to the point of death.

Control: Elm leaf beetle, Xanthogaleruca (=Pyrrhalta) luteola, is one of the most important insects damaging urban forests in the United States and is the major pest of elm trees in California.Adults are olive-green beetles with black, longitudinal stripes along the margin and center of the back. Females lay their yellowish to gray eggs in double rows of about 5 to 25 on the underside of leaves. Larvae are black when newly hatched. After feeding, they become a dull yellow or green with rows of tiny dark tubercles (projections). Larvae develop through three stages called instars. Third-instar larvae have dense rows of dark tubercles that resemble two black stripes down their sides, making them easy to distinguish from first- and second-instar larvae. Mature third instars are up to 1/3 inch long. Pupae are orange to bright yellow. Elm leaf beetle has at least one generation a year in northern California and two to three generations in central and southern California.

Several introduced and native natural enemies kill elm leaf beetles, but generally do not provide adequate control by themselves. The most important parasite in California is a small, black tachinid fly (Erynniopsis antennata) that emerges from mature beetle larvae. Its black to reddish, cylinder- or teardrop-shaped pupae occur during spring and summer at the base of trees among the yellowish beetle pupae. Erynniopsis antennata overwinters in adult beetles, emerging as adults in spring, although this is not readily observed. Unfortunately, the effectiveness of E. antennata is limited by Baryscapus (=Tetrastichus) erynniae, a secondary parasite (hyperparasitoid) that kills the beneficial parasite.

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