The elm leaf beetle, Pyrrhalta luteola will feed on all species of native and introduced elm and zelkova. All stages of the elm leaf beetle develop on or near the elm tree. Adult beetles are about 1/4 inch long and range in color from yellow to olive green with a black stripe along each side of the back. These stripes may not be distinct. Adults feed on elm leaves. Eggs are laid in clusters of 5-25, usually on the undersides of leaves. They are yellow to white and spindle shaped. The immature beetles, called larvae, are six legged, wingless and are about ½ inch when mature. The color varies from black to dull yellow with a series of black spots or longitudinal stripes along the back. They usually feed on the lower leaf surface. Transformation of larvae into adults occurs in a stage called the pupa, which can be found in crotches of lower limbs, bark crevices, and in the soil and debris beneath the tree. Pupae are about 3 inches long, orange to yellow and do not move.
Damage results from the feeding activities of adult and immature beetles on elm leaves. Heavy feeding causes leaves to turn brown, wither and drop prematurely. Severe infestations can cause trees to develop an unsightly, scorched appearance. Damaged trees may put out a second flush of leaves that are also attacked. Repeated defoliation may reduce tree vigor and increase susceptibility to more serious pests such as the smaller European elm bark beetle. It is responsible for spreading the Dutch elm disease fungus.
Control of this beetle will be most effective when community members cooperate in the use and timing of control measures. This will help reduce the movement of beetles from untreated trees back to treated ones. Sprays should be timed to kill small larvae following egg hatch (mid-late May and July-August in Maryland). M-Trak® is a biological insecticide (Bacillus thuringiensis var. Tenebrionis) that is effective against the elm leaf beetle larvae. It is the safest material available to control this beetle. Labeled conventional insecticides may be used to control both adults and larvae. Read the label care for rates, timing of sprays, and for safety precautions.
Adult beetles may be excluded from the home by screening, caulking and weather stripping. Beetles that gain entry may be swept or vacuumed and disposed of.