Importance. - Outbreaks of the locust leafminer are generally more spectacular than destructive. In combination with other stress factors, infestations can contribute to growth loss and even mortality. The major hosts are black locust and honeylocust. Other tree species (apple, beech, birch, cherry, elm, oak, and hawthorn) are occasionally attacked.
Identifying the Insect. - The adult is a small, elongated, flattish beetle, about 1/4 inch (5 to 6 mm) in length. The head is black, and the thorax and most of the wing covers are orange. The full-grown larvae are yellowish, flat, and slightly larger than adults.
Identifying the Injury. - Adults skeletonize and eat holes in the leaves, whereas larvae mine the leaves (the latter damage is more destructive). Under outbreak conditions, whole hillsides turn gray or brown, often suggesting fall color change.
(Click for detail. JPG 48K).
Biology. - Adults overwinter in bark crevices or in leaf litter and emerge about the time leaves begin to unfold in the spring. Eggs are deposited on the undersides of locust leaflets. They overlap like shingles in groups of three to five and are cemented together by excrement. Upon hatching, the larvae first feed collectively in a common, blisterlike mine. Then, the larvae disperse, excavating their own individual mines. Pupation occurs within the translucent blisters in July. There are two generations annually.
Control. - Control of the locust leafminer is generally not necessary. When aesthetics are involved (such as in park, shade tree, or recreation situations), control might be justifiable.