Forest Health Protection, Southern Region

Importance. - The gypsy moth, which came from France, is considered one of the most important pests of red and white oaks in the Northeast. It has spread southward into Virginia and is continuing to move south. Favored host species are oak, apple, alder, basswood, birch, poplar, sweetgum, willow, and hawthorn. Less favored are hickory, maple, cherry, cottonwood, elm, blackgum, larch, sassafras, and hornbean. Some mortality even occurs in white pine. It causes widespread defoliation, resulting in reduced growth, loss of vigor, mortality, and reduces aesthetic, recreational, and wildlife values. Gypsy moth larvae can be a serious nuisance in urban and recreation areas.

Identifying the Insect. - Older larvae are brownish-gray, with tufts of hair on each segment and a double row of five pairs of blue spots, followed by six pairs of red spots, on the back. Mature larvae are from 1 1/2 to 2 1/2inches (40 to 60 mm) long. Adult male moths are dark brown, with wavy dark bands across the forewings. Females are white and cannot fly.

Identifying the Injury. - Young larvae chew small holes in leaves. Older larvae feed on leaf edges, consuming entire leaves except for the larger veins and the midribs. The entire tree is often defoliated.

Biology. - Larvae emerge in late April or early May from overwintering eggs and feed through June and into early July. Pupation occurs in sheltered places and lasts 2 weeks. Adults emerge in July and August. Females deposit egg masses (100 to 800 eggs) covered with buff-colored hairs, under rocks and on tree trunks, limbs, houses, picnic tables, trailers, campers, mobile homes, cars, and other sheltered places.

Control. - Natural controls, including introduced insect parasites and predators, virus diseases, and adverse weather conditions, help control the gypsy moth. Chemical and microbial insecticides have been used, primarily in urban and recreation areas, to prevent defoliation and the nuisance effects of the pest.