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Oak Pests - A Guide to Major Insects, Diseases, Air Pollution and Chemical Injury

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Lymantria dispar

Importance. -- The gypsy moth, which came from France, has long been considered one of the most important pests of red and white oaks in the Northeast. It has spread southward to North Carolina and appears to be moving in on southern hardwoods. It causes widespread defoliation resulting in reduced growth, loss of vigor, mortality, and reduces aesthetic, recreational and wildlife values.

Identifying the Insect (figure 7a). -- 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. Larvae are about 1.6 to 2.4 inches (40 to 60 mm) long. Adult females are whitish and males are dark brown.

Identifying the Injury (figure 7b). -- Young larvae chew small holes in leaves. Older larvae feed on leaf edges, consuming entire leaves except for the larger veins and the midrib. The entire tree may be defoliated.

Biology. -- Larvae emerge in May from overwintering eggs and feed until mid-June or early July. Pupation occurs in sheltered places and lasts 2 weeks. Adults emerge in July and August. Females deposit masses of 100 to 800 eggs covered with buff-colored hairs on trunks and other sites.

Control. -- Natural controls including introduced insect parasites and predators, virus disease, and adverse weather conditions help control the gypsy moth. Chemical and microbial insecticides are used extensively.

Figure 7a
Figure 7b

Figure 7. -- (a) Gypsy moth larva; (b) defoliation by gypsy moth.

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