Importance. -- Outbreaks occur periodically on oaks and other hardwoods over wide areas of the eastern half of North America. Growth loss and dieback occur, but trees are seldom killed unless they sustain 3 or more successive years of defoliation.

Identifying the Insect (figure 6a). -- Caterpillars have pale bluish lines along the sides of a brownish body; a row of keyhole-shaped white spots down the middle of the black back; sparsely covered with whitish hairs; and reach 2 inches (50 mm) at maturity. Adult moths are buff brown with darker, oblique bands. Egg masses of 100 to 350 eggs encircle the twigs and are covered with frothy, dark brown cement.

Identifying the Injury (figure 6b). -- The first noticeable signs of attack are sparse crowns and falling frass. Caterpillars often cluster on the lower trunks of infested trees. Trees or even stands may be completely defoliated during spring.

Biology. -- Eggs hatch in early spring. Caterpillars feed for 4 to 6 weeks on the opening buds, foliage, and flowers. Despite its name, this species does not form tents. Pupation occurs in yellowish cocoons and lasts 10 to 14 days. Moths emerge from late May to July and deposit their eggs, which overwinter. There is one generation per year.

Control. -- Natural controls include insect parasites of the pest's eggs, larvae, and pupae. Predators, virus and fungus diseases as well as high and low temperatures also kill forest tent caterpillars. Several chemicals and a microbial insecticide are registered for control.

Figure 6. -- (a) Forest tent caterpillar larvae; (b) defoliation by forest tent caterpillar.