Forest Pests: Insects, Diseases & Other Damage Agents

The forest tent caterpillar is a native insect that occurs throughout most of the United States and Canada. This caterpillar feeds on a wide variety of hardwoods. In the North and West, trembling aspen is preferred. Forest, orchard, and ornamental trees are also acceptable, and several extensive outbreaks of the insect have occurred in the past.

Eggs are laid in masses containing 100 to 350 eggs. The mass is a cylindrical band, ringlike in shape and 25 to 37 mm (1 to 1.5 in.) wide, that encircle the twig (fig. 20). The ends of the mass are square, and the whole mass is coated with a dark-whole mass is coated with a dark colored, glue-like substance. Winter is spent in the egg stage, and hatching occurs in the spring about the time the tree buds begin to swell.

Young larvae feed on the expanding buds; the older ones eat the foliage. Young larvae from one egg mass feed together as a group on a leaf or leaf cluster. As the larvae grow and mature, the group breaks up and each larva feeds alone on the foliage. Full-grown larvae are about 50mm (2 in.) long with a light bluish-black head and a few scattered white hairs. The back of the body is marked lengthwise with a row of whitish-yellow, keyhole-shaped spots. The remainder of the body is various shades of gray (fig. 21).

Larvae lay down strands of silk as they move about. They also form silk mats on the trunks and branches on which they collect in-groups to rest between feedings. Contrary to the common name, a tent is not constructed by the larvae. As they approach maturity, they wander about individually in search of food or places to pupate.

Pupation occurs in pale-yellow cocoons about 25 mm (1 in.) long that are spun in folded leaves, bark crevices, and other protected sites (fig. 22). Depending on the geographic location, the appearance of adults occurs from late May in the South to early July in the North. The stout-bodied, light buff-brown adults have a wingspread of 25 to 37 mm (1 to 1.5 in.) (fig. 23).