Malacosoma disstria

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Superorder	Holometabola
Order	Lepidoptera
Superfamily	Lasiocampoidea
Family	Lasiocampidae
Subfamily	Malacosominae
Tribe	Malacosomini
Genus	Malacosoma

Scientific Name

Malacosoma disstria

Common Name

forest tent caterpillar

Complied by:Joseph LaForest, University of Georgia

Overview

Forest tent caterpillar, Malacosoma disstria, occurs throughout Canada and the United States and is a generalist defoliator that feeds on a variety of hardwood trees. In the north and west of the United States (and southern Canada), trembling aspen (Populus tremuloides) is preferred. In the southern United States, various gums (Nyssa spp. and Liquidambar styraciflua L.) and oaks (Quercus) are the common hosts. However, during outbreaks, larvae will feed on a wide variety of hardwood species. Winter is passed as eggs, which hatch in spring. Larvae begin feeding on buds and expanding leaves. Older larvae feed on mature leaves. Young larvae feed in groups, but older larvae are dispersed. Larvae lay silk trails, which they follow, but they do not form a silken tent. Rather, they make silk mats on which larvae rest. Mature larvae wander and pupate inside a yellowish-white cocoon fixed to the host tree or other objects. Adults emerge in midsummer (north) or spring (south) and lay their eggs in clusters that encircle twigs of the host tree. Eggs are cemented together and covered with dark colored material called spumaline. There is one generation per year. A number of very large outbreaks, covering thousands of square miles and lasting for several years, have occurred in North America. Tree mortality is generally low, but loss of growth can be considerable (>70%) due to effects of defoliation. In the southern United States, in bottomlands, gum trees may die from defoliation. In the northeastern United States, defoliation of sugar maple stands lowers maple syrup yields and quality.

Identifying the Insect

The larvae have pale bluish lines along the sides of a brownish body, and a row of keyholeshaped white spots down the middle of the back. They are sparsely covered with whitish hairs, and reach 2 inches (50 mm) at maturity. Adult moths are buff-brown, with darker oblique bands on the wings. Egg masses of 100 to 350 eggs encircle the twigs and are covered with frothy, dark brown cement.

Identifying the Injury

The first noticeable signs of attack are sparse crowns and falling frass. Caterpillars often cluster on the lower trunks of infested trees. Single trees or complete stands may be completely defoliated during the spring.

Biology

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. 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.

Caterpillars feed for 4 to 6 weeks on the opening buds, foliage, and flowers. 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.

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. Pupation lasts 10 to 14 days. 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.).

Moths emerge from late May to July, mate, and deposit their eggs. There is one generation per year.

Control

Natural control agents include insect parasites of eggs, larvae, and pupae. Predators and viruses and fungus diseases, as well as high and low temperatures, also kill forest tent caterpillars. Starvation is common when populations exceed the food supply. Several chemicals and a microbial insecticide are registered for control.

Gallery

References

• Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16. 98 pp. Taken from http://fhpr8.srs.fs.fed.us/forstpst.html
• Talerico, R. L., 1978. Major hardwood defoliators of the Eastern United States. U.S. Dep. Agric., Home and Garden Bull. 224.