Forest Tent Caterpillar
Malacosoma disstria Hubner


Hanson, T., and E. B. Walker. [n.d.] Field guide to common insect pests of urban trees in the Northeast. Waterbury, VT: Department of Forests, Parks and Recreation. http://www.state.vt.us/anr/fpr/forestry/pubs/pest.html


Lepidoptera: Lasiocampidae

Hosts: Sugar maple, birch, oak, aspen and many other deciduous trees but never red maple.

Evidence: Shiny brown egg masses are present from July until early spring of the following year. They differ from those of eastern tent caterpillar in having square edges, and they completely encircle the twigs of host trees (a). Larvae, which are present in early spring, have distinctive keyhole-shaped white spots on the middle of the back of each segment (b). Defoliation of all except larger veins and petioles of the leaf occurs in May and June (c). The chunky chocolate-brown moths which appear in July do not have white bands on their wings. Their occurrence and density can be monitored with pheromone and light traps.

Life Cycle: Insects overwinter in masses of 150-200 eggs. Larvae emerge about the time leaves unfold in the spring and may feed at first on opening buds. Later they consume whole leaves. Unlike the eastern tent, forest tent caterpillars do not construct tents. They spin mats on which they rest and make pathways of silken threads to feeding sites (d). Pupation takes place in white, silken cocoons, often within rolled leaves. Adults emerge in July, mate, and lay eggs.

Management: Loss of woody growth and death of branches may result from heavy or repeated defoliation. Repeated defoliation, along with other stress factors, can kill trees or predispose them to disease or other pests. Bacillus thuringiensis and various chemical insecticides can be used to control larvae. The collapse of large outbreaks which occur periodically have been attributed to depletion of food supplies, unfavorable weather conditions, and natural enemies such as predators, parasites, and pathogens.

Similar Species: This species is closely related to the eastern tent caterpillar (C-1) and may also be associated with the gypsy moth (O-1).

a. Egg masses have square edges and completely encircle twigs on host trees.

b. Note the keyhole-shaped white spots on the back

c. Defoliation tends to be fairly complete with all except major veins and petioles consumed.

d. Forest tent caterpillars cluster in groups, but do not form tents.

Photo Credits:

Figure a: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT.

Figure b: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT.

Figure c: Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Morrisville, VT.

Figure d: Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Morrisville, VT.

References:

Drooz, A.T. 1985. Insects of Eastern Forests. USDA Forest Service Miscellaneous Publication 1426. p 204-205;

Johnson, W.T. and Lyon, H.H. 1991. Insects That Feed on Trees and Shrubs. 2nd edition. Cornell University Press. p 168-169;

Martineau, R. 1984. Insects Harmful to Forest Trees. Agriculture Canada Government Publishing Centre, Supply and Services, Ottawa. p 210-212;

Rose, A.H. and Lindquist, O.H. 1982. Insects of Eastern Hardwood Trees. Canadian Forest Service Publication, Forestry Technical Report 29. p 21-23.

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