This insect’s most obvious sign is a silken “tent,” or mat in the case of the forest tent caterpillar, that can be seen among the branches of a tree (Figure 1). These tents can be a foot or more long, and they can be used by dozens of larvae. The larvae use the tent for resting and for protection from predators and weather extremes. A larva leaves the tent daily to feed on the tree’s foliage for four to six weeks before finding a protected place suitable for forming a cocoon. After two to three weeks, the insect emerges as an adult (moth) and no longer feeds on tree foliage. After mating, the female moth finds a suitable host tree and deposits egg masses of 150 to 300 eggs, often in a band around a twig (Figure 2). The eggs hatch shortly thereafter, but the larvae remain dormant in the eggs until the following spring. There is one generation per year.
In some cases, patches of trees and forested areas can be defoliated, and defoliation may occur several years in a row. Most trees can survive the loss of foliage and will leaf out again in the summer with a tougher, less palatable leaf. Trees in poor condition that are stressed by disease or drought may be more susceptible to mortality. While significant economic impacts in forest or fruit production are not widely reported, eastern tent caterpillars have been associated with Mare Reproductive Loss Syndrome in Kentucky.
In smaller landscape settings, mechanical control includes pruning out and destroying the tents in the early spring when caterpillar activity begins, preferably in the early morning when many caterpillars are still in the tents. Egg masses can be pruned during the winter when they are visible, especially on smaller trees.
Insecticidal control includes the use of Bacillus thuringiensis (Bt), as well as other botanical or synthetic insecticides. Bt is a naturally occurring bacterial organism that kills the larvae of moths and butterflies. It is available as an insecticide under several brand names. It is nontoxic to humans and other nontarget organisms, such as bees and fish. Experts recommend applying chemicals on budding foliage in the early spring when caterpillar activity begins so that small, early-stage larvae consume the insecticide while feeding. In events where large populations are hard to control, the use of insecticides is not necessarily more effective than natural causes and the use of the mechanical control methods mentioned above.
Day, E.R. 2002. Eastern Tent Caterpillar. Virginia Cooperative Extension. Publication 444-274W.
DeGomez, T.E. 2009. Tent Caterpillars in Northern Arizona above 6000 Foot Elevations. University of Arizona Cooperative Extension. Publication AZ1249.
Dill, J.F., and C.A. Kirby. 2010. Fact Sheets—Forest and Eastern Tent Caterpillars. University of Maine Cooperative Extension. Pest Management Fact Sheet #5022.
Meeker, J.R. 2011. Forest Tent Caterpillar, Malacosoma disstria Hübner (Insecta: Lepidoptera: Lasiocampidae). University of Florida, Cooperative Extension Service, Institute of Food and Agriculture Sciences. Publication EENY-184.
USDA Forest Service. 2013. National Forest Health Monitoring Program. http://fhm.fs.fed.us/
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