Pest Identification & Damage
Common Name(s): Eastern Tent Caterpillar
Scientific Name: Malacosoma americanum (Fabr) Lepidoptera: Family Lasiocampidae. Similar species include the western tent caterpillar M. californicum (Packard); Pacific tent caterpillar, M. constrictum (Edwards); southwestern tent caterpillar, M. incurvum (Edwards); and Sonoran tent caterpillar, M. tigris (Dyar), the ranges of which are generally described by their common names. Flowering fruit trees (plum, wild plum, hawthorn) are the main hosts of the eastern tent caterpillar, although forest and shade trees including maples and oaks may be attacked.
Identifying Characteristics for Damaging Stage(s): Caterpillars are hairy, dark colored with a white dorsal stripe, longitudinal yellowish, orangish or brown lines on the sides and bright oval blue spots. They grow to 2 - 2½ inches long.
Damage/Nature and Symptoms: One or two colonies of larvae can defoliate small trees. During outbreak years, even larger trees may be stripped of leaves. Defoliation stresses trees, increasing their susceptibility to secondary pests and diseases and reducing fruit production. Trees are usually severely weakened only after 3 plus years of greater than 50% defoliation. Webbing reduces the aesthetic value of trees. Some people seem to suffer mental stress when they observe larval mass migrations in search of new food after defoliating the original host or in when caterpillars are in search of pupation sites.
Distribution and Life Cycle
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| Eastern Tent Caterpillar Nest |
Distribution: The eastern tent caterpillar is widely distributed in the U.S. east of the Rockies.
Summary of Life Cycle: Eastern tent caterpillars overwinter as collar-like dark brown masses of 150 to 400 or more eggs. The masses often reach ¾ of an inch in length and can completely encircle pencil sized twigs. Hatching occurs about the time wild cherry buds turn green in the spring. The gregarious larvae build a small silken web "tent" in a tree crotch for protection from the elements and predators. Almost blind, they leave the tent to feed on leaves during the cooler parts of the day, leaving a silk dragline as they move about the tree. Literature sources disagree somewhat at to the specific time of day that most feeding occurs, with one source stating that they are nocturnal to another saying they feed in early afternoon. Temperature, cloud cover; wind and larval stage (instar) may influence feeding time. The worms feed for about six weeks, after which they pupate in cocoons attached to tree trunks, other vertical surfaces, leaf litter or among grasses and debris on the ground. Pupation lasts about 2 - 4 weeks after which the reddish-brown moths, each with two whitish diagonal stripes on the forewings, emerge in late June or early July, mate and lay eggs for the next year. The eggs are covered by a foamy secretion that dries into a dark varnish-like protective covering. Only one generation occurs per year.
Management Methods:
Inspection/Survey Methods: Visually inspect susceptible trees after leaf drop in the fall for egg masses. Watch for the appearance of webs in early spring.
Non-Chemical Management Strategies: Natural enemies, especially birds such as orioles, ichneumonid wasps, braconids, and chalcids depress populations in some years. Orioles have been known to eat entire infestations. At least 24 species of parasitoids attack either the larval or pupal stages. Hand removal of egg masses during the winter and hand removal of tents during the summer provides control on small trees. Tents can be removed by simply winding them on a stick or they can be pruned out. Caterpillars can be killed by dropping them into soapy water. Wear gloves when handling caterpillars as their hairs are irritating to some people. Remove wild flowering fruit trees such as wild plum close to orchards. Keep trees in good condition by proper watering and fertilizing to raise their tolerance to insect feeding damage.
While some people actually burn the webbing out of trees, this is not a recommended practice due to the fire hazard and the damage burning does to tree branches.
Chemical Management Strategies: Chemical management is not often practical to control this nuisance pest on host trees. Bacillus thuringiensis (Bt kurstaki) products are effective and recommended to avoid hurting pollinators. Several insecticides are also effective but good coverage of larvae in the tent is difficult and beneficial insects are susceptible. One source recommended spraying in early morning when caterpillars are sunning themselves on the outside of the tent before dispersing to feed. Sprays should be applied as soon as caterpillars are noticed. Insecticides are not usually effective against mature larvae and Bt will not work on those that have stopped feeding and are searching for pupation sites as it must be ingested. In orchards, a normal spray schedule will prevent infestation by this insect.
For the latest information on available chemical controls, consult the Pesticide Selection Guide.
References:
Anon. 2001. No. 30 - Eastern Tent Caterpillar: Malacosoma americanum. Integrated Pest Management. University of Illinois. http://www.ipm.uiuc.edu/publications/infosheets/30-easterntent/easterntent.html
Anonymous, 4 Dec 1998. Eastern Tent Caterpillar. Michigan State University Extension. http://www.msue.msu.edu/msue/emp/mod02/01500620.html
Bessin, R. April 2003 (last visited) Eastern Tent Caterpillar. University of Kentucky College of Agriculture. http://www.unky.edu/Agriculture/Entomology/entfacts/trees/ef423.html
Davidson, R., and Lyon, W. 1987. Insect Pests of Farm, Garden, and Orchard 8th ed. John Wiley & Sons. New York.
Metcalf, C. L., W. P. Flint and R. L. Metcalf, 1962. Destructive and Useful Insects. 4th Ed.: McGraw-Hill Book Co., New York NY. 1087 p.
Sadof, C. April 2002. Eastern Tent Caterpillar. Hot News from the Department of Entomology. Purdue University Cooperative Extension Service. http://www.entm.purdue.edu/entomology/ext/targets/HN/HN-24/HN-24.pdf
Shetlar, D.J. April 4, 2003 (last visited) Eastern and Forest Tent Caterpillars and Their Control HYG-2022-95. Ohio State University Extension Fact Sheet.
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