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WOOSTER, Ohio - As the gypsy moth caterpillar feeds and matures over the next several weeks, the invasive insect shares Mother Nature's bounty with other caterpillar pests that look similar and feed on the same host trees, potentially confusing homeowners as to what exactly may be attacking their shade trees.
Dan Herms, an Ohio State University entomologist, said the gypsy moth caterpillar looks similar to and shares host trees with the eastern tent caterpillar (Malacosoma americanum), forest tent caterpillar (Malacosoma disstria) and the fall webworm (Hyphantria cunea), but the insects' life cycles differ.
"Eastern tent caterpillar is one of the most common caterpillar pests in Ohio, and gypsy moth is quickly joining its ranks" said Herms, who is based at OSU's Ohio Agricultural Research and Development Center in Wooster. "Eastern tent caterpillars mature about two to three weeks before gypsy moth. So by the time gypsy moth caterpillars reach maturity in mid-to late-June, the eastern tent will have already completed its development." The eastern tent caterpillar, easily recognized by the tent-like silk nests it builds at branch forks during spring, feeds primarily on cherries and crabapples, although older caterpillars can be found occasionally feeding on other trees, such as birch, maple, oak, and ash, especially when populations are high. A mature caterpillar is characterized by fine hairs, robin egg blue markings on its side and a distinct white stripe along its back. By comparison, a mature gypsy moth caterpillar is also hairy, but is dark with five pairs of blue dots and six pairs of red dots along its back.
Herms said the eastern tent caterpillar is native to Ohio and has many natural enemies, such as predaceous and parasitic insects, birds, small mammals, and diseases caused by viruses, bacteria, and fungi, which help to control outbreaks. "Even during heavy outbreaks, natural enemies help to control the insect, so they don't do the damage to trees that the gypsy moth can do," he said.
The forest tent caterpillar, which reaches high numbers occasionally in Ohio, also matures about two to three weeks earlier than the gypsy moth caterpillar. The forest tent caterpillar, which is closely related to and resembles the eastern tent caterpillar, is characterized by fine hairs, blue markings on its side and back and white "keyhole" markings on its back. It feeds on sweetgum, oak, birch, aspen, maple, elm and basswood, among others. Despite its name, the forest tent caterpillar does not produce a silk nest.
Herms said that although the forest tent caterpillar can be found in Ohio, it is more prevalent in northern Great Lake states like Michigan and into Canada.
The fall webworm, a caterpillar that feeds on over 100 species of deciduous trees, is active after the gypsy moth caterpillar pupates, becoming most obvious in August and September. The fall webworm spins silk nests in host trees and is characterized by silky hairs and pale green or yellow color with a black stripe on its back and yellow stripes on its sides.
Herms said the fall webworm also has natural enemies that help to keep outbreaks in check. "Plus, fall webworms develop so late in the season that defoliation has little impact on the health of trees," he said.
Eastern tent and forest tent caterpillars near the end of their larval stage in late May, while fall webworms shows up in July and peak in September. Gypsy moth caterpillars, which have been hatching from egg masses from late-April until the first week of May, will reach maturity in June and pupate into their adult moth forms in July.
For more information, log onto the Ohio Division of Natural Resources website at http://www.hcs.ohio-state.edu/ODNR/Health/forestpests.htm.