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College of Food, Agricultural, and Environmental Sciences


Gypsy Moth Populations Increasing in Ohio

December 10, 2001

WOOSTER, Ohio - More than 42,000 acres of Ohio's forests were defoliated by the gypsy moth in 2001, nearly twice the amount of damage that occurred in 2000, according to Ohio Department of Agriculture (ODA) statistics.

Dan Herms, an Ohio State University entomologist with the Ohio Agricultural Research and Development Center, said much of that damage represents gypsy moth expansion into eastern and southeastern Ohio, regions of prime oak forests officials feared the insect would eventually inhabit.

"Obviously we are not happy at all that the gypsy moth has spread into southern Ohio. We have been dreading this situation for a long time," said Herms. "I'd say within the next five years, we'll see severe and widespread defoliation."

One area officials fear will be hardest hit is Hocking Hills, a region in southeastern Ohio that boasts some of the most widely visited state parks and forests. "The ODA is already finding high trap numbers in Hocking Hills," said Herms, expressing concern that some of the more environmentally sensitive trees will not be able to withstand repeated gypsy moth attacks. "If hemlocks are defoliated more than once, they'll probably die. Conifers are not as tolerant as deciduous trees are, which usually die only after two or three successive years of defoliation."

The gypsy moth is an invasive insect that has spread from the New England states into Michigan, Pennsylvania and Ohio throughout the past 130 years since it was accidentally introduced from Europe. It feeds on more than 100 species of deciduous and evergreen trees, severely damaging the trees, or in some cases, killing them. Over 1,100 trees were killed from gypsy moth attacks this year.

To date, 42 of Ohio's 88 counties contain established gypsy moth populations. The insect's habitat encompasses the uppermost western counties and spreads east through central Ohio to the southern boundaries of Hocking and Athens counties.

Some of the counties hit hardest by defoliation this year include Cochocton with over 11,000 acres defoliated; Licking and Tuscarawas, both with more than 6,000 acres; Harrison with nearly 4,000 acres; and Lucas and Muskingum, both with more than 2,000 acres. Only 400 acres of severely defoliated trees were recorded in Wayne County. Franklin County didn't even make the list, although a severe isolated infestation was sprayed in 2001 by ODA.

Herms said gypsy moth populations in central and northeast Ohio declined this year with the help of Entomophaga maimaiga, a natural fungal disease that can kill the gypsy moth in large numbers when environmental conditions are right.

"It rained almost every day in those areas from mid-May through mid-June, keeping it wet enough for the fungal spores to germinate and attack gypsy moth populations," said Herms. "We couldn't have asked for better timing than that. If the gypsy moths didn't die from the aerial Bt sprays, they were hammered by the fungal disease."

ODA's 2001 Gypsy Moth Suppression Program, which included egg mass surveys and aerial treatments using the insecticides Bt and Dimilin, resulted in a 93 percent reduction in egg mass densities throughout counties in northeast Ohio.

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Candace Pollock
Dan Herms