Concerns don't stop attack on moth

April 30, 1995|By Mike Klingaman | Mike Klingaman,Sun Staff Writer

Maryland's spraying program to control gypsy moths begins at dawn tomorrow despite concern about the long-range environmental impact of one insecticide used by the state to control the tree-killing insects.

A three-year field study of the chemical Dimilin raises questions about wildlife safety in hardwood forests where that substance is sprayed, say West Virginia University scientists who participated in the $1 million federally funded project near Parsons, W.Va.

Among their findings:

* Though targeted for gypsy moths, Dimilin wipes out other creatures, including benign types of caterpillars, spiders and sawflies, some of which take years to recover.

* Stripped of their food banks, songbirds in Dimilin-treated areas struggle to feed themselves and their young. Migratory species such as warblers, tanagers and vireos were found to have less body fat than birds in unsprayed areas.

* Dimilin breaks down less rapidly in the environment than had been thought. About 40 percent of the chemical residue sprayed on hardwood foliage this spring will remain when the leaves fall in autumn, and 20 percent will last the winter.

"We had believed the impacts were short-term," says Richard Reardon, the U.S. Forest Service official who managed the project. Results will be published this year.

"Dimilin is very effective in killing gypsy moths, but it is also a very persistent pesticide," says Dr. Mary Wimmer, a WVU biochemist who took part in the research. "It sticks around for a long time."

The chemical also harms some marine life, she says. For example, Dimilin has been found to suppress populations of crawfish and shrimp.

Dimilin, whose active ingredient is Diflubenzuron, a synthetic growth inhibitor, kills moths and other molting insects at the larval stage by disrupting skin growth. Manufactured in the Netherlands and distributed in the United States by Uniroyal, the chemical poses no direct threat to man and other mammals.

"Dimilin doesn't kill the animals that people care about, which makes it OK with the general public," says Dr. Robert Whitmore, a wildlife ecologist at West Virginia who has studied Dimilin's effects for a decade. "But if it doesn't kill birds, it kills the birds' food -- and that is a serious environmental issue."

In the next two weeks, Maryland plans to spray 64,000 acres of woodland to suppress the gypsy moth, which last year #i defoliated more than 93,000 acres of woodland -- mostly on the Eastern Shore -- and destroyed an estimated $14 million worth of hardwoods in the state.

Forty percent of the 64,000 acres will be treated with Dimilin; the other 60 percent, including most infested tracts in the Baltimore area, will be sprayed with Bacillus thuringiensis (Bt), a naturally occurring bacterial agent that, when ingested, kills moth larvae. Though Bt is less effective than Dimilin, it dissipates quickly in the environment, is less harmful to other insect species and poses no hazard to aquatic life.

Maryland's three-week spray program addresses the risks associated with Dimilin, says Bob Tichenor, chief of the forest pest management section. He says the state uses only Bt to treat acreage with ponds or streams. No woodland is sprayed without consulting the Maryland Natural Heritage Program, a Department of Natural Resources office that monitors rare and endangered species of animals and plants, he says.

"We have to be mindful of where we're using these sprays," he says. "Dimilin's impact on nontarget species is a given, but we're not sure how toxic the residue is.

"There's no perfect solution. You've got to weigh your choices. Life is going to be rough on these birds anyway, if the trees they live in are dead next year."

As for the crab population of the Chesapeake Bay, he says, "There would be a problem if they were exposed to high enough concentrations, but what little Dimilin gets into the bay is almost undetectable. We've monitored it -- we're talking parts per trillion. And we don't spray right up to water."

Maryland's spraying is handled by contractors based in Frederick, Gettysburg, Pa., and Oregon, all hired by the state. Spraying is done early, when the air is calm.

Helicopters and fixed-wing aircraft, flying 50 feet above the treetops, release the spray. It takes 10 to 15 minutes for the mist to settle on trees or land, and half an hour more for the substance to dry, says Mr. Tichenor.

For those concerned about contact with the spray, "Wait 30 minutes after the aircraft is gone, and your exposure is minimal," he says.

More than half the battle (34,314 acres) will be fought on the Eastern Shore, starting with the Easton area in Talbot County and Hebron in Wicomico County. Also scheduled tomorrow: hot spots in rural southwestern Charles County, in southern Maryland.

Spraying coincides with the moths' first stirrings of spring. Egg masses laid last year are hatching, each mass releasing hundreds of caterpillars. Some start munching leaves immediately -- ingesting the insecticides at the same time.

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