Larva Population Up After Recent Declines
By Nick Miroff
Washington Post Staff Writer
Sunday, May 13, 2007
Prince William is back at war with the rascally gypsy moth, a voracious, leaf-munching scourge that looks like a mustache and eats like an elephant.
Public works officials began an "aerial suppression" campaign Thursday, planning to spray about 4,000 acres throughout the county over the next week or so. It's the first time since 2004 that the county has had to hire aircraft to spray for the pests.
"If they're not controlled, they can literally defoliate an entire section of trees," said Wade Hugh, assistant director of public works. "We have to be able to keep them in check."
The county has 15 target areas, or blocks, where it's spraying an Environmental Protection Agency-approved insecticide from a low-flying, yellow crop-duster-style plane. Residents living in and around the areas have been notified by mail, with advisories that people and pets should remain indoors for 30 to 45 minutes after the spraying is complete and planes are no longer buzzing overhead. The spraying will not occur during times when children are walking to school or waiting for school buses.
"It's a precautionary measure," said Karen Walker, an entomologist who heads the county's program to control gypsy moths and mosquitoes. "The chemical isn't harmful to human beings, but there may be some people with higher sensitivities."
The operation will cost the county about $72,000 this year, and though the 4,000-acre effort is an increase over the 3,000 acres treated in 2004, it's far less territory than the county has treated in the past. Prince William has often topped the state in gypsy moth abatement efforts, but this year Fairfax County is spraying more.
Over the years, gypsy moth populations have dipped and surged, and researchers are trying to figure out how to best manage the insect, a Eurasian species introduced in Massachusetts by a French scientist in the 1860s. The bushy caterpillars with blue and red spots first appeared in Virginia in Shenandoah National Park in 1969, and have since defoliated hundreds of thousands of acres of forest, according to a Virginia Tech Web site devoted the critter.
"It's something that entomologists haven't figured out how to get rid of," Walker said. "No matter how much we try to suppress the population, they come back."
"Right now they're starting to creep up again," she said.
A naturally occurring fungus periodically diminishes gypsy moth numbers, so aerial spraying has not been necessary in recent years, Walker said. But she predicts even more larvae next year. When the caterpillars appear at this stage of the spring, they eagerly devour the leaves of local hardwoods and can kill trees. Oak leaves are a favorite meal.
On Friday, spraying was cut short because the insecticide used, Bacillus thuringiensis kurstaki, evaporates too quickly when temperatures rise above 75 degrees. Rain and high wind also can postpone spraying. But if weather conditions cooperate, then the spraying covers the foliage that the gypsy moth eats and delivers a deadly poison.
"It's toxic to their digestive system and makes it so they can't eat anymore, so they die from starvation after a couple days," Walker said.
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