This spring, winter moths may dominate

Severe outbreak expected in region

By Stefanie Geisler
Globe Correspondent / April 15, 2010

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This spring, trillions of winter moth caterpillars are expected to nibble and chomp their way through leaves in Massachusetts. According to scientists, that population could be the highest ever seen in this area.

“It’s going to look like a lot of shotgun blasts went through the leaves in these neighborhoods, if the trees aren’t completely defoliated,’’ said George Boettner, a laboratory technician who works under Dr. Joseph Elkinton at the University of Massachusetts Amherst.

Elkinton is an entomology professor who focuses on population dynamics. His laboratory has been studying winter moths since 2004.

The last severe outbreak was in 2005, when about 100,000 acres of trees were defoliated, Boettner said.

“This one’s probably going to surpass it, because the winter moth is actually spreading farther and farther west in Massachusetts,’’ Boettner said. “We think it’s moving maybe 7 or 8 kilometers a year. It’s going to become a bigger and bigger problem.’’

James McGuire, president of Hartney Greymont, a tree and landscaping company based in Needham, said he has already seen the tiny inchworms in the area.

“They’re expecting this to be one of the heaviest years for the winter moth. That’s what they’ve been telling us all winter,’’ McGuire said. “They are definitely out. We started seeing them or finding them almost two weeks ago.’’

Winter moth caterpillars burrow into the buds of deciduous trees and shrubs, including maples, oaks, apples, crabapples, and blueberry bushes. Once inside, they begin to feast.

On average, there are about 250,000 caterpillars per tree, Boettner said.

“It’s phenomenal,’’ he said. “We could literally have four trees and a million caterpillars between them.’’

After hatching, the caterpillars are tiny enough to fit on the head of a pin. They grow up to an inch long.

The winter moth has infested about a million and a half acres of trees in Massachusetts, Rhode Island, Maine, New Hampshire, Connecticut, and New York, Boettner said. Eastern Massachusetts and Rhode Island have been hit hardest.

Because it is not native to this area, the winter moth has no natural predators. But for the past five years, researchers at Elkinton’s lab have been trying out a solution that has worked in Europe, Nova Scotia, and British Columbia.

“We know how to combat it,’’ Boettner said. “This moth is in Europe, and it is actually controlled by a species-specific fly that hunts it down.’’

The parasitic flies, known as Cyzenis albicans, are attracted to the saliva of winter moth caterpillars. They lay their eggs where a caterpillar is feeding.

“The caterpillar then consumes the egg, which is teeny tiny,’’ Boettner said. “It hatches within 15 minutes and basically just hangs out there while the caterpillar gets fatter.’’

The fly begins to devour the caterpillar from the inside, eventually killing it. The flies are unlikely to cause harm to other critters because they do not hatch in any other species, Boettner said. The eggs do not even hatch in Bruce spanworm, a moth native to this area. It is closely related to the winter moth species.

“The flies are completely tied to their host,’’ Boettner said. “Their only mission in life is to hunt down winter moths and lay eggs in front of them.’’

Since 2005, the parasitic flies have been released in conjunction with the Massachusetts Department of Conservation and Recreation and the US Department of Agriculture. Today, they have been introduced to six areas in the eastern part of the state — Falmouth, Yarmouth, Seekonk, Hingham, Wellesley, and Wenham.

“Once those places are established, we’ll start filling in the gaps between them,’’ Boettner said.

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