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April 19, 2014

Winter moths devastate hardwood trees on coast, islands

Pingree's office wants to keep funds in farm bill to provide response

by Tom Groening

The winter moth caterpillar feeding within silked-together leaves in Harpswell.
The winter moth caterpillar feeding within silked-together leaves in Harpswell. PHOTO: COURTESY MAINE FOREST SERVICE

VINALHAVEN — Town Manager Marjorie Stratton left the office and was on her way home one evening in November 2012 when she saw a flurry of white around a streetlight.

"Oh, it's snowing," she remembers thinking, but a moment later, she realized it wasn't a flurry but a swarm.

Male winter moths are known to fly in great numbers around lights, as they seek out the flightless females for mating. The insects, native to Europe, stand out at that time in Maine as the temperatures dip into the freezing range and other insects are on the decline or gone. But the moths are more than an aberration. State forestry officials say they also are an abomination.

During their larval stages, the moths eat through the folded-up leaves contained in hardwood tree buds, resulting in serious foliage damage.

Allison Kanoti, a forest entomologist with the Maine Forest Service, agrees with Stratton and others on Vinalhaven who say the island has seen defoliation in the last few years.

But the problem extends beyond the island.

"We do have records of winter moths from Kittery all the way to Mount Desert Island, with some smaller breaks in between," Kanoti said.

Last year, moderate to heavy damage was seen from Cape Elizabeth to Bristol, and from the Penobscot Bay region to Mount Desert Island. In all, some 5,100 acres have been deemed defoliated by the winter moth, Kanoti said.

The lifecycle begins in the spring.

In April, the insect's eggs hatch on host trees, and the caterpillars—about a millimeter long—crawl into the nascent buds. They chew away through late May or early June, then crawl down into the soil to pupate, Kanoti said. The moth version emerges in late November and early December. The moths are active as long as the temperature is above freezing, drawn to the flightless females by a pheromone.

While the caterpillar is buried in the ground, resting from its feast, those munched-over buds of the hardwood trees open. The leaves resemble Swiss cheese, and the tree's health may be compromised.

The winter moths were first seen in Nova Scotia in the 1930s, Kanoti said, probably arriving there in plant soils transported by ship. As much as 40 percent of the province's red oaks were devastated by the 1950s.

By the late 1990s, they were evident in Massachusetts, impacting oak stands in the eastern part of the state.

On Vinalhaven, fruit and other prized hardwood trees in yards sport odd-looking belts—a bat of Fiberglas insulation covered in reversed duct tape, a remedy that's supposed to inhibit the caterpillars from crawling up the tree trunk to the buds. But Kanoti says the best way to combat the moths is to introduce parasitic flies and wasps into the environment. Those insects lay their eggs on chewed foliage, and the fly and wasp caterpillars eat the winter moth eggs along with the leaf.
Without this introduced opponent, the winter moth will continue to expand because it has no natural enemies in North America.

Rep. Chellie Pingree, D-North Haven, has responded to a request for assistance from Stratton and Vinalhaven town officials. Money to pay for introducing the parasitic fly and wasp is included in the federal farm bill, and Pingree has fought efforts to cut those funds, her office has reported.



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