HARPSWELL — Buckets of pesticides, home-grown parasitic flies, and DNA testing are all likely to be employed in the battle against the invasive winter moth, which was positively identified in town last month by dismayed state conservation officials.

The small brown moth, which has a wingspan of a little more than an inch, can ravage apple trees, blueberry bushes, and hardwoods, all of which adds up to bad news for the state’s agriculture, forestry, and tourism industries.

Connie Sweetser owns an apple orchard that is uncomfortably close to the infested acreage – 400 acres of real estate spanning hundreds of private properties, including a chunk of Harpswell Neck and a section of Orr’s Island. 

Sweetser’s Apple Barrel and Orchards, in Cumberland Center, is 35 miles away by car, but only 10 miles as the crow flies.

She said she was aware of the winter moths, but she’s waiting to hear from the state before deciding what to do.

“We’ll see what they have to say,” she said.

Charlene Donahue, a Maine Forest Service entomologist in the Maine Department of Conservation, documented the winter moth infestation after hearing from a concerned property owner late last year.

“She said there were just clouds of them,” Donahue said.

Winter moths spend November and December as moths; their eggs hatch into hungry caterpillars in the springtime, and that’s when the voracious pests do their damage, chewing their way through so many leaves and buds that the host tree can die.

One of the great mysteries surrounding the winter moth involves its closely related cousin, the native bruce spanworm.

Scientists have such a difficult time differentiating between the two species that, in order to positively identify the winter moth population in Harpswell, Donahue had to collect specimens and have them sent to the University of Massachusetts for DNA testing.

Therein lies the mystery: Why is it that the native spanworm is held in check by natural predators, while the virtually identical winter moth runs amok?

Both species are preyed upon by many natural predators. Moths and caterpillars are beset by a wide variety of birds. In between, as pupa, they are eaten in large numbers by oil beetles, ground beetles, moles and mice. In addition, they are a favorite host for parasitic wasps, which lay their eggs in the caterpillar, setting the stage for the young maggots to eat the caterpillar from the inside out.

But for some unknown reason, bruce spanworms rarely get out of hand, while winter moths frequently proliferate to the extent that they destroy large numbers of oak, elm, maple, ash, and crabapple trees.

Donahue is studying the problem in the hope that she can unlock the difference. She is working with residents in the unorganized township T2 R8 NWP, near Lincoln, which has seen high numbers of bruce spanworms this year.

If she identifies the spanworm’s hidden weak spot, it could give conservation officials in Maine and Massachusetts, which is overrun with the winter moth, a clue as to how to defeat the pest.

No one knows for sure how the winter moth made its way to Maine. The caterpillar typically disperse by a process called ballooning, which sees them spinning strands of silk that pick up the wind and carry them away.

It’s an effective method of travel, but Donahue said that it’s not likely to have carried them the hundreds of miles from Massachusetts to Harpswell.

Instead, she said, the culprit is likely another species, a large primate that is known to summer in Maine before heading south for warmer climes in the winter. 


“The way they get around the most is in landscape plants and in moving trees,” said Donahue. “You’re moving the pupa with the plants in the soil. If people don’t move landscape plants around, they won’t get infested.”

She said she suspects that several years ago, a few pesky winter moth pupa or caterpillars hitched a ride into Maine on a plant carried by a seasonal homeowner.

Those few invasive pioneers needed time and luck to survive and breed, but over several life cycles, they established themselves in Harpswell.

Donahue said it would have taken years for the pest to build up to the infestation level seen today.

Because of the winter moth’s presence, Harpswell citizens are being asked not to take landscaping plants or firewood out of town, which could inadvertently spread the problem to other parts of Maine.

The problem took years to develop, and Donahue said that it will take years to fix.

“Life is not a microwave,” she said.

The current plan is to release hundreds of parasitic flies, known as cyzenis albicans, into the environment, in the hope that they can reduce the number of winter moths.

It could take five years just for the flies to establish themselves, Donahue said, and years more before they catch up to the burgeoning population of winter moths.

Even if the program is wildly successful, it won’t eliminate the invasive species altogether. But it will prevent them from thriving in such numbers that they can kill trees.

The European species first came to North America in the 1930s in Nova Scotia; 20 years ago, it flourished in eastern Massachusetts, and scientists say it is spreading into Rhode Island and Connecticut.

Control efforts involving the parasitic flies have been successful in other parts of the country, and Donahue said she hopes that success will be replicated in Maine.

Matt Hongoltz-Hetling can be reached at 781-3661 ext. 123 or [email protected]. Follow him on Twitter: @hh_matt.

Sidebar Elements

The invasive winter moth caterpillar was discovered in Harpswell in late May. Scientists say the species, which was likely brought to Maine on a landscaping plant, is a threat to hardwoods, apples trees and blueberry bushes.

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