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State battles winter moth with parasitic flies in Harpswell, Cape Elizabeth

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State battles winter moth with parasitic flies in Harpswell, Cape Elizabeth

HARPSWELL — Over the next few months, two Maine communities will become the battlegrounds in the war against insects.

The state last week introduced hundreds of parasitic flies in Harpswell and Cape Elizabeth, in an attempt to decimate the winter moth, an invasive species that poses a threat to Maine's forests.

Winter moths have been found along the coast from Kittery to Bar Harbor, but Harpswell and Cape Elizabeth have been marked by the state as two of the most densely populated areas, where the threat of tree defoliation is high.

On May 9, state entomologist Charlene Donahue pulled her car into the driveway of Eartheart Gardens on Harpswell Neck Road. In tow were nearly 1,000 parasitic flies, or cyzenis albicans, that will begin their slow attack on the winter moth this week.

The proprerty's owners, Sharon Whitney and Don Clifford, and their neighbors allowed the state to use a wooded area in their backyard to battle the invasive moths.

Whitney said the winter moth's presence has hurt some local businesses, including her own garden nursery, because the moth cocoons can often be found in plant soil.

"I will not send out any plants of the nursery that might have winter moths," she said. "... It really eats into my bottom line."

Donahue said because winter moth larvae spin their cocoons in the ground and surround them with dirt, it puts gardeners at a high risk of spreading winter moth to other areas when they move plants.

"It's hard to differentiate winter moth cocoons from the dirt," Donahue said, which is probably why they reached Maine in the first place.

It's also for that reason Whitney hasn't been able to sell some of her plants since winter moths were identified in town in 2011. She said even the Harpswell Garden Club had to cancel two fundraising events in the past year because the risk of spreading the invasive species was too high.

Whitney said she hopes that will change with the state's latest efforts.

After Donahue unloaded the two boxes of parasitic flies from her car, she and and Kaitlyn O'Donnell, a University of Maine graduate student, began loading the flies into a narrow netted tent.

The flies stay in the tent for a week, until they are ready to mate and begin the process to slowly reduce the winter moth population.

"They have a very special job to do," Donahue said.

Later this month, the flies will lay eggs on the leaves of nearby trees, which will then be eaten by the winter moth larvae. Once the larvae spin their cocoons into the ground and pupate, the fly larvae will hatch and eat the pupa from the inside out. The flies then remain in the cocoon over the winter, and emerge as adults the next spring to restart the deadly cycle.

Because the fly species relies on the moth's cocoon for survival, Donahue said, its population will dwindle along with the moth's population.

In five years, the state expects the winter moth populations will decline to a point where they no longer pose a threat.

While some of O'Donnell's work is for her own entomology thesis on the impact of winter moths, both she and Donahue are aiding a larger research effort by the University of Massachusetts at Amherst.

The university provided the flies for Cape Elizabeth and Harpswell in order to measure their effectiveness against winter moth in different areas across the country, Donahue said. The cost of the flies was funded by the U.S. Department of Agriculture and U.S. Forest Service.

Donahue said Massachusetts, in particular, has been hit hard with winter moths, which defoliated nearly 89,000 acres of trees in 2011.

The Maine Forest Service will conduct its own defoliation survey in June to further assess the threat from winter moths and other defoliators. 

Dylan Martin can be reached at 781-3661 ext. 100 or dmartin@theforecaster.net. Follow him on Twitter: @DylanLJMartin.