HARPSWELL — Next spring, armies of parasitic flies will lay siege on the winter moth, an invasive species that threatens the town’s forests.

State entomologist Charlene Donahue said this is one of the efforts the Maine Forest Service is taking to control the winter moth population, in coordination with the U.S. Forest Service, the University of Maine and the University of Massachusetts.

Signs of the winter moth caterpillar were first reported in May – a grave concern because of the massive devastation the moth can cause in forests.

“They’ve been here for some time because of the amount of acreage that’s already affected and how severe it is in some places,” Donahue said in July.

Representatives from the agencies and universities visited Harpswell forests on Sept. 28 to decide where to place devices that will monitor the winter moth population and the general conditions of the forest, Donahue said.

He said the state and federal agencies will seek grants to fund prevention, monitoring and research efforts.

The University of Maine will monitor the effects winter moth has on the surrounding environment in Harpswell, Donahue said. The University of Massachusetts already has helped the Maine Forest Service positively identify the winter moth caterpillar.

To control the winter moth population, parasitic flies – known as cyzenis albicans – will be released into the forest.

Dr. Joseph Elkinton, a professor of environmental conservation at University of Massachusetts, said the flies will lay eggs on leaves in the spring, which the winter moth caterpillars will eat. The eggs will then hatch within the caterpillars, killing them before they create cocoons.

The newborn flies will then stay in the cocoons as shelter during the winter and emerge to lay eggs on leaves and begin the cruel cycle once again.

Elkinton said that because the flies rely on the caterpillar cocoons for winter survival, the fly population will naturally decrease when the winter moth does.

Donahue said that decreasing the winter moth population will take several years, but the species will never be fully exterminated.

“The winter moth won’t go away. It’s here,” he said. “This will just create an equilibrium so the impact is not as bad.”

Dylan Martin can be reached at 781-3661 ext. 100 or [email protected]. Follow him on Twitter: @DylanLJMartin.

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