BATH

A s part of the ongoing battle against winter moths in the

Midcoast, an entomologist with the Maine Forest Service placed hundreds of parasitic flies in Bath to fight the invasive pests.

Winter moths have caused extensive damage to trees in the region since they were first discovered in the state back in 2012. As caterpillars, winter moths eat the leaves of trees and shrubs that shed leaves annually — such as oaks and apple trees — causing defoliation that can harm, and eventually kill, the trees over several years. While Bath City Arborist Kyle Rosenberg didn’t have an number of how many trees winter moth had damaged in the city, he estimated the insects had damaged 375 acres of forest.

Now, the city is partnering with the state to tackle the unwanted pest. Maine Forest Services entomologist Colleen Teerling placed a small screened box filled with 700 flies, which are currently in their winter cocoons, behind Grace Episcopal Church on Wednesday.

“They’re in the box to protect them from ground dwelling predators,” said Teerling. “That’s their biggest risk.”

In the spring, the box will be opened, releasing the flies to prey upon the winter moth. Teerling noted that the impact won’t be immediate, and it will take a while for the flies to spread out over the Midcoast.

The flies will lay eggs on the leaves that caterpillars feed on. The eggs will hatch inside the caterpillar, and the larvae will eat their way out. The fly will emerge as an adult and fly off to mate and start the cycle over again.

“We probably won’t be able to see any effect for two, three, four years,” said Teerling. “If we can continue to keep releasing them, you know, maybe in 10-15 years winter moth may not be that much of a problem in many places along the coast.”

The parasitic flies only target the winter moths. Like the winter moth, the flies are originally from Europe.

“This is about as close to a silver bullet as you get in biology,” said Teerling. “Life is never this good. I’m really excited about this.”

According to Teerling, the flies are a tried and true biocontrol agent, and have already drastically reduced winter moth populations in Massachusetts and Nova Scotia.

Rosenberg said they chose the Bath location because it is forested, isolated and unlikely to be disturbed. It’s also part of a small forested corridor in Bath that will help the insects spread out over the city.

While some residents might want a faster solution, that’s fast for a biocontrol agent, she added. For those looking for immediate relief from the winter moth, Bath will be holding a tree-banding class later this month where residents can learn how to wrap the trunks of their trees to prevent the caterpillars from climbing them.

“We did that last year and probably had 250 trees throughout this area banded,” said Rosenberg.

Because the flies only target the winter moth, other invasive species such as the browntail moth and the emerald ash borer won’t be affected.

The browntail moth has plagued Bath for several years. Like the winter moth, the browntail can also cause serious damage through defoliation, though it has the added feature of being covered with hundreds of tiny, barbed poisonous hairs that can cause rashes and breathing troubles in humans.

Teerling said that while the browntail moth is a major issue in the Bath area, it’s far less widespread in New England than the winter moth, which means there are fewer resources working toward their demise.

“It’s a big problem for Maine, but outside of Maine nobody’s ever heard of it,” said Teerling. “There’s just no funding for it.”

While other biocontrols, such as fungi, have curbed the browntail moth population at times, researchers have yet to find a silver bullet like they have for the winter moth.

Adding to the decimation of Maine forests is the emerald ash borer. An invasive species that can kill ash trees, the emerald ash borer has existed in bordering Canada and New Hampshire for years, but Maine was spared — until recently.

Earlier this year, the emerald ash borer was found in Aroostook County, and on Wednesday the Maine Department of Agriculture, Conservation and Forestry announced that the insect had been found in western York County.

Although the city of Bath is already working to mitigate the threat, it could take years for the insect to arrive in the city. The state claims that there are no practical ways to control the emerald ash borer population.

nstrout@timesrecord.com