BATH — With the deep freeze gripping the state in recent days, it may be difficult to think about spring. But warming temperatures will bring the emergence of winter moth larvae, crawling to the tree tops and feeding voraciously on their leaves. It turns out the December cold may help in fighting the destructive insect, which, unlike the brown-tail moth, doesn’t make nests that are easily identified and destroyed.

Bath has been particularly hard hit in the Midcoast area by winter moth infestation in the last two years, along with Harpswell, according to Charlene Donahue, forest entomologist with Maine Forest Service.

“Bath has a far worse problem with winter moth, and Brunswick a worse problem with brown-tail moth,” she said. A map provided by Maine Forest Service shows the most affected areas. “There is a lot more damage that can be mapped from the air soon, as multiple trees have to be moderately to heavily defoliated before it is visible.”

Adult moths emerge from the soil in November and December, where they have burrowed in hard shells since June. The white, winged males seek the wingless brown females as the latter crawl into the trees; they mate, and the female lays hundreds of eggs. The adults die, and the eggs hatch in spring, spawning tiny green inchworm-like caterpillars who eat their way through the tree buds, and balloon through the air on thin threads to other trees.

When they have finished feeding, around June, the caterpillars migrate to the soil, and pupate until November and December. With the recent icy stretch of weather, the mating season was stopped short, which could reduce the number of eggs laid.

“No one is really studying this, so I can’t be positive this affects populations,” Donahue said, observing how a late spring cold snap may also be helpful.

“Warm temperatures and then good freezes in late April/May can kill larvae that have emerged. And warm spring weather, followed by cold weather, can allow larvae to hatch and then delay bud development so the larvae starve. Again, no one is really studying any of this, so it’s just observations.”

City of Bath Arborist Kyle Rosenberg hosted workshops earlier last year on wrapping troubled trees in strips that are then covered with a sticky substance called Tanglefoot. This process helps slow down winter moth mating, trapping the adult moths on the strip.

“I think the tree wrapping workshop went well,” he said, noting the “explosion” of winter moth in 2017. “Next season we’ll step up our promotion of the class. I believe we had 33 people show up, and looking around town, it’s safe to say many folks went ahead and wrapped their trees and perhaps even got their neighbors on board. Making it a community project will greatly help reduce the number of eggs laid this fall.”

Amanda Walden banded a dozen trees on her family’s property near downtown Bath in November. Two large red maple trees were of significant concern.

“I caught so many females on those two red maples that I ended up putting a third strip of Tanglefoot in between the two strips on there,” she said. “Those two trees were covered in female moths when I took the bands down and redid them after a week or two. I’m not sure how many were caught, but it sure seemed like thousands.”

Walden wonders if those maples were at the epicenter of the city’s infestation. “I haven’t seen any other full bands like that around town,” she said.

Curious as to whether any sticky substance besides Tanglefoot might work when she re-banded some of the trees, Walden tried petroleum jelly. She’s done the research for you: “The petroleum jelly didn’t catch a single female, so Tanglefoot is definitely the way to go.”

Rosenberg says that plans are under way for a two-pronged attack in Bath next year.

For the first time, some of the larger trees in the city’s parks and downtown areas will receive injections of ememectin benzoate, which is a widely used insecticide.

“Since a number of the trees are apt to be impacted by brown-tail moth, using the emamectin benzoate will also help to manage the late summer stage of that pest,” Rosenberg said.

Secondly, Bath will see the release of the Cyzenis albicans parasitic fly in 2018. The moth larvae eat the flies’ eggs, and then die when the eggs hatch inside of them.

“If the cocoons are available from UMass next year, and if the winter moth population is high enough to support the parasitoids, than there will be a release of the flies in fall,” Donahue said, adding that it seems likely.

Releases have been made in Cape Elizabeth, Harpswell, Kittery, Peaks Island , South Portland and Vinalhaven starting in 2013. Donahue said that it takes seven to 10 years or more for the fly populations to start having an effect on the winter moth.

“The fly numbers have to catch up with the winter moth numbers. Only 1,000 to 3,000 flies are released per site, and half are males, so even with the females laying 100 eggs or more, it still takes time.”

Donahue added that people should not move dirt in their garden from June through December, as the pupating moths from infected trees will be moved with it. She asks that people seeing winter moths report their sightings at www.maine.gov/dacf/wintermothsurvey.