People who know bugs and trees say there could be an upside to the sustained freezing temperatures that have challenged Mainers for more than a month, besides providing ideal conditions for ice fishing and pond hockey.

The daunting cold could tamp down insect populations that threaten backyard landscapes and woodlands across Maine, according to entomologists and tree experts.

The devastating winter moth and hemlock woolly adelgid – and possibly the brown-tail moth and spruce budworm – may be especially susceptible to subzero temperatures that set in just after Christmas, said Jim Dill, a pest management specialist at the University of Maine Cooperative Extension.

Unfortunately, Dill said, pesky and sometimes disease-carrying ticks, mosquitoes and fleas likely won’t be affected. They’re either hitching a ride on warm-blooded creatures, dormant in ice-covered swamps and ponds, or hidden in topsoil beneath the snow, where decomposing leaf litter can push temperatures above freezing.

“Insects above ground or in trees could be affected,” said Dill, an entomologist. “This cold isn’t doing anything to insects that overwinter in the ground. The snow’s going to insulate them.”

Except for a few days last week when temperatures rose into the 40s, Maine has been stuck in a deep freeze since Christmas Day, kicking off 2018 with a run of record-setting lows. A stretch of below-freezing temperatures that started in mid-December resumed Saturday and is expected to continue through Thursday.

Dill said the severe cold has put a major kink in the winter moth’s mating season, which runs from Thanksgiving through January.

“About half of their mating season has been disrupted,” he said, which could mean about half as many eggs have been laid.


Winter moths – whose caterpillars hatch in the spring to feed on oak, maple, ash, elm and fruit tree leaves – typically emerge from the ground to mate and lay eggs whenever the temperature rises above freezing. But winter moth traps in Cape Elizabeth and Harpswell have been empty since Dec. 11, when temperatures dropped below 32 degrees and pretty much stayed there.

“They haven’t seen any moths since then,” said Charlene Donahue, an entomologist with the Maine Forest Service and president of the Maine Entomological Society.

An icy crust on significant snow cover also stymied winter moth activity, Donahue said, because they “can crawl through 10 inches of fluffy stuff” when warm temperatures beckon.

Cape Elizabeth is ground zero in Maine for the winter moth, which has damaged or killed thousands of trees from Kittery to Bar Harbor since 2011. A recent aerial survey found 300 acres of oak mortality in Cape Elizabeth – an area encompassing 2,000 to 3,000 dead trees – and the infestation has spread into South Portland and Scarborough.

Todd Robbins, Cape Elizabeth’s tree warden, said he hopes the extended cold will knock back the winter moth population, but he knows it won’t harm eggs that were laid on trees in late November and early December, when temperatures hovered in the 40s and 50s.

“On the warmest days, we had crazy (winter moth) activity. People were reporting clouds of them,” said Robbins, a licensed arborist who works at Ram Island Farm. “Since the cold snap, we’ve seen nothing. I wish we had gotten it sooner.”

Constant freezing temperatures also could impact the hemplock woolly adelgid, an aphid-like insect that is killing the graceful evergreens from Kittery to Camden. Known for their cotton-white coverings, the tiny insects attach themselves to young hemlock branches and feed through the winter. Left unchecked, they can destroy a towering hemlock in a few years.

Because woolly adelgids are on tree branches, exposed to the elements, there’s a chance that some of the insects will be killed by severe cold. However, without targeted pesticide applications or other interventions, an adelgid infestation will rebound from any losses, Donahue said.

“Extreme cold sets them back, but it won’t get rid of them,” she said.


Also susceptible to freezing temperatures are spruce budworms and brown-tail moths. Budworms are found across northern Maine, where they defoliate fir and spruce trees and overwinter in cocoons spun in the crevices of treetops.

While budworms are wreaking havoc in the forests of Quebec and New Brunswick, Dill said, Maine’s budworm population has been relatively stable, and severe cold may help keep them in check.

Brown-tail larvae feed on hardwood leaves and spin tell-tale winter webs at the end of tree branches along the southern Maine coast.

“Winter cold doesn’t really affect the brown-tail moth,” Donahue said. “But this cold has been extreme, so there may be an impact, and we’ll be looking for that.”

Chuck Lubelczyk, a field biologist with the Lyme & Vector-Borne Disease Laboratory at the Maine Medical Center Research Institute in Scarborough, agreed that the deep cold likely won’t affect insects in ground covered by snow or water covered by ice – both typical winter conditions in Maine.

The lab has a Lyme disease research site in Cape Elizabeth, where scientists are studying tick activity and mortality under various environmental conditions, including designated areas without snowcover where die-offs have been significant in recent years.

And while severe cold probably won’t impact mosquito populations, recent dry summers will, Lubelczyk said. Maine has experienced drought conditions the last two summers, drying up swampy areas where the insects typically flourish.

“We’re seeing fewer mosquitoes overall because of drought,” Lubelczyk said.

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