As snow begins to cover the landscape, most insects in Maine have either died, fled or gone into hibernation. But not so for the aptly named winter moth, which emerges from the cold ground to take flight on winter nights.
New to the state of Maine, the winter moth, while intriguing, has the ability to damage forests, orchards and blueberry fields. During the past few years, state entomologists have been working to get a handle on this new population of pests, and they’re seeking help from the public this winter.
The Maine Forest Service is asking Maine residents to report any moth sightings from November through January online at maine.gov/dacf/wintermothsurvey . The quick online survey asks basic questions, such as when and where the moths were spotted.
“There’s an awful lot about these moths that we don’t know because they haven’t been here very long,” state forest entomologist Charlene Donahue said.
The winter moth, Operophthera brumata, was introduced to North America from Europe in the early part of the last century, according to the Maine Forest Service. But it wasn’t until the early 2000s that they made their way to New England, defoliating maple, oak and apple trees, as well as blueberry bushes.
Over several consecutive years, this defoliation leads to branch dieback and ultimately the death of entire trees. In fact, winter moth defoliation already has contributed to the destruction of tens of thousands of acres of oak trees in Massachusetts, according to the Maine Forest Service.
These destructive moths showed up in Maine in significant numbers for the first time in December of 2011, and entomologists already are starting to see their adverse effect to forest and backyard trees. This year, an aerial survey noted defoliation of trees in Cape Elizabeth, Portland, Peaks Island and Harpswell, according to a recent press release sent by the Maine Department of Agriculture, Conservation and Forestry. On the ground, defoliation could be seen in scattered locations from Kittery to Rockland.
“The total economic impact of Maine’s forest industry is $8 billion, with direct and indirect employment of 38,789 workers,” Gov. Paul LePage stated in the press release. “Fighting invasive insects like the winter moth is important to help protect that sector of our economy; in this case, hardwood trees and agricultural crops such as apples and blueberries. Public involvement will help professionals combat and minimize the destructive potential of this and other invasive species.”
Fortunately, one thing that has proven effective in controlling the winter moth population: a tiny fly called Cyzenis albicans.
“The fly is one of the things that keep the winter moth under control in Europe,” Donahue explained.
Originally from Europe, Cyzenis albicans has been used in the U.S. and Canada to combat winter moth populations. These flies are being reared by the University of Massachusetts as biocontrol agents, which already have been put to use in Maine. In the spring of 2013 and 2014, the Maine Forest Service worked with UMass to release the flies in Harpswell, Cape Elizabeth, Kittery and Vinalhaven.
“They don’t bother people,” Donahue said of the foreign fly. “They don’t even bother other insects. They are very specific to winter moths because of their life cycle.”
After being released in the spring, Cyzenis albicans females lay hundreds of eggs on damaged oak leaves. These eggs are eaten by winter moth caterpillars, which eat the foliage of specific trees throughout the spring, then drop to the ground in June to form a cocoon in the soil. It isn’t until the moth has formed a cocoon that the Cyzenis albicans larvae makes its move, eating the moth and taking over the shelter until the following year, when it emerges as an adult fly.
This winter’s public survey on moth sightings will help the Maine Forest Service determine where in Maine to release these biocontrol agents.
“This time of year, many of us are still out and about after dark,” Donahue said. “Even if we aren’t, we may cast a glance at our windows and notice if there are several or more small tan moths trying to get to our indoor lights.”
Another way state entomologists are learning about the winter moth population in Maine is by catching them in traps.
The Maine Forest Service spent part of the first week of December setting up moth traps along the coast and inland in southern Maine. Towns in the study region are cooperating by allowing traps to be hung on municipal property, and two homeowners in the most heavily infested areas have volunteered to make nightly counts of the moths trapped in their yards.
“A healthy forest is key to Maine’s forest economy,” stated Walt Whitcomb, Commissioner of the Maine Department of Agriculture, Conservation and Forestry in a recent press release. “Having citizen involvement in monitoring invasive pests is important to the future of rural Maine.”
Adult winter moths emerge from their cocoons in November and December and remain active until January, whenever the temperature is above freezing. The males are small, light brown ordinary-looking moths; while females are small, gray and flightless because of their greatly reduced wings.
Females are often found crawling on trees, where they emit a pheromone to attract males. Once mated, the female lays 150 eggs, then dies. The male dies soon after as well, according to a fact sheet on winter moths provided by the UMass Agriculture and Landscape Program.
While winter moths are particularly rugged insects, they are also affected by severe cold and heavy snow cover and ice, Donahue said.
“Last winter, when it got really cold in December, it really seemed to reduce populations from what they were before,” she said.
The recent appearance of winter moths in Maine may have to do with warmer winters, as well as people transplanting gardens to Maine summer homes. While in their cocoons, the moths can be transported in soil.
“The places where winter moths have gotten a foothold in the largest numbers tend to be communities that have large numbers of second homes,” Donahue said.
Given the early ice and snow this winter, Donahue said there’s a good chance the population will remain low in Maine for the time being.
The winter moth survey can be accessed at maine.gov/dacf/wintermothsurvey. Reports of moth flights can also be made by phone at 287-2431.