SOUTH PORTLAND — City officials are developing a plan to fight destructive winter moth infestations that have begun to damage oaks, maples and other trees in neighborhoods next to Cape Elizabeth.

They’re working with entomologists with the Maine Forest Service, who were here Wednesday to release parasitoid flies as part of a regional project aimed at killing the small tan moths now seen flying around street lamps and porch lights.

While winter moths are visible in early winter their damage is done in the spring, when the eggs they lay on tree trunks hatch. maine.gov photo

The entomologists buried a cage filled with cocoons of the fly, Cyzenis albicans, on private property off Highland Avenue, near Hinckley Park, where winter moth caterpillars turned leafy canopies into lace last spring. The flies are expected to emerge next May and begin a months-long process of killing winter moths, their only prey.

“That’s an area of South Portland that’s experiencing a high rate of defoliation by winter moth,” said Charlene Donahue, a state entomologist. “The population is starting to spread out from Cape Elizabeth.”

Cape Elizabeth is ground zero in Maine for the invasive insect, which has damaged or killed thousands of trees from Kittery to Bar Harbor since 2011. An aerial survey last year 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.

“Hopefully, it won’t get to that point in South Portland,” Donahue said. “That’s why we’re expanding the biocontrol project.”

A SPREADING PROBLEM

Winter moths came to North America from Europe in the early 1900s. Infestations were seen first in Nova Scotia in the 1930s and then in the Pacific Northwest in the 1970s, according to the forest service. The moths arrived in Massachusetts in the early 2000s, spreading south into Rhode Island and north into Maine, likely transplanted with perennial flowers and shrubs from infested gardens.

The Maine Forest Service, with help from the University of Massachusetts and the U.S. Forest Service, previously released the flies in Cape Elizabeth, Harpswell, Kittery Point, Vinalhaven and Peaks Island, hoping to repeat successful moth population reductions in Nova Scotia and the Pacific Northwest.

The flies emerge in the spring and lay eggs on leaves that are eaten by winter moth caterpillars. The fly eggs then hatch into maggots inside the moth caterpillars and lie dormant until late summer, when they eat and kill the moth larvae as they pupate underground.

Donahue said it’s unclear how long it will take for the flies to have an effect on the local winter moth population, but it’s expected to take years. A recent survey of winter moth caterpillars in Kittery showed that 11 percent were infected and killed by the flies. The flies also are having an impact in Massachusetts, where they’ve been released since 2005.

‘ATTACKING FROM ALL ANGLES’

In the meantime, South Portland officials are taking steps to evaluate the extent of winter moth damage across the city, develop a program to prevent tree deaths and enlist the public to join the fight. Winter moths prefer oak, maple, ash, elm and fruit trees and shrubs.

“We’re looking at attacking this from all angles,” said Karl Coughlin, deputy director of the city’s parks department. “We’ll be conducting a tree inventory in the coming months, but we’re really going to rely on the community to let us know where they see trees being affected.”

Coughlin met Tuesday with Cape Elizabeth Tree Warden Todd Robbins to learn what that town has done to combat winter moths.

Most trees can survive moderate winter moth infestations that destroy less than 50 percent of their foliage, says Cape Elizabeth Tree Warden Todd Robbins. Photo courtesy U.S. Forest Service

Cape Elizabeth has tripled its budget to care for trees in public parks and along roads – from $20,000 two years ago to $60,000 this year – because winter moth damage has exponentially increased the need for pest control, pruning, dead-tree removals and replacement plantings.

In recent weeks, volunteers helped Robbins band hundreds of tree trunks with sticky tape that captures the moths and is a key part of an integrated pest management plan.

Most trees can survive moderate winter moth infestations that destroy less than 50 percent of their foliage, Robbins said. If the moths do greater damage in the spring, a tree will immediately put out a second flush of leaves, diverting much-needed energy from the usual growth process.

Three or four years in a row with a second flush of leaves will kill a tree, Robbins said, especially under the recent drought conditions.

Winter moths are most visible now, between Thanksgiving and the start of the new year, when the insects emerge from the ground to mate when the temperature rises above freezing.

LESS COSTLY OPTION

While the male moths are most noticeable because they fly, the near-wingless female moths are the real culprits. They crawl up tree trunks and lay eggs that will hatch into larvae in the spring and gorge on new buds and leaves. Then the caterpillars drop and burrow into the ground, where they form cocoons and pupate from June through November.

Maine Forest Service entomologists Charleen Donahue and Colleen Teerling hold winter moth pupue infected with parasitoid flies. Maine Forest Service photo

That’s when the moths can be spread unknowingly by gardeners who swap plants from infested soil or sell them at fundraisers, and through mulch made from contaminated leaves, lawn clippings and other garden debris. They also can be transported by cars, boats and other vehicles that happen to be where the caterpillars fall.

Coughlin said he hopes to interrupt the spread by educating South Portland residents about the problem and promoting an integrated pest management program similar to the one in Cape Elizabeth.

Coughlin said he’s not sure how much it will cost, but he hopes residents help the city identify problem areas early. He’d rather spend the money on banding trees in the fall and applying horticultural oils in the spring that smother the caterpillars. If not, the city could face an even greater cost if it has to take down hundreds of dead trees.

“We know it’s here and it could get worse,” Coughlin said.

Anyone who sees winter moth activity is asked to report it to the Maine Forest Service at www.maine.gov/dacf/wintermothsurvey.

Kelley Bouchard can be contacted at 791-6328 or at:

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