Entomologists with the Maine Department of Agriculture, Conservation and Forestry are preparing for a sort of coming out party next week when 3,000 parasitic Cyzenis albicans flies are released in South Portland.
The flies have spent the winter buried and tucked into cocoon husks of the winter moth [Operophtera brumata] and once they take flight, the flies will be the front line offense in battling the destructive moth in Maine, according to Colleen Teerling, entomologist with the Maine Department of Agriculture, Conservation and Forestry.
“This is a form of biological control in the forests that is a true success story,” Teerling said. “The flies have been used to control the winter moth where they were real problems in Nova Scotia, British Columbia and Washington and now it’s to the point the winter moth is a non-issue in those places.”
The winter moth is an invasive species that showed up in the United States and Canada in the early to mid part of the last century. It came from Europe.
The winter moth caterpillars feed on the leaves of deciduous trees and shrubs such as oaks, maples, apples and blueberries, in early spring. Heavy defoliation for several consecutive years leads to branch dieback and tree mortality. Winter moth defoliation has contributed to tens of thousands of acres of oak mortality in Massachusetts and now there is oak mortality in Cape Elizabeth.
Winter moth defoliation was first recorded in Maine in 2012 and now the moths have been detected from Kittery to Mount Desert Island, according to Teerling.
Enter the parasitic albicans which enjoys a very specific relationship with the moth that is a sort of combination of “The Fly” and “Alien.”
Adult parasitic flies are attracted to oak leaves that have been damaged by the winter moths and the female flies will lay their eggs on those leaves, where they are then eaten by the winter moth caterpillar.
The fly eggs only hatch in the gut of the winter moth caterpillar, where they grow, pupate and feed on the caterpillar’s internal organs and body.
Eventually, the weakened caterpillar falls to the ground, dies and the fly uses the body as a home for the winter to mature, emerging the following spring to start the entire process all over again.
“It’s fascinating for entomologists to see this,” Teerling said. “It’s horrifying if you are a winter moth.”
Last fall Teerling and her crew obtained 3,000 cocoons from the University of Massachusetts which is leading a United States Department of Forestry-funded study of the fly-moth relationship and producing fly-filled cocoons for use by state agencies like Teerling’s.
“We will take as many cocoons as they will give us,” she said. “Last fall we put out a cage of 3,000 and buried it on the property of a citizen science volunteer in Portland [and] last week she let us know she has started to see some of the flies emerge.”
Those are the males, Teerling said, and the females should be emerging from their cocoons any day now.
“We are going to keep them in that cage for a few days to give them time to mate,” she said. “Then on Wednesday we will turn them loose and watch them head out into the trees.”
The parasitic flies are not dangerous to humans, birds or any other critter, Teerling said. In fact, if a bird or other animal eats one of the fly eggs, it will not hatch — it only hatches in the stomach of the winter moth caterpillar.
“The flies are only interested in winter moths,” she said. “The adult flies live around two weeks and spend most of their time buzzing around up in the trees.”
Teerling said the population of the parasitic flies and winter moths are carefully tracked in areas of the state where they have been released, including Cape Elizabeth, Vinalhaven, Portland, Kittery and Harpswell.
“We expect to see this working really well in controlling the moths in about 10 years,” she said. “That sounds like a long time, but in terms of biological controls it’s really fast.”
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