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The winter moth, an invasive species that chewed through New England shade trees and blueberry bushes for years, is no longer a threat, say entomologists at the University of Massachusetts Amherst.

The researchers reported “major progress” in their fight against the European moth species in a statement Wednesday after finding that a parasitic fly species called Cyzenis albicans was able to establish itself and control the winter moth population in 38 of 44 coastal New England sites where it was introduced.

“After 14 years of effort, we have successfully converted winter moth, a major new defoliator invading eastern New England, into a non-pest, presumably on a permanent basis,” entomologist Joseph Elkinton said, according to the statement.

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A parasitic fly species, Cyzenis albicans, established itself and controlled the winter moth population in 38 of the 44 coastal New England sites by feeding on the moths.
A parasitic fly species, Cyzenis albicans, established itself and controlled the winter moth population in 38 of the 44 coastal New England sites by feeding on the moths.(Robert D. Childs/University of Massachusetts Amherst)

Managing the moth population was accomplished with a technique called biological control. Cyzenis appears to be an absolute specialist, meaning its sole source of food is the winter moth. After learning that the fly species had reduced winter moth populations in Nova Scotia and British Columbia, the team raised flies in a UMass lab and introduced them to a few dozen coastal New England sites in spring 2005. By last July, the fly species had been established in 44 locations.

“The object of biological control is to reduce density of the invasive species to non-pest status,” Elkinton said in the statement. “That is what we believe we have achieved.”

Once the fly species is established in an area with winter moths, the researchers found, the populations of both species drop within a few years, so even though the flies have abundant food, they do not become a pest themselves.

The moths cannot survive the colder winters of inland areas. The researchers recommend that coastal New England residents who see the moth (or the caterpillar when it is younger) do not kill it. Instead, they suggest letting the flies reduce the moth population on their own.

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The spread of moths caused “wide-spread defoliation of coastal New England shade trees and blueberries.”


Andres Picon can be reached at andres.picon@globe.com.