State entomologists from the Maine Department of Agriculture, Conservation and Forestry’s (DACF) Bureau of Forestry will be releasing parasitic flies in an effort to try and control and minimize the damage to trees and shrubs done by the Winter Moth. The release is in collaboration with Dr. Joseph Elkinton, University of Massachusetts Professor of Entomology and the effort is funded by the United States Department of Agriculture’s Forest Service (USDA-FS).

Up to 2,000 parasitic flies (Cyzenis albicans) will be released, late morning, on Peaks Island May 15. Spring surveys of winter moth larvae indicate that Peaks Island has high enough levels of winter moth larvae to support release parasitic flies. Department professionals are checking to see if there are high enough levels of winter moth larvae to support additional releases at Two Lights State Park (Cape Elizabeth).

“The use of this biocontrol agent is part of a long-term approach to limiting the damage caused by the winter moth,” Maine Governor Paul R. LePage said. “Department entomologists are hard at work taking steps to protect our natural resource economy from invasive pests like the winter moth, which can also damage blueberry, apple and cranberry crops.”

Commissioner Walt Whitcomb highlighted the collaborative approach being taken between Maine, Massachusetts and the USDA-FS. “We thank USDA-FS, Dr. Elkington and the University of Massachusetts for collaborating with us on the timely release of these flies,” said Whitcomb.

A citizen supported winter moth survey and trapping by the Maine Forest Service in December indicated winter moth could be found from Kittery to Bar Harbor. Unlike some of the other invasive insects on our doorstep, this one has a potential biocontrol agent that can hopefully control the insects spread and limit future damage. Department entomologists and volunteers will monitor the winter moth and fly populations over the next several years to see how the release is working.

The winter moth is the latest invasive insect to attack Maine forests, with defoliation of oak, apple, birch, maple and other hardwood trees and shrubs. It made its first appearance in Harpswell in 2012 on 400 acres. In 2013, there were over 5,000 acres of defoliation, primarily in Harpswell and Cape Elizabeth. Last year saw a bit of a reprieve after a cold December that slowed the moth mating and egg laying, but almost 2,000 acres of heavy defoliation was mapped along the coast. Winter surveys have detected winter moth from Kittery to Mount Desert Island.

These flies were released in Nova Scotia in the 1960s, brought the winter moth population under control and there have been no adverse effects in the intervening 50 years. Flies were also released in British Columbia again with no impacts on other insects or people. The flies are very closely tied to the winter moth life cycle and need winter moth to survive. There will always be some winter moth around, now that they have become established in Maine, but hopefully the flies will do their job and bring the winter moth population under control in a few years.

It will take years before Maine will see the results of the biocontrol effort, as it takes time for the flies to become acclimated to a new location and build up their population. Once their numbers reach a high enough level, it will have a noticeable impact on the winter moth population. In the meantime people will see defoliation on hardwood trees and shrubs in May. It is hoped trees will not be too adversely effected before the parasite fly population catches up to the winter moth population and brings them into balance in Maine.

Featured photo: The winter moth. Photo Credit: Maine Department of Agriculture, Conservation and Forestry.