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Vanquishing the Winter Moth

UMass scientists halt a major threat to New England’s trees and crops.

Illustrations by Patrick Hruby

In the late 1990s, Operophtera brumata—the winter moth—invaded New England. The small brown moth is native to Europe. Male winter moths fly in December, giving them their name. The wingless females lay their eggs on bark or in crevices on the stems of trees. 

When the eggs hatch in spring the voracious green inchworms feed on the swelling buds and leaves of their host trees, resulting in defoliation.

By 2005, the winter moth was spreading fast. In parts of eastern New England, trillions of winter moths wreaked havoc on oak, maple, birch, and apple trees—and many blueberry bushes, wiping out entire crops. It looked as if the winter moth could become as big a pest as the dreaded gypsy moth.

Bring on biological control! Entomologist Joseph Elkinton and colleagues at UMass Amherst deployed a parasitic fly, Cyzenis albicans, to combat the winter moth. The UMass scientists collected C. albicans from Vancouver Island in Canada and, beginning in 2005, released them at several sites each year for a total of 44 sites around eastern New England where winter moth outbreaks occurred.

Winter moth caterpillars eat the eggs of C. albicans. The egg hatches and the fly larva devours the caterpillar from the inside out and then forms a pupa inside the winter moth pupa, killing it. The fly attacks
no other species.

By 2018, UMass scientists had released 80,000 flies and had established C. albicans at 38 sites. The winter moth population has declined sharply—without the use of pesticides. New England’s native forests, backyard trees, agricultural lands, and sensitive ecosystems are now free from the threat of the winter moth. The work of UMass Amherst has averted a major invasion calamity. A small insect can do a big thing.

Joseph S. Elkinton, professor of entomology in the UMass Amherst Department of Environmental Conservation, worked with UMass entomologist George H. Boettner and UMass postdoctoral researcher Hannah J. Broadley ’16G, ’18PhD, along with Richard Reardon and Ronald D. Weeks Jr. of the USDA on biological control of the winter moth. The work was funded by the Commonwealth of Massachusetts, the U.S. Forest Service, and the USDA’s Animal and Plant Health Inspection Service (APHIS).