Extension Highlights

Cracking the Case of the Winter Moth

Bob Childs, Brenda Whited, Deborah Swanson and Joe Elkinton
Photo: Ian Churchill

Count on it, Deb Swanson is out there working her beat. Like a good cop, she keeps an eye on what's happening in her neighborhood, and when she sees signs of trouble, reports it. Then, if the people behind the desks aren't coming up with solutions, she comes back and tells them again—and then a few more times, if she has to. In the case of the winter moth, Swanson's tenacity was the driving force behind an important new discovery."I'm out there in the landscape 12 months a year, and I notice things," says Swanson, a Plymouth County Extension Educator. "Also, I'm a Type A person. As someone said about me: 'You don't say no to Deb Swanson.'" This persistence has proved crucial in solving the case of the winter moth, a pest she'd been seeing year after year stripping the buds from wide varieties of plants-shade trees, blueberries, rose bushes, even perennial flowers. Plymouth County was experiencing widespread defoliation.

Like good detective squads, Extension people work as a team. "We have a system," says UMass entomologist Bob Childs. "When pest problems come up, the extension specialists call me up and I identify the pest."Deb Swanson first sent Childs samples of this voracious insect in the early '90s, and Childs said, "I think we have fall cankerworm (Alsophila pometaria) here," which, he said, is a pest that should subside in the fourth year. But it didn't subside. "So Deb would call me and say, 'Bob, it's getting worse.' And then the next year, 'Bob, Bob, I'm telling you-it's getting worse!'" Childs proposed that it might alternatively be a spring canker worm (Paleacrita vernata), which would also be likely to subside spontaneously due to overpopulation and native predators. But, says Swanson, "I insisted that there was no moth flight in the spring, so it couldn't be the spring worm. It seemed as though this was something else, perhaps something new."Childs passed the problem along to his colleague Joe Elkinton, a forest insect ecologist, but he wasn't able to identify the insect definitively either, since it was now evident that the moths were emerging in winter, not spring or fall. They next sent their samples to David Wagner at the University of Connecticut, one of three top experts in North America on forest caterpillars. "He wasn't sure-which, frankly, made me feel better," says Childs. "But he thought it might possibly be the non-native winter moth." By the next year, 2003, the entomologists were pretty sure it was a non-native insect. Finally, "Richard Hobeke at Cornell verified that it was, in fact, a winter moth," says Childs.Adult winter moths, the light brown winged male and the gray, almost wingless female, emerge from the soil usually in late November. After mating, the females deposit eggs on the host plants' trunks and branches. Adult moths then die, and the eggs over-winter, turning from dark to orange to red just before hatching in March, just before bud break. The tiny (less than 1 mm) caterpillars, pale green with white stripes, spin a silk strand to become air-buoyant, and "balloon" upward into the tree canopy, where they crawl between flower and foliar bud scales, devouring them from within, then migrating to destroy other buds. At maturity of about an inch in length, they drop to the soil, where they pupate.

Winter Moths

Now that the insect had been identified and its life cycle described, the next step in the sleuthing process was to find out where it originated, in order to see if it had any natural predators. The scientists determined that the pest had made its way from Europe, where it is a problem in England and Scotland. It showed up several decades ago on both coasts of Canada, and had probably reached New England via Nova Scotia, where it has killed as much as 40 percent of the red oak population in places. And, yes, there is a natural predator, the parasitic fly Cyzenis albicans. Unfortunately, the scientists found no evidence of C. albicans in New England.

Now the effort is to keep the moth at bay until a good non-toxic control can be devised. UMass entomologist, Joe Elkinton has been raising C. albicans, parasitizing large numbers of caterpillars, with plans to release them this spring. Meanwhile Childs and Swanson are putting out advice to arborists and homeowners and horticulturists about temporary controls of the insect, which will surely be on our doorsteps if not in our backyards this spring. But because of excellent local detective work, at least we know who the enemy is.