KINGSTON — For the first time in several years, Heather Faubert is not worrying about extensive winter moth damage. Faubert, a research assistant at the University of Rhode Island who advises commercial fruit growers on which pests to watch for and how to control them, said the winter moth’s decline began last year.
“I think very few acres were defoliated due to winter moth last year,” she said. “We had defoliation from other insects, but not from winter moth. The natural predators and parasites are building up that are kind of generalists that can feed on many different caterpillars.”
Winter moths, which are native to Europe and entered the United States from Nova Scotia, have been a problem in Rhode Island and Connecticut since 2004 and in Massachusetts since the 1990s. They spread by ballooning, in which the caterpillar drifts to a new location on a strand of silk. The moths are active in late fall, when they are often seen congregating around lights.
Winter moth eggs overwinter in the crevices of tree bark and hatch as leaf buds are opening. The caterpillars crawl up to the leaves and if they are opening, they enter and begin feeding. When moth-damaged leaves open completely, they have a ragged appearance.
Joseph Elkinton, professor of environmental conservation at the University of Massachusetts-Amherst, has studied winter moth populations at his laboratories in several locations in the state. He recently announced that this year’s winter moth numbers in Massachusetts were at a “record low.”
Part of the credit for the decline can go to a tiny parasitic fly, Cyzenis albicans, which Elkinton’s labs have released at 43 locations in Massachusetts, Rhode Island and Connecticut. It takes a few years for the fly to establish itself at a release site, but once it does, winter moth populations begin to decline.
Faubert and her team have been monitoring the eight Rhode Island release sites to determine whether the parasitic flies have established there.
“We collect caterpillars and then we check them for parasitism,” she said. “We collect a sample of about 500 caterpillars per release site, and then rear them and the pupae; we determine which are parasitized. And we’ve recovered the fly at three out of the eight release sites…Those locations were our first releases.”
One of Faubert’s most recent release sites is in Charlestown near the Richmond border, where flies were introduced in 2017.
In Connecticut, Kirby Stafford, who heads the Department of Entomology at the Connecticut Agricultural Experiment Station in New Haven, said extensive gypsy moth damage, which occurs in late April and May, has made it difficult to specifically assess winter moth defoliation, because it has been eclipsed by gypsy moths.
“There was defoliation observed and it’s still there in the southeast corner of the state, but the heavy gypsy moth defoliation wiped it out,” Stafford said.
He said his department was collaborating with Elkinton’s lab on parasitic fly releases, but he added that it would take a while to determine whether they are effective controls.
“We’ve worked with Joe Elkinton,” he said. “It takes several years. We’re looking at maybe in the next year or so.”
Faubert said that while the introduced parasitic flies seem to be promising controls, the winter moth decline is probably attributable to several factors, including native predators that were already established in the ecosystem.
“I hesitate to take credit for what we released,” she said. “It’s probably more the natural, generalist insects that feed on other insects. Because what has happened is, it seems like winter moths move into an area, the population of the insects builds very quickly, and after a couple of years of really high numbers, the population just comes down due to natural things building up.”