Each spring, University of Massachusetts Amherst researchers do something strange: They go out and shake trees — sometimes for hours at a time — to collect caterpillars.
“We hit the trees and caterpillars come raining down,” said Joseph Elkinton, a UMass Amherst professor of entomology, the study of insects.
Led by Elkinton, the team has been measuring the impact of its effort to use flies to control winter moths, an invasive species with an unknown origin and an appetite for trees. They eat away at leaves and buds on oak, maple, and ash trees, along with fruit trees.
Winter moths started munching on Massachusetts’ trees in the late 1990s. The species has since expanded its range from north and south of Boston to mainly coastal areas of Rhode Island, Maine, southeastern Connecticut, New Hampshire and Long Island, according to Elkinton’s research. True to their name, the insects fly in late November into December. The creatures have done particular damage to blueberry bushes and cost eastern Massachusetts farms their crops, according to Elkinton. “It was a tough problem,” he said.
Since 2005, Elkinton and his team have released over 80,000 flies in 44 spots spreading over parts of New England. The species of fly, Cyzenis albicans, is a parasite that can kill the moths. And it seems to be working — the population has been reduced by at least tenfold, Elkinton said.
The team isn’t the first to use the flies to control winter moths. In the 1950s, an outbreak of winter moths in Nova Scotia was successfully brought under control using the same fly species, Elkinton explained.
The process is a laborious one. Hannah Broadley, who worked on the project with Elkinton while completing her Ph.D., said that flies are released in the spring and lay their eggs.
“Caterpillars then inadvertently eat the eggs while they are eating the foliage,” Broadley said.
When those caterpillars reach their pupa stage, the stage before becoming a full-fledged moth, the parasite takes control. “In essence, the caterpillar has been eaten from the inside out,” she said.
To figure out how effective the flies have been, Broadley said, the team typically collects hundreds of caterpillars from each site — that’s where the tree-shaking comes in. Then they wait for them to reach the pupa stage where they can tell under a microscope if they have been infected.
“It’s a logistical challenge to do this project,” Elkinton said. They usually release 1,500 flies at a location, and the process of caterpillars collecting at all those sites can require dozens of people.
The business of introducing a new species to control another, or “biological control,” is not one that that’s always gone right, as with the infamous example of the cane toad. The toxic amphibian was introduced in Australia in 1935 to take out beetles eating sugarcane, but instead of fixing the bug problem, the species become a new issue when its population boomed and spread.
“We’re much more careful than we used to be,” said Elkinton of the technique. He said the team went through a USDA permitting system before releasing the flies, plus make sure that the flies wouldn’t attack natural species. In this case, Elkinton said a Canadian team had already done testing that showed it wouldn’t inadvertently hurt other species. The researchers also had previous successful examples of the fly approach, like the one in Nova Scotia.
Valley residents are not under an immediate threat though — the winter moths have not descended upon western Massachusetts. They’ve been spotted as far west as Athol, but the moths mostly stick to coastal areas. “We think something about the interior is too harsh,” Elkinton said. If a resident does happen to find an outbreak of green caterpillars in late May though, “They should let me know,” he said. Elkinton and his team would want to check it out.
Still a mystery is where the moths came from in the first place. Elkinton said researchers are currently analyzing a world wide winter moth collection of DNA and comparing it to the genetic makeup of the one found in Massachusetts. But, it’s really an academic exercise. “I don’t know if we will ever know where it came from,” Elkinton said.
A variety of papers and other materials have been written on the topic. Recently, Elkinton and Broadley were co-authors on a pamphlet with the U.S. Forest Service. Up next, several papers are in the works on the research. “We have a whole suite of papers to write,” Elkinton said.
The invasive species is not totally gone though and Elkinton said it will never be. But the point is to greatly reduce its numbers, and that’s what it appears they’ve done. Broadley said the population has been reduced to a non-pest level.
Pointing to moth and fly specimens in a dish in his lab, the moth dwarfs the fly. “A small insect can do a big thing,” he said.
Greta Jochem can be reached at firstname.lastname@example.org.