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Bad news for hardwood trees: There's a new caterpillar in Connecticut

Groton - A tiny lime green caterpillar crawled, accordion-style, on a deformed cherry tree leaf newly opened for spring, extending no bigger than an eyelash but leaving a telltale pattern of destruction far in excess of its size.

"You can see the holes in the leaves," Katherine Dugas, research assistant with the Connecticut Agricultural Experiment Station, said Tuesday, examining a low-hanging branch growing along the main path at the town-owned Beebe Pond Park. "Those holes were not eaten in a fully formed leaf; they were made as the leaf was forming."

As she continued along the path, she found the caterpillars at nearly every other hardwood along the way - red oaks, red maples, crab apples.

"They seem to be on everything I pick up," said Richard Conant, town of Groton committee chairman for the Avalonia Land Conservancy, which owns two adjacent properties, Town's End and Moore Woodlands. He had come to learn from Dugas about the invasive pest recently discovered at the town park.

Earlier this spring, Dugas was alerted to the winter moth presence at the park by Joseph Elkinton, entomology professor at the University of Massachusetts Amherst. He has been studying infestations of the winter moth, a European native that first appeared in Nova Scotia in the 1950s, as it has been creeping into forests in Massachusetts, Maine, Rhode Island and, most recently, Connecticut.

According to Elkinton, winter moths are spreading south and west at about 4.5 miles per year. Research published this spring by Elkinton and Kevin Dodds, U.S. Forest Service entomologist, describes how growth of red and black oaks at sites in Massachusetts has been cut in half by infestations of winter moths that defoliate trees and can ultimately kill them. The areas hardest hit by current infestations are in eastern Massachusetts, including Cape Cod.

Chris Martin, director of the Forestry Division of the state Department of Energy and Environmental Protection, said winter moths aren't widespread in Connecticut. Thus far they have been found only around here, in the southeastern corner.

"We're concerned. We're watching it closely," he said. "They infest the bud of the tree, which causes twig dieback. It's not as bad as the emerald ash borer or the Asian longhorned beetle, but the level of concern for this one is rising."

The first sign of an infestation, Martin said, is barren branches in the spring on a tree that should be fully leafed out.

"You'll see everything else green except for that tree. It'll look like late fall," he said.

A tree can survive a couple of years of infestations, experts say, but eventually it is killed when it is unable to produce new leaves repeatedly. "It's like missing a meal," Dugas said. "If it happens two to three years in a row, it saps the resources of that tree."

Earlier this spring, at the request of Elkinton, Dugas set out four traps for the caterpillars to confirm their presence at the park. Then last week, she released 1,000 cyzenis albicans flies as a biological control. After similar releases proved successful at curtailing the pest in Nova Scotia, the flies have been introduced to infested sites in Massachusetts and elsewhere.

Dugas said it would take several seasons for the flies to become established. In the meantime, she will continue monitoring Beebe Pond Park.

"When the fly gets established, it will be a policeman for this moth," she said. "It won't totally exterminate them."

The insects, she noted, are destructive to trees only in the caterpillar stage. As adult moths, they are active on mild days in mid-November through January, when they mate and lay eggs on twigs, tree trunks, lichen and elsewhere. In early spring, the eggs hatch and the caterpillars wriggle into tree buds to feed, then continue feeding on the leaves as the buds open. They attack a wide variety of hardwoods and other plants, including maples, oaks, ash, apple, blueberry, white elm and basswood.

The potential damage that can be caused if the winter moth infestation in Connecticut becomes severe, Dugas said, is equivalent to the scale of the destruction caused by the gypsy moth infestation in the Northeast that peaked in the 1980s, but has since receded after introduction of a fungus and other factors. She advised property owners who suspect an infestation to contact the experiment station or a licensed arborist before applying pesticides or taking other action. Doing nothing can be the most prudent response, she added.

"Sometimes nature takes care of it for you," she said.


More information

For more information about winter moths and other insects, call the Connecticut Agricultural Experiment Station's public inquiry office at (203) 974-8600. Information on winter moth can also be found at


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