Winter Moth Killer Safe for Environment and People

By TIM FAULKNER/ecoRI News staff

Those tiny holes in the leaves of your oak, maple and fruit trees are likely the work of the winter moth caterpillar, the same caterpillars that turn into moths and have swarmed porch lights in recent months.

The winter moth has been a problem in Rhode Island and the Northeast since at least 2004. State officials say the damage to leaves stresses trees, causing them to create more leaves. The stress makes them more susceptible to harm from other insects, drought and even lawn fertilizers.

To take action, the Rhode Island Department of Environmental Management (DEM) and the University of Rhode Island have introduced a parasitic fly that feeds on the moth. These flies lay eggs on tree leaves. The leaves and eggs are consumed by winter moth larvae. The flies then hatch in the winter moth cocoon and eat the moth during its pupa stage. The flies winter in the cocoon and hatch in the spring, when they start infesting winter moths all over again.

The tactic has worked in Nova Scotia, which was first invaded by the winter moth in the 1950s. The winter moth originates from Europe and has since been found in Maine, New Hampshire and Massachusetts. All three states have similar parasitic fly programs.

It’s expected to take about five years before the parasites run out of winter moths to devour and subsequently die off themselves, according to state officials.

Safe parasite
Bruce Payton, deputy chief of DEM’s Division of Forest Environment, said the parasitic fly, cyzenis albicans, is not a threat to people or the environment. A decade or more of trials in Nova Scotia hasn't shown any problems, he said.

“Nothing happened up there,” Payton said. There also has been extensive analysis locally. “You can’t just release stuff. There is a long, long (research) process,” he said.

Rhode Island has received grants of some $500,000 to pay for the past two years of using the parasitic fly. The results have been slow but effective, Payton said.

“I’d like them to see a lot more releases. But right now it’s a matter of funding and the economy,” he said.

Extensive tree damage occurs when maples, elms, ash, oak and beech trees are hit by the winter moth, followed by other pests such as the gypsy moth and the forest tent caterpillar. That’s what killed off about 100 acres of forest near Stratford Pond in Tiverton, according to DEM.

Another risk is damage to the fruit industry, such as growers of blueberries, cranberries, pears and apples.

“It an expensive little critter to raise,” Payton said of the parasitic flies. “It’s not cheap but well worth it if you consider the damage it can do to the industries like fruit and lumber.”

DEM has received reports of winter moths throughout Rhode Island, and particularly in the coastal communities of Warwick, Cranston, South Kingstown, Charlestown and Westerly. They have also been reported in Cumberland, Lincoln and East Providence.