Local trees could be in for another beating

Emergence of winter moths worries researcher

Todd McLeish

They’re back. Winter moths should be fluttering around porch lights and car headlights any day now, creating a nuisance and laying eggs that may lead to another spring of defoliated and dying trees.

That’s the warning from Heather Faubert, who runs the Plant Protection Clinic at the University of Rhode Island. She said the adult moths – an invasive species native to Europe – begin emerging from the ground around Thanksgiving and die before the New Year.

“I’ll be very curious to see what happens this year,” said Faubert, who monitors the population of the insects each year. “Their caterpillars defoliated 27,000 acres in Rhode Island in the spring of 2015, but even though we had winter moths everywhere last year and I saw a zillion eggs, they caused almost zero defoliation.”

Last year’s state-wide defoliation, which began after winter moth caterpillars had long become inactive, was caused primarily by gypsy moths and, in some communities, forest tent caterpillars.

Faubert believes last year’s strange winter and spring weather negated what she expected to be a dire season for winter moth defoliation. 

Winter moth eggs typically hatch during a warm spell in April, but last year they began hatching during a warm period in late March. Two weeks later, in early April, temperatures dropped well below freezing and probably killed many of the caterpillars.

“I went looking for dead caterpillars but didn’t find many,” she said. 

“Maybe the caterpillars hatched too far ahead of the foliage development, so they didn’t have anything to eat. I’m not sure what really happened, but it definitely had something to do with our screwy weather.”

With little defoliation occurring last year from winter moths, Faubert said it’s possible that there will be fewer adult moths flying around in the next month. But that doesn’t mean Rhode Islanders should expect little impact from the insects.

“Each individual female can lay hundreds of eggs, so it could still be a bad year for defoliation in the spring,” she said.

What’s worse, according to Faubert, is that the combination of several years of defoliation in a row and the extended drought conditions could mean that more trees will die in the coming year.

“Defoliation is very stressful to trees,” Faubert said. “That alone can kill trees. But having drought conditions is the worst thing that can happen to a stressed tree.”

What can homeowners do this winter to combat the effects of winter moth caterpillars? Not much. Faubert said that attempting to kill the flying moths is useless since only the males fly. The females crawl up tree trunks to lay their eggs.

“Lots of people try using those adhesive tree bands, but the moths will just lay their eggs right below the band, and many of them can make it across the bands,” she said.

In an experiment she conducted last year, Faubert placed two tree bands, separated by about a foot, around one tree. The first band caught 207 female winter moths, while the second one caught 138. It is unknown how many made it past both bands.

One strategy Faubert is deploying to control winter moth populations is the release of a tiny parasitic fly that lays its eggs on tree leaves. When the winter moth caterpillar consumes the eggs while eating the leaves, the eggs hatch inside the caterpillar and the fly larva eat it from the inside out. The fly has succeeded in controlling winter moth populations in Wellesley, Mass., and it appears to be on its way to doing so in Seekonk as well.

Faubert released the flies in seven locations in Rhode Island between 2011 and 2015, and she hopes to soon see signs that it is beginning to work.

“It’s still too early to tell, but we hope the flies will get our moth population down to manageable levels,” she said.