Researchers: Rain will curb next year's gypsy moth population

By Angie Hilsman | Jul 05, 2017

A female gypsy moth lays about 600 eggs at a time, resulting in an influx of caterpillars around early May, when they generally hatch.

While heavy rainfalls typically curb the insect's population, this year's rains have only delayed the gypsy moth boom, researchers said. The rainfall won't drastically affect populations until next year, they said.

"Down in our neck of the woods, they don't seem to be too bad. But in North Dartmouth, they're everywhere," said the Lloyd Center's Research Director Mark Mello.

He explained that drought conditions — like that of 2014, 2015, and 2016 — surge gypsy moth numbers, while rain reverses the trend because it encourages the growth of entomophaga maimaiga, a fungus that kills the caterpillars.

"The fungal spores penetrate the caterpillar's skin and multiplies," explained University of Massachusetts Amherst entomology professor Joseph Elkinton. "You'll see thousands of dead caterpillars around the base of trees."

However, because of its cooler temperatures, the caterpillars develop more slowly along the South Coast, Elkinton said. As conditions dry out, more caterpillars survive.

In a typical season, gypsy moth larvae molt several times, then pupate toward the end of June. They emerge two weeks later as adult moths. The mating season continues until late July or early August.

Alongside hanging from trees, the hordes leave their mark through defoliation.

"They eat the leaves, oak trees especially. It looks like winter," said Elkinton. He said that around his own residency in western Massachusetts, the gypsy moths are much worse than last year.

But Mello is hopeful for Dartmouth. "Some areas will escape total defoliation," he said. "They'll be here at some level [next year], just not at the level we've seen in the last couple of years."

Mello recommended inspecting trees for signs of gypsy moth egg masses during the fall and winter and removing them.

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