Browntail Moth Looms Again in Northeast

The browntail moth larvae is the damaging stage for both trees and people. Source: Maine Forest Service

According to the Maine Forest Service, it’s one of the worst major, widespread outbreaks in over one hundred years.

The villain: browntail moth, first introduced to the northeastern United States outside Boston in late 1800s. It quickly spread as far as Nova Scotia and Long Island, and westward through most of New England. The century-old eruption occurred at about the same time as the gypsy moth invasion. Then, collectively, we released about 60 to 70 different biocontrol agents for both moths.

The program was a success, or perhaps it was a coincidence. In the 1920s, populations of browntail moth declined. In the 1940s and 50s, small relic populations of browntail moth persisted on islands off the coast of Maine and on the outer tip of Cape Cod.

Back in the early 1990s, small flare-ups occurred on islands and at a couple of localized sites on the coast of Maine. These hotspots meant a couple of thousand acres infested.

Then, in the early- to mid-2000s, the moth infested a few thousand acres. In 2015, the onslaught suddenly spread, from 24,000 acres to 64,000 acres.

A Health Threat, and Worse

In mid-coast Maine, the moth brought severe defoliation to oak, apple, and cherry hardwoods, and a wide range of other host trees.

The main threat with this insect: Caterpillars, starting after the third molt, have what scientists call urticating hairs that have a toxin in them.

These hairs break off the caterpillars when they molt and shed skins. These hairs can become airborne. A survey that was done on one of these infested islands in the late 90s found that about 84 percent of the people in the infested area get a severe rash from these toxic hairs and 21 percent experience respiratory problems.¹

“So you have a big problem of defoliation,” said Eleanor Groden, an entomologist at the University of Maine, “plus serious health concerns in infested areas.”

The epicenter for the infestation happens to be a particularly productive agricultural area for Maine, north of Portland: vibrant vegetable farms and pick-your-own fruit. Many of these farms are surrounded by infested trees. The moths may in fact infest commercial tree fruit crops.

“Browntail moth prefers apple, crab apple, cherry and oak,” said Groden. “Because they can defoliate trees twice per season, they can cause considerable stress to trees if not managed.”

Browntail moth adult. Source: Maine Forest Service

People can survey for the browntail moth overwintering web stage, to monitor for the upcoming population. Source: Maine Forest Service

Nuisance to Growers

Farm workers, family members, and customers could be exposed to the caterpillars when they seek shade in the field borders or mow.

“One grower who contacted us to express support for our work is an organic farmer who has their farm stand right under infested oaks,” said Groden. “It has been a serious problem for them.”

Since this insect hasn’t been too serious a problem in over one hundred years, there haven’t been a lot of up-to-date pest management recommendations.

Groden and her colleague, Charlene Donahue, entomologist with the Maine Forest Service, are working on a project focused on targeting the insect before it starts its equivalent of hibernation. The browntail moth caterpillars overwinter in the third and fourth instar, or stage of development, in webs in the tops of trees. In the spring, as the buds break, the insects start to feed on the foliage. That’s when they are particularly hazardous to people, when they develop into the larger larvae that have toxins in their hairs. The caterpillars pupate in July and new adults emerge in late July or early August, and lay their eggs. Small larvae hatch in late August and begin their defoliation of trees, which continues into early September when they begin their hibernation.

Groden and Donahue are leading a project sponsored by the Northeastern Integrated Pest Management Center at Cornell University, focusing on treatment options for early August, targeting newly hatched larvae. The goal is to disrupt the reproductive cycle of the moth at what may be its most susceptible stage.

Looking Ahead

“This is a tremendously important project for the northeast region,” said Groden. “We do not know how far the outbreak will spread and how long it will continue. Given that the distribution of browntail moth during its last widespread outbreak one hundred years ago extended across the Northeast and into Canada, it warrants monitoring and developing up-to-date management strategies for impacted areas and crops.”

“The browntail moth infestation is occurring in the same area as an infestation of the invasive winter moth,” said Donahue. “So there is concern for the health of the trees when multiple stressors hit the same trees. Even more important is the impact on people in what is for Maine one of the most densely populated areas. Hopefully this research will bring answers to protect people and trees from browntail moth.”

And with a little science, hopefully the browntail moth will no longer be a significant threat to the economy and health of the Northeast.

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