Aliens and body snatchers

To stem the spread of invasive moths, UMaine entomologists turn to the species’ natural enemies
Photographs by Holland Haverkamp
The brown-tail moth was introduced into Northeastern North America from Europe in the late 1800s and rapidly spread through New England. Today, almost all of the North American brown-tail moth population is found in Maine.

Aliens and body snatchers

To stem the spread of invasive moths, UMaine entomologists turn to the species’ natural enemies

Photographs by Holland Haverkamp

High in the trees, as soon as the first leaf buds begin to open in the early spring, tiny brown-tail moth caterpillars emerge from their winter nests. The larvae feed voraciously on the young leaves, with a particular appetite for those from hardwood species, like apple and oak.

A heavily infested tree can contain more than 1,000 nests, each home to upward of 400 hungry caterpillars.

While large infestations can cause serious harm — or even mortality — to host trees, it’s the small toxic, barbed hairs on a caterpillar’s body that are of the utmost concern for public health, says Eleanor Groden, a professor of entomology at the University of Maine.

The tiny hairs can induce painful poison ivy-like rashes and serious respiratory distress in those who come in contact with them. The irritating urticating hairs often detach from the growing, molting caterpillars and become airborne, settling on line-drying clothing, backyard picnic tables, patio furniture and the ground beneath infested trees. The hairs can retain their toxicity for as long as three years.

Groden’s research focuses on understanding the brown-tail moth’s natural enemies — the various parasitoids, fungi and viruses that target the caterpillars — that may be used to help curb the rapidly expanding moth populations affecting Maine’s communities.

UMaine research is part of a larger initiative, working in collaboration with the Maine Forest Service, as well as a growing network of concerned citizen groups that monitor and identify new infestations, and develop pest management strategies in areas experiencing an outbreak.

The brown-tail moth, Euproctis chrysorrhoea, is an invasive species introduced into Northeastern North America from Europe in the late 1800s. At its height, before its populations collapsed in the 1920s and ’30s, the moth’s range reached from Long Island to Nova Scotia.

In subsequent decades, moth populations were largely isolated on the tip of Cape Cod and a few islands in Casco Bay. But beginning in the 1990s, small outbreaks of the insects began appearing on the mainland in midcoast Maine.

In the past several years, the population and range of the brown-tail have grown significantly. An outbreak in 2003 resulted in about 10,700 acres of defoliation, but then populations dropped until 2015. In fall 2015, populations started to shoot up, and about 12,000 acres were defoliated. By the following spring, this had increased to 24,000 acres and by fall 2016, 64,000 acres, Groden says.

Currently, almost all of the North American brown-tail moth population lives in Maine.

“We’re seeing an expansion of this insect that we haven’t seen in over 100 years,” Groden says.

The epicenter of the brown-tail epidemic has been focused largely around Merrymeeting Bay in the central and midcoast regions, says Groden. But new infestations are being identified statewide, and adult moths have been captured from southern Maine to Down East, as well as inland in Millinocket.

“I have a picture of a pupating brown-tail moth on a child’s stroller, so they get moved around inadvertently by people traveling through the infested areas,” says Groden. “It’s very possible that the infestations we have now in Burnham and Eddington may have resulted in pupae being moved into the area rather than moth flight.”

Adult brown-tail moths have pure white wings and bodies with a patch of contrasting dark brown fur at the rear of their abdomens — a defining feature which gives them their name. In late summer, a single female moth can lay as many as 400 eggs on the undersides of leaves.

Without preventative measures, outbreaks can spread quickly, and many people who live in areas not historically affected by the insect may be caught off guard, not knowing how to identify signs of an outbreak or how to take precautions against them.

According to Groden, the best time to spot a brown-tail infestation is in winter when their nests are most visible. In the fall, newly hatched caterpillars build tightly formed nests on the outer tips of branches and spend the winter inside, protected from the elements.

On particularly sunny winter days, the gossamer silk of the nests almost seems to glow high in the trees.

In the spring, the caterpillars emerge and begin to grow. Brown-tail caterpillars are easily identifiable — they are fuzzy and dark brown with white dashes along their sides. Two distinctive bright red dots punctuate the center of their back end. With each successive molt, their hairs become more and more toxic, reaching their highest potency in June, just before they build their pupal cocoons.

One of the most effective management strategies involves removing and destroying the web-like nests from infested trees during the winter before the larvae emerge.

Active community and state programs tasked with eliminating the nests on school grounds, and in public parks and people’s yards have been successful in slowing the population’s expansion in certain areas. In many other locations, the nests are situated high in trees and far from reach.

Another way to slow the epidemic is to harness the various parasitoids and pathogens that plague the insect.

“(Our research) is tasked with both looking at the natural enemies impacting the brown-tail moth and trying to understand under what conditions these natural enemies are having the greatest impact on the population,” Groden says.

Entomophaga aulicae, a fungus that infects the brown-tail, is one of these natural adversaries. The disease it causes in the caterpillars can decimate regional populations. However, the success of a disease outbreak, or epizootic, is largely dependant on uncontrollable seasonal and environmental variables, including temperature or amount of precipitation during the phases of larval development.

The study of this complex relationship in organisms is called phenology. Small variations in seasonal timing and weather — if spring is early or late, warm and dry, or cold and wet — can greatly influence when development phases occur, including when caterpillars leave their nests to feed, and when they begin to pupate or lay their eggs.

For example, during a cold and rainy period in May 2017, the fungus took hold in some of the state’s brown-tail population. Wet conditions allowed the naturally occurring fungus to proliferate, infecting the feeding young caterpillars that, due to the cold snap, had temporarily retreated to the protection of their winter nests.

“There is still so much we don’t know so much about (the brown-tail) even though it’s popping up in everyone’s backyard.” Karla Boyd

In the tightly packed webs, the disease ran rampant, resulting in a mass die-off. However, the impact was highly localized. Despite the collapse of brown-tail populations in some areas, other areas were not similarly affected.

Had the spring been drier, the fungus may never have spread. Alternatively, had the temperature been higher, the population of young caterpillars may have been too dispersed for the disease to spread quickly, limiting the mortality rate.

Had the fungus taken hold later that spring, or even in early summer, the infected caterpillars would have been further along in their larval development with toxic hairs at their most potent.

A mass die-off during this stage could result in thousands of dead brown-tail caterpillars raining from the high trees onto yards, parks, playgrounds, cars and houses — losing their urticating hairs to the breeze — and putting people in the area at risk for years.

This underscores the delicate balance between the slight year-to-year variations in seasonal weather, and the timing of key biological events of the brown-tail and its enemies’ life cycles. It’s also why manually distributing the fungus and other pathogens, even pesticides, as a means of pest management presents a tremendous challenge.

Understanding how these complex phenological interactions either stack the deck for or against the brown-tail is critical in effectively developing and using these methods of population control.

In Groden’s lab, glass jars and stacks of petri dishes containing brown-tail caterpillars from throughout the state are organized beneath a ventilation hood designed to limit harmful exposure to toxic fumes, vapors or, in this case, airborne caterpillar hairs.

Cloaked in a long white lab coat with rubber gloves taped over the cuffs, graduate student Karla Boyd inspects caterpillars for signs they have fallen prey to parasitoid wasps and flies.

Some native species of wasps and flies inject their eggs inside live brown-tail moth caterpillars. When they hatch, the larvae eat the host caterpillar from the inside out before using the carcass to pupate.

Boyd’s graduate research largely is focused on trying to find ways to exploit this natural adaptation to help stem the expanding moth population. It’s also important that the natural means of control are the least detrimental to other species, Boyd says.

Without preventative measures, outbreaks can spread quickly, and many people who live in areas not historically affected by the insect may be caught off guard, not knowing how to identify signs of an outbreak or how to take precautions against them.

“There is still so much we don’t know so much about (the brown-tail) even though it’s popping up in everyone’s backyard,” says Boyd.

In the course of her research, she has become painfully aware of the rashes the caterpillars cause. Despite the protective measures in the lab and the full-body Tyvek coveralls the researchers wear in the field, the occasional rash is par for the course. And, according to Boyd’s firsthand experience, with each successive exposure to the toxin, the more severe the reactions can become.

The painful consequences of interacting with the brown-tail, as well as its highly localized population range, have historically made the study of the species difficult. As a result, very little concerted research on the insect has been done; the brown-tail moth and effective pest management strategies remain enigmatic.

“One of the things about this insect that makes it challenging to develop a research program is that right now, it’s not impacting anyone outside of the state of Maine. That makes it more challenging to get the resources to work on this project,” says Groden. “But because members of the community are willing and motivated to help in our project, it has helped us be able to address some of the issues with our research.”

Charlene Donahue, a forest entomologist with the Maine Forest Service Insect and Disease Laboratory, works closely with Groden. Her office supports the UMaine research by sharing samples and providing access to locations and site monitoring, as well as occasional funding.

She also organizes outreach and educational events, and helps to implement new management strategies bringing new findings straight to the affected communities.

“The Maine Forest Service is so happy to have (Groden) and her students perform the research on forest pests that we simply cannot do; we don’t have the people or the time,” says Donahue, who received her bachelor’s and master’s degrees from UMaine in 1975 and 1982, respectively.

“It’s a huge benefit to the state of Maine.”

Over the winter, the Maine Forest Service conducted its annual survey of webs to gauge the size and extent of the overwintering brown-tail population.

Though the numbers are forecast to be lower than 2017 in some areas in the center of the outbreak region, 2018 winter web surveys indicate the outbreak region is expanding. Many communities will continue to be affected by the brown-tail menace, and new areas will begin to experience the effects of the irritating insect for the first time.

The brown-tail isn’t the only invasive moth Groden, her students and the Maine Forest Service are keeping tabs on. According on Donahue, Maine is now home to at least four other invasive moth species: gypsy, winter, ermine and leek. The ermine and leek moths were first identified in 2017.

The winter moth began spreading into the southern part of the state in 2011. While winter moth caterpillars forgo the toxic hair of their cousins, infestations of the larvae can wreak havoc on the state’s leafy hardwood trees. They will even eat blueberry bushes clean of their leaves. And like the brown-tail, the winter moth has its own share of parasitoids.

According to the Maine Forest Service, areas in Bowdoinham and Topsham were particularly hard hit by the brown-tail in 2016. The issue prompted local residents to form the Bowdoinham Browntail Moth Task Force. Its mission is to educate homeowners and community members about the brown-tail, as well as effective ways to mitigate the population. The task force works closely with members of the Maine Forest Service and UMaine researchers.

Kate Cutko directs the Bowdoinham Public Library, which provides information and equipment to combat brown-tail moth infestations in the hard-hit community.

Groden, Donahue and Kate Cutko, the library director of the Bowdoinham Public Library, are task force members.

“When we learned that people could clip the winter nests out of the low trees in their yard, the library went ahead and purchased a 16-foot pole pruner that could be borrowed by patrons,” Cutko says.

The task force also produced a short video about clipping the winter nests, and it hosts regional informational meetings at the library. And it created Midcoast Maine Browntail Moth Support, a social media group that disseminates information statewide about the insect.

“To be able to have (Groden) and (Donahue) on speed dial is a gift,” says Cutko. (Groden) is one of the few people studying this problem, and her research is vital to giving people hope that we will see the cycle; we will get to the other side of our daily life in Bowdoinham.”

Groden says that many residents are supporting and facilitating her research — from sending her pictures of brown-tail activity to providing her access to infested trees.

“The interest and willingness of landowners to support this project is what has enabled us to conduct our sampling program and help us identify areas we can monitor,” says Groden.

“Like all good public libraries, we spread information,” says Cutko. “And when we’re lucky enough to have University of Maine scientists feeding us the latest information, it’s a great collaboration.”

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