AUGUSTA — While browntail moth caterpillars are hibernating in their nests, Eben Mann’s appointment schedule is starting to fill up.

A year ago, Mann, owner of Mann’s Lumber & Tree, was debuting a new service for clients who were searching for ways to clear their properties of the invasive pest by using a cutting tool mounted on a drone to clip hard-to-reach caterpillar winter nests from the tops of trees.

The year 2022 was predicted to be the worst year of the current browntail moth outbreak in Maine, and the most severe impact was expected to be in Kennebec County. The pressure was on to do whatever possible to eradicate the insect before it reached another breeding stage.

This year, Mann said, he’s starting to see some repeat business as people start to assess the number of browntail moth nests they see in their yards.

“I think we could have just as much potential for a big outburst this coming summer,” Mann said recently.

Even so, the expected 2022 browntail moth population boom in central Maine kind of went bust.

Tom Schmeelk, an entomologist with the Maine Forest Service, said the reason is that many caterpillars fell victim to pathogens that shrank their populations.

That shift was due to some periods of cool, rainy weather in May and June that promoted the spread of a fungus that is fatal to the caterpillars. During the very dry springs of 2020 and 2021, that fungus wasn’t able to spread, and the browntail moth caterpillar populations exploded as a result.

The evidence is found in the aerial survey data that’s collected twice a year, once in late spring or early summer to measure defoliation by the large caterpillars, and once in the late summer or early fall to measure leaf damage from the newly hatched caterpillars.

“In 2021, we had about 200,000 acres of defoliation, but this past summer we only picked up 152,000 acres roughly,” he said. “So that denotes a decrease of about 47,000 acres.”

The greatest population collapse was in Kennebec County and surrounding areas, he said, and that’s why the adult moths were not seen in great numbers during July, when moths typically emerge from their cocoons, mate and lay eggs.

“That being said, there are three counties that are experiencing a population increase,” he said. “Androscoggin County, particularly in the Turner-Leeds area; Penobscot County, which is experiencing a large population boom; and then Waldo County, which has been hard hit for a number of years and also still has a very high population.”

NEW DEVELOPMENTS

Schmeelk said that means that outbreak will continue, and that’s going to drive more eradication efforts.

For more than a century, people have been battling the invasive pest. The moth, native to Europe and western Asia, was introduced in Massachusetts in the late 1800s. Eventually, it spread along the northeast coast. In Maine, it had been confined to coastal areas but since 2015 the population has boomed and it’s now found across the state.

Aside from the damage browntail moth caterpillars do to hardwood trees and shrubs like oaks, maples and fruit trees, they are also a threat to human health. In the caterpillar stage, they shed toxic hairs that cause skin rashes and respiratory problems in people who are sensitive to them. Symptoms can last from a few hours to several weeks.

Human-assisted disease dispersal was one of the methods used more than a century ago to control the spread of browntail moth caterpillars. Schmeelk said entomologists had wondered how that had worked and they set out to find out.

Last year, entomologists secured funding from the U.S. Forest Service’s Emerging Pests grant program to pay part of the cost of trying a form of natural control via a baculovirus and a fungus that are fatal to the caterpillars.

During the summer of 2021, Schmeelk collected dead caterpillars and stored them in a refrigerator in the lab over the winter. Last spring, he brought the caterpillars to three test sites in the state, in Chelsea, Deer Isle and Cumberland, and exposed live caterpillars to them.

“I put them in a cup and shook it up a bit so they got some fungal spores or some virus on them,” he said, “and then I would take them and put them back on the foliage.”

The three sites were monitored over time, and evidence showed the inoculation was a success. The pathogens had done their work and controlled the caterpillar population.

While showing the feasibility of the method was one of the goals of the grant, Schmeelk said, scaling it up for a broader application poses some challenges, including collecting a lot of dead caterpillars or rearing them in a lab, which is difficult to do.

“At this point, we don’t really have the infrastructure to, or the capability to, implement it at scale,” he said.

NEW TECHNOLOGY

When Mann debuted his drone-based trimming service, he and his staff had not flown drones and were not that familiar with the technology. It requires two people, one to pilot the drone and the other to use a hand-held video screen to direct the drone to the nest and operate the cutting tool.

But over the course of the spring, they became more skillful at the process. In December, he said, his team returned to a project it had done earlier in the year and was able to do nearly four times as much in the same amount of time.

While other services have used pesticides to help control browntail moth caterpillars, he said he has opted not to do that. Like other arborists, he used to climb trees to access nests, but he found it’s not worth it to him.

In addition to operating the drone system, Mann is also selling the systems, and to date, he said he’s sold three, including one in the Augusta area.

Even as people are advised to continue to find and destroy browntail moth caterpillar nests, some help is on the way for municipalities and nonprofit organizations.

The state of Maine has created the Browntail Moth Mitigation Fund, setting aside $150,000 to support efforts to knock down the pest in eligible areas of the state with significant browntail moth populations. Money distributed through the program can be used for removing and destroying webs, pesticide treatments, making habitats less friendly and education, among other things.

A public hearing on the rules to run the program was held on the program in November 2022 and comments on the program were collected through Dec. 2. The rules are now under review at the state Office of the Attorney General.

The Maine Forest Service also has a list of resources on its browntail moth web page that the state will start promoting again in February, which is Browntail Moth Awareness Month in Maine. The site includes maps, lists of pesticide applicators and arborists and information on how to identify browntail moth caterpillar winter nests and how to tell the difference between them and the nests of beneficial insects.

CONTINUING VIGILANCE

Schmeelk said even though the number of acres affected in Kennebec County has decreased, the threat from the pest has not ended.

“To give you an idea, last year we had 152,000 acres of defoliation mapped,” he said. “In the last outbreak in the early 2000s, it was around 6,000, 7,000, 8,000 (acres).”

Both Schmeelk and Mann say they have seen plenty of nests as they drive around the state, and each nest holds the potential to extend and spread this outbreak.

Each nest that survives the winter has in it anywhere from 25 to 4o0 caterpillars, so clipping and destroying as many as possible is recommended, he said. After clipping, they can be burned or soaked for several days in soapy water and discarded.

Schmeelk said that when he can, he tries to stop and knock on people’s doors to let them know they have nests and what to do about them.

“Just go out on a sunny day and check your trees,” he said. “Stand with the sun behind the nests, they kind of shine in the sunlight.”

As Mann was wrapping up some year-end jobs in December, he said he has a list of people who asked to be contacted this year for nest eradication, but he doesn’t have to look to hard to see signs of the ongoing infestation.

“In my area of travel,” he said, “there’s just as many nests as there was this time last year.”

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