02-06-2025
Maine tree spraying will kill any caterpillars, not just forest pest
Jun. 2—A government-funded campaign has begun spraying insecticides and biological agents on 240,000 acres of Maine's North Woods infested with spruce budworm, a voracious forest pest that killed millions of spruce and fir trees during its last population explosion.
JBI Helicopters began spraying tebufenozide over 9,000 acres in far western Maine on Thursday, said spokesman Jim Britt of the Maine Department of Agriculture, Conservation and Forestry. The spraying, approved by the Board of Pesticide Control in April, could last through June 25 of this year.
The tebufenozide, which is sold under the brand name MIMIC, kills the budworm caterpillar by triggering a premature molt. A biological agent, Bacillus thuringiensis kurstaki, or Btk, is also authorized for use, but will likely be applied in much smaller amounts. It destroys the caterpillar's gut lining.
When applied properly, neither agent will harm people or most animals, according to Doug Van Hoewyk, a state toxicologist with pesticide board. Any caterpillar that eats it will die, however, including those that turn into beneficial moths and butterflies.
Several beneficial moths and two state-threatened butterflies live in or near the targeted spraying area.
Clayton's copper lays its eggs and collects nectar in shrubby cinquefoil stands in bogs, fens and streamside meadows, including some near New Sweden. The Arctic fritillary feeds and lays its eggs on dwarf willows in the mature coniferous forests of Big Twenty Township, Maine's northernmost community.
"Maine has an important role in conserving the rare Clayton's copper butterfly," according to the species description posted by the Maine Department of Inland Fisheries and Wildlife. "This small metallic purple and bronze jewel is found only in Maine and just over the border in New Brunswick."
The state agency identifies several threats to the species: floods that destroy the copper's eggs, larvae and host cinquefoil stands, forest succession that creates too much shade for the sun-loving cinquefoil to tolerate, and aerial insecticide spraying.
A study published in Science in March found about one in five U.S. butterflies, or 22%, have disappeared over the last 20 years. Clayton's Copper and Arctic Fritillary were too rare to be included in the study, but seven of Maine's other 118 species showed some of the country's fastest declines.
In its chapter on butterfly conservation, the authors of a 2023 field guide, "Butterflies of Maine and and the Canadian Maritime Provinces," warn that widespread budworm spraying has the potential to reduce butterfly abundance at both the population and landscape level.
The early intervention strategy that Maine is using to spray on the leading edge of the outbreak will limit the geographic scope of the spraying, the authors say, but it "does not eliminate the threat of incidental spray impacts to butterflies." One of those authors leads the state's wildlife diversity division.
To protect these rare butterflies, JBI must not spray within a quarter-mile of habitat these species are likely to frequent. The quarter-mile buffer is recommended by the biological agent manufacturer and was written into the Maine Board of Pesticide Control's spray permit.
The Maine Department of Inland Fisheries and Wildlife "anticipates minimal impacts to these two species as a result of project activities," senior resource biologist Andrew Wood told Ked Coffin of Irving Woodlands, a leader of the Maine Budworm Response Coalition, in an April 20 letter.
At a public forum on spruce budworm earlier this month, state wildlife biologists and pesticide regulators said Maine's solution to its budworm problem will be closely managed, and that it will not be as heavy-handed as Maine's response to the last outbreak.
Last time, Maine approved the use of synthetic broad-spectrum insecticides toxic to non-caterpillar insects like bees, aquatic invertebrates and birds to keep trees alive long enough to harvest; this time, narrow-spectrum pesticides will be sprayed on hotspots before a full-fledged epidemic breaks out.
"The budworm response of my parents' generation does not need to be the response of today," said Maine Forest Service entomologist Allison Kanuti. "A successful early intervention strategy can keep forests healthy, supporting not only the economies that rely on them but also maintain wildlife habitat."
Van Hoewyk, the state pesticide toxicologist, said tebufenozide does not build up in the blood, fat or muscle tissue of Maine's mammals, birds or bees, won't leach into the ground water and won't persist in the soil. It is slightly toxic for fish, but they excrete 90% of what they absorb in 15 days.
What if an angler eats that fish? For reference sake, imagine a 2-pound trout had ingested a ridiculous amount of tebufenozide, or 300 milligrams. According to Van Hoewyk's back-of-the-napkin calculations, you'd have to eat a half million such trout in one setting to approach a lethal amount.
"So there's hardly going to be any risk to anglers," Van Hoewyk said.
The risk from Bacillus thuringiensis kurstaki, the spores of a naturally occurring bacterium, is even lower and is approved for use in organic crop production, Van Hoewyk said. It is dormant until activated by the alkaline environment of a caterpillar's gut. Mammals such as humans have a highly acidic gut.
The spraying is part of a $14 million spraying campaign funded with state, federal and private dollars to contain an outbreak that industry projects could cost the state economy an estimated $794 million a year and thousands of jobs, or 12% of the forest product industry's total workforce.
Unlike forest pests like the emerald ash borer, which is an invasive species, spruce budworm is a Maine native. But every 40 years or so, the population explodes, killing up to two-thirds of the spruce trees in its path and 97% of the fir trees. The last outbreak killed an estimated 7 million trees.
But the spruce-fir forests in Maine's colder, higher-elevation regions provide wildlife benefits, too, by creating unique habitats for Bicknell's thrush, which Maine added to its endangered species list last year. Also, fir and spruce forests provide critical deer wintering areas.
A budworm outbreak also could reduce the amount of heat-trapping carbon dioxide emissions removed from the atmosphere by Maine's spruce-fir forests by 5%-16%, depending on the severity, according to Professor Adam Daigneault, director of the University of Maine's School of Forest Resources.
The hotspots popping up in Maine are connected to a massive outbreak in Quebec that began in 2006. By 2020, over 33.5 million acres had been damaged. Aerial spotters found 850 discolored acres in northern Aroostook County in 2021. Last year, the found 3,000 denuded acres near Little East Lake.
While Quebec is in the throes of a full-fledged outbreak, Maine hopes to follow New Brunswick's lead and use targeting spraying in areas where they have found a lot of overwintering eggs to contain budworm population before it reaches full outbreak status.
The state has approved spraying in 34 towns in Aroostook County, from Allagash to Wallagrass. Although the pesticides are considered non-toxic, many of the logging roads that crisscross the largely unpopulated area will be blocked to keep people out of the area during spraying days.
To limit the already low risk, JBI will steer clear of rare butterfly habitats, rivers, lakes and streams and populated areas with high budworm larval counts like Fort Kent and target the upper canopy only, where spruce budworm caterpillars are known to feed, to minimize on-the-ground impact.
JBI planes are equipped with GPS-guided delivery systems, digital mapping and automated navigation to minimize the risk of aerial drift. And the planes will sit idle on windy or rainy days. The state's spruce budworm taskforce will share spraying plans as they develop at
Most environmental advocates didn't want to talk about Maine's budworm spraying plan. Pete McKinley, a senior conservation biologist in The Wilderness Society, was one of the few to voice a concern, but even he admitted that he wasn't sure if he'd ask the state to stop spraying.
McKinley said he isn't sure if the spraying program is worth it or a budworm outbreak is all bad.
An outbreak would wreak havoc on the forest economy, tank the North Woods' carbon storage capacity and destroy habitat for spruce-fir dependent wildlife. But budworms are a native Maine species, and outbreaks are great for many forest songbirds and predators that thrive on edge habitat.
In his long career, McKinley has worked for a land trust, a birding group and a timber management company. He loves Maine's boreal forest, but he doesn't like spray advocates likening an outbreak to a wildfire. Budworm doesn't kill people. It doesn't even kill all spruce or fir.
The last outbreak left a trail of dead trees behind for woodpeckers, he said. It created dense young balsam-fir stands that provided food and cover for snowshoe hares, whose resulting population boom helped increase the ranks of the endangered Canada lynx.
Budworm outbreaks provide "a bonanza of primo bird meat" for more than 40 species of migratory songbirds, McKinley said, including budworm specialists such as the Tennessee, Cape May and Bay-breasted warblers. McKinley spent five years as a forest songbird researcher.
These warblers time their breeding cycles to coincide with peak budworm caterpillar season, relying on them as a source of high-energy food that helps fuel their very costly flight from Central and South America to their breeding grounds in Maine and Canada, McKinley said.
"Will they go extinct or disappear from Maine if they spray?" McKinley asked "No, probably not, but it won't be good for them. Most will switch to another insect. Without any caterpillars at all, though, the competition for what insects remain will be fierce — another stressor on already stressed species."
A 1998 study out of Canada suggests the stress will pose little risk to these forest songbirds. The Canadian wildlife agency found nestling survival and growth of Tennessee warblers in New Brunswick were mostly unaffected by the spraying or the indirect effects of prey reduction.
The study found nests in treated areas had smaller clutches, smaller broods and lower hatch rates than those in untreated areas, but described these differences as statistically significant. Female warblers in spray areas spent more time foraging and less time at their nests, but it did not affect survivorship.
State regulators say they understand the public is concerned about the impacts of aerial insecticide treatments on wildlife. That concern is not only valid, but it is also shared by the people who are leading the budworm prevention effort, said Britt, the agriculture spokesman.
The treatments in Northern Maine are part of a carefully designed, science-based early intervention strategy to prevent a crisis, not respond to one," Britt said. "Acting early allows us to treat fewer acres less often and, more precisely, reduces long-term product use and forest damage."
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