Spruce Budworm Population Tracked by Landowners Across Northeast Pheremone Traps Help to Gather Data
Brett Mitchell has a vested interest in keeping tabs on the population of spruce budworm moths — he and his son own a 45-acre Christmas tree farm — 45,000 balsam fir trees — in St. Agatha at the northern tip of Maine.
So, when he heard about a program looking for would-be citizen scientists to put out and check pheromone traps for the moths, he signed up. “We were worried about an infestation of the budworm. And we figured the best thing we could do is to get involved,” Mitchell said.
Mitchell is one of 37 Mainers taking part in the Budworm Tracker Program. In all there are now nearly 400 people across six eastern Canadian provinces and Maine helping gather data about moth numbers that will help scientists study the unfolding outbreak of this cyclical native insect pest.
Budworm Tracker, which is administered by the Canadian Forest Service, is in its second year. “It’s an ongoing project that will run into the foreseeable future,” said Emily Owens, the project manager.
Owens said people sign up for a variety of reasons. “Some people might have a woodlot, or they might have a grandchild that’s interested in science or biology and want to foster that, others like the sense of collaboration and others remember the last outbreak.”
That last outbreak reached its peak in Maine in the1970s. It resulted in millions of acres of defoliated spruce-fir forest across eastern North America. In Maine it killed 20 to 25 million cords of spruce and fir, spawned a controversial spray program and precipitated a rush to salvage the dead trees.
The spruce budworm is one of the most damaging pests of conifers. The larvae, or caterpillar, of a nondescript gray moth, it feeds on the needles of spruce and balsam fir trees. Populations of the moths can remain at low levels for years. But outbreaks occur every 30 to 60 years. Then it’s a slow motion disaster, with huge numbers of caterpillars munching their way across the landscape, defoliating trees by the millions and turning the northern forest the color of dried blood.
In 2007 an outbreak began on the north shore of the St. Lawrence River in Quebec and has since spread to the south shore. Scientists are warning that the outbreak could spread to Maine in a few years.
While the spruce budworm has been the subject of many studies, there are lots of things scientists don’t yet know about it, including what prompts an outbreak and why and how it spreads. But they’re working to find answers.
To do it they use something that wasn’t available during the last outbreak — pheromone traps.
Many insects communicate biochemically. Pheromone traps take advantage of that. They use a synthetic pheromone that attracts insects looking for sex. The common Japanese beetle trap is a pheromone trap. Apple growers put out pheromone traps against pests like codling moth and apple maggot fly.
In the case of the spruce budworm, the pheromone used in the traps mimics the one given off by female moths, attracting males wanting to mate. This time of year — late June into September — the moths are flying and pheromone traps need to be set up and checked for moths.
The Maine Forest Service didn’t have pheromone traps during the last outbreak, said Maine State Entomologist Dave Struble. They used light traps. They have an advantage in that they attract spruce budworm moths of both sexes. The problem is that they attract moths of many species. Separating the target moths from others to get a true picture of spruce budworm takes a lot of time.
Struble said the Maine Forest Service continued to monitor moth populations even after the last outbreak waned in the 1980s. For years it maintained 80 to 100 permanent trapping sites across northern Maine. That number has grown to some 400 sites stretching from Oxford and Franklin counties to Washington County.
The MFS sites use three pheromone traps each, where the Budworm Tracker program deploys them individually.
Maine Forest Service entomologist Allison Kanoti said the trio of traps is arrayed in a triangle about 130 feet apart, in patches of spruce and fir at least 25 acres in size, where the trees are at least pole size and starting to bear cones. “These are the things that are attractive to the budworm,” said Kanoti, “It’s not just the trap that is attractive, it’s the environment.”
Under the MFS program the white plastic traps are maintained by landowners, who check them at the close of the season, put any moths in a plastic baggie and ship the bags to the Forest Service.
“From that you can develop information on the intensity of the population. That doesn’t mean that those moths came from that individual stand of trees, they could be from further away or they could be local moths,” said Struble. “But you get a chance to look at the pattern on the landscape and how it looks compared to last year.”
Last year all the historical MFS trapping sites recorded some moths, and 98% of all sites (new and old) caught moths. “That was not true a few years ago,” he said. “There is a little shift in hot spots from two years ago to last year. But it’s still an extremely low population.”
The pheromone trapping programs are a bargain, said Struble. It costs about $10 per site a year, and because the work of putting out and checking the traps is handled by landowners or citizen scientists, there’s virtually no additional expense.
Owens said it’s evident that the current outbreak is spreading. But the Budworm Tracker program “will need several years of data before we have any conclusive results.” The program got a good response from Mainers when it sought volunteer pheromone trappers for the 2016 season”, she said. ”People jumped on the opportunity immediately. Our goal is to have a good distribution of citizen scientists with traps set up across Maine. Next year we hope to target gaps in our grid.”
That enthusiastic response by citizens doesn’t surprise Owens. “People for economic, ecological and spiritual reasons are extremely invested in the forest,” she said. “They see the value in it and want to do what they can to protect it.”
Kanoti agreed. Mainers have, time and time again, responded to requests for help in collecting information, she said. “Part of it is probably that there are folks who are tied some way to the forest. We live with it and depend on it for our livelihoods. People generally step up when we do ask for volunteers.”
As for Brett Mitchell, he said the Mitchell Family Christmas Tree Farm’s budworm trap gets checked pretty much every other day by himself, when he makes the trek up from his home in Bass Harbor, or by his on-site farmhand.
“So far, by the way, we haven’t caught any moths at all. The only thing we’re catching is spiders,” Mitchell said. But that doesn’t disappoint him. It means he can continue working toward his first Christmas tree sales next year rather than fighting a budworm infestation. Only time will tell whether that remains the case.
Joe Rankin writes on forestry and nature. He lives in New Sharon.