Vermont wildlife officials and syrup producers alike are worried that a recent population boom of a bug with a taste for sugarbush could stress trees and cut into future maple syrup profits.
The forest tent caterpillar, which feeds primarily on sugar maple and white ash, is experiencing its first outbreak in a decade and has been spotted in Orange and Windsor counties, according to Dan Dillner, a forester with the Vermont Department of Forests, Parks and Recreation.
The caterpillar’s eggs are laid each July in treetop twigs in masses of 150 to 200. Because they’re difficult to see from the ground, no one knows how widespread the ongoing outbreak might be when the hungry hatchlings emerge in the spring.
The department flew over the area last month to identify pockets of deforestation associated with the pest, and documented its presence in Chelsea, Tunbridge, Strafford, Royalton, Williamstown, West Fairlee, Vershire and Corinth, said Dillner.
Local deforestation rates are currently lower than the state’s most hard-hit areas, which have been observed during aerial surveys in counties bordering the Upper Valley to the north.
“The hotspot is in parts of Orleans, Washington, Lamoille and Caledonia counties,” said Barbara Schultz, the department’s forest health program manager. “Those are the areas where we’ve had the worst.”
The damage is not limited to Vermont. Some 15,000 acres of damage have been documented in and around the White Mountain National Forest this year, as well.
Schultz said this year’s weather may have fueled both the spread of the caterpillar and the damage it can do to trees.
“Early, warm springs often precede outbreaks,” she said. And during the aerial surveys, it was apparent that trees in areas that were more susceptible to drought, such as those on rocky ledges, had suffered the worst and were most at risk of being killed.
The caterpillars cause consternation for maple sugar producers because in the spring they start to devour young leaves, feeding into late summer.
“It’s a stress on the health of the trees,” said Schultz. “What that means is that trees won’t be putting on wood as quickly. Because it affects the tree’s ability to recover from a taphole, it can mean that sugarmakers have to be a little more conservative in the rate of tapping to make sure that it doesn’t affect the tree.”
An advisory put out by Vermont asks tappers to delay thinning, spare small diameter trees from tapping, and restricting tap placement to no more than one per tree.
The forest tent caterpillar is often confused with other species, such as the eastern tent caterpillar or the fall webworm, but it does not, like those species, build a single, large communal nest that can encompass whole branches and hundreds of individuals.
Instead, during the summer, each individual forest tent caterpillar curls a single leaf around itself and builds a small tent.
Schultz said those watching for the caterpillar at this time of year are most likely to notice leaf fragments on the ground, some of which might be curled up and contain an empty cocoon.
Those who notice signs of the caterpillar are encouraged to contact the department. (Email can be sent from the department’s website at http://fpr.vermont.gov.)
Area maple sugar producers said they hadn’t seen the caterpillars yet this year, but they’re keeping a close watch.
Betsy Luce, owner of Sugarbush Farm, said the bugs are a worry for her family, which taps 9,000 trees on property spread out over Woodstock and Pomfret.
“I know it’s in some areas already, and we’re hoping that it doesn’t come here,” she said.
No one knows exactly what fuels the caterpillars’ population explosions, but they tend to happen about once every 10 years, according to Schultz, with the last significant one peaking around 2006.
Luce remembers that summer well.
“Up toward West Hartford, on the interstate, you could see it was like fall,” she said. “The trees were all brown.”
In Orford, Harry Pease, of Brackett Brook Farm, said he hasn’t seen the forest tent caterpillar in the five years that he’s been tapping 500 trees, but he’s well aware of its reputation.
“It’s certainly something I’m on the lookout for,” he said.
Pease said its getting increasingly difficult to stay abreast of all of the different types of species, invasive and native, that can threaten the health of the local forest.
“There are so many pests out there,” he said. “We’re on the lookout for the emerald ash borer and the hemlock woolly adelgid.”
In order to cope with the growing number of threatening invasive species, citizens and lawmakers both need to take action, according to Matthew Ayres, a professor of biological sciences at Dartmouth College who recently co-authored a paper urging action. The paper notes that there are 47 non-native tree-eating species documented in New Hampshire alone.
“The enormous costs of invasive pests typically fall on land owners and local governments that cannot afford it,” Ayres wrote in an email. “We need to become better — fast — at stopping human-aided transport of organisms among continents.”
The paper’s recommendations include switching away from solid wood packaging, expanding early detection and rapid response programs, boosting international pest prevention programs, restricting imports of live woody plants, and tightening enforcement of existing laws against transport of invasive-harboring materials.
Schultz said the state will continue to monitor the forest tent caterpillar next year, and keep sugarmakers aware of their findings. Outbreaks typically last between two and six years, she said.
Matt Hongoltz-Hetling can be reached at mhonghet@vnews.com or 603-727-3211.