One of the most destructive pests in Maine’s forests is back.
The eastern spruce budworm is a species of moth whose caterpillar voraciously eats the needles off of coniferous trees. The insect is native to Maine and naturally has an outbreak cycle of 30 to 60 years.
“When the needles have been chewed off, the trees grow less,” said Neil Thompson, assistant professor of forestry at the University of Maine at Fort Kent. Thompson explained that the moths lay eggs in summer, and then the larvae burrow into the bud in the spring and eat the needles when they sprout. “It’s a fascinating bug.”
Maine has experienced outbreaks of spruce budworm in the past, most notably in the late 1970s and early 1980s. The reemergence of the pest has prompted the University of Maine to reopen a state task force to control its population and debut a new lab, the first of its kind in the country, to keep up with testing for its presence.
The spruce budworm isn’t inherently bad. Many birds prefer to feed on it, and there are natural levels of the insect’s population across the state. However, once the population exceeds a level that natural predators can keep in check, called “iruption threshold,” it can wreak havoc on the forests that are essential to Maine’s timber economy.
“If an outbreak got out of control, that could tear the wood supply apart,” Thompson said. “If it tears the center out of softwood resources again, we’d have a serious problem.”
Even if a tree manages to survive a spruce budworm siege, it is stressed and more vulnerable to pathogens, drought conditions and other potentially fatal stressors. Add that to the research from UMaine which shows that the tree stands are too dense, meaning that trees aren’t getting the resources they need.
An aerial view of the Maine forest in the wake of the spruce budworm epidemic in the 1970s and 1980s. Credit: Courtesy of the Maine Forest Products Council.
The stress that the pests exact on the trees can make conditions more dangerous for forestry workers, too. Spruce budworm attacks sometimes only kill the top of the tree, Thompson said, leaving dangerous “widowmakers” that can fall onto unsuspecting passersby.
In 2006, researchers in Maine caught wind of a spruce budworm outbreak in the Canadian province of Quebec that looked as intense as the one from the 1970s and 1980s and began monitoring the insect more closely.
In 2019, Thompson said, a population of spruce budworm moths finally reached northern Maine.
“We pretty much got smeared with budworms on two evenings,” Thompson said. “It’s the most we’ve seen since the 1980s.”
Researchers count the number of larvae on a branch using a process called L2 sampling, which dissolves the silk on the branch and makes it possible to count the larvae. Thompson observed plots with high levels of spruce budworm population — up to 28 per branch, where the threshold is considered to be seven per branch.
In response, UMaine has not only reactivated its spruce budworm task force — a collaboration between the University and partners like the Maine Forest Service and Maine Forest Products Council — but it also opened a new lab so that there are testing capabilities for spruce budworm in the state.
Previously, L2 testing for monitoring efforts could only be done by shipping off samples to Canada. Now, the lab in Maine will be able to serve its landowners as well as those other states that experience spruce budworm outbreaks, like Michigan, Vermont and New Hampshire.
“We’re basically taking ownership of the processing for the state of Maine and the United States as well,” said Angela Mech, assistant professor of forest entomology at the University of Maine.
Mech and Thompson are the principal investigators on a Cooperative Forestry Research Unit grant that provides more than $400,000 in funding for spruce budworm monitoring in Maine over the next five years. The Spruce Budworm Testing Lab is funded through that grant and will conduct the testing of 900 branch samples from 300 sites across Maine to provide a yearly snapshot of spruce budworm population densities.
The lab wil also conduct fee-for-service testing at a rate of $150 per site for landowners who submit branch samples. Information on how to correctly collect branch samples is available on the lab website.
Researchers hope that frequent monitoring will prevent a serious outbreak in Maine, but even if there is one, there are new, more targeted methods for controlling it.
The usual method for managing populations involves widespread insecticide spraying of infected areas, but new methods out of New Brunswick involve early intervention using a microbial pesticide called Btk that is isolated to only kill caterpillars as opposed to insects broadly.
In New Brunswick the government has publicly funded these intervention measures, but that would not be the case in Maine.
“What worries me is the small private woodlots in the St. John Valley, there’s very little you can do on a hundred-acre parcel,” Thompson said. “It’s fragmented, there’s a lot of neighbors, it’s very expensive, there’s a lot of things working against you.”
Landowners will have access to this new lab much closer to where they are to test their woodlots early and often.
“There are extra challenges that come with small ownership we hope to support with the lab, but there’s challenges,” Thompson said. “Hope for the best, plan for the worst.”