January’s record high average temperature throughout Maine foreshadows a threat from a new pest that could attack the iconic trees spanning Maine’s southern coast to the mountaintops of Acadia National Park.
Found in 2021 by a University of New Hampshire researcher in York County, southern pine beetles — each about half the size of a grain of rice — can marshal into swarms that attack and tunnel through pitch pines, trees appreciated for their scraggly beauty and the plants and animals that live near them, such as the pine and prairie warblers and the pine devil moth.
They can kill a tree within a few weeks, scientists said, and already have killed thousands of acres of pine forest in the southern U.S. So far, only a couple dozen beetles have been found in Maine, and many of those died off during the cold snap in February 2023. But warming weather is bringing them north from their southern U.S. roots, with the beetle already having expanded to Nantucket and Martha’s Vineyard.
“Climate change is definitely a factor in this northward spread of southern pine beetles,” Caroline Kanaski, the UNH doctoral student who discovered the presence of the beetles in Maine, said. “We’ve had a lot of coastal storms recently and anything that’s going to stress our trees is an opportunity for forest pests to impact them.”
It is not clear when the southern pine beetles might proliferate in Maine, but fall hurricanes are thought to be a factor in bringing them north. Yet Maine Forest Service entomologist Tom Schmeelk said his level of worry about them is already at a 5 or a 6 on a scale of 10 because of their destructive abilities.
“The coastal and inland [pitch] pine barrens are very important ecosystems for the plants and animals they support,” he said. “Economic impacts of the pitch pine are its tourism and erosion prevention benefits.”
The southern pine beetle favors pitch pines, but it also attacks red pines and jack pines. The three pines together make up about 1 percent of the forested area of Maine, the forest service estimated. Schmeelk, who collaborates with Kanaskie on a statewide early warning network for insects not previously in the state, said the potential impact of the beetles’ attacks in Maine is more on the environment than on forestry.
Most southern pine beetles will die if it gets too cold at minus 17 degrees Fahrenheit, Kanaskie said. The state’s January average temperature of 24.3 degrees was 11.2 degrees warmer than what is considered an average January, according to the National Oceanic and Atmospheric Administration. It followed a warmer-than-average December and warnings by scientists that the climate is becoming warmer.
Despite their diminutive size, southern pine beetles can secrete chemicals to amass by the thousands and efficiently attack pitch pines. Their Latin genus name means “tree killer.” They use certain chemicals to attract other beetles to join them in the attack. When there are enough, they use other chemicals to discourage other beetles.
“The southern pine beetle relies on the number of beetles attacking in order to overwhelm the defenses of the tree,” Schmeelk said.
The female southern pine beetles select a pine tree as the initial target, usually a tree damaged by heavy winds or areas where the trees may not have been thinned and are too close together, he said. The females drill down to the cambium — the growing part of the tree’s bark — and create “pitch tubes,” which look like popcorn on the trunk of the tree.
The drilling of the holes and tunneling under the bark choke off the tree’s ability to move water from its roots to its needles, and it dies.
No trees in Maine have been successfully attacked by the southern pine beetle, because the insects’ numbers are still so low. No beetles have made it yet to Acadia National Park.
Kanaskie will continue her studies of the pitch pine locations there this summer, looking particularly at temperature data from pitch pine areas to predict whether the southern pine beetle could survive there.
It is important research, because the craggy trees and the plant and animal life around them are important for the views visitors will take home from the park, Jesse Wheeler, biologist for Acadia National Park, said.
“Acadia is the northernmost range limit of pitch pines in the U.S.,” he said. “We have a globally rare community of pitch pines with a relatively uncommon low shrub called the broom crowberry.”
Kanaskie may be looking at a potential localized impact of the southern pine beetle, but she is taking an expansive view because of the amount of travel by people that could spread the beetles and the effects of the warming climate.
“With climate change and the interconnected nature of our world, I think we will continue to see new invasive insects in New England,” Kanaskie said. “For native insects like the southern pine beetle, we will see them in new places.”
Lori Valigra is an investigative environment reporter for the BDN’s Maine Focus team. She may be reached at lvaligra@bangordailynews.com. Support for this reporting is provided by the Unity Foundation and donations by BDN readers.