Up until a few decades ago, cold temperatures limited the range of the southern pine beetle to areas south of New Jersey, where winter temperatures rarely dip below minus 15 degrees Fahrenheit.
As its name suggests, the southern pine beetle is associated with pine trees in the southern United States and parts of Central America, where it bores through outer bark, creating networks of serpentine channels as they feed and reproduce in the phloem. Small populations of the beetle live in dead and dying trees, part of the community of animals and fungi that evolved to decompose dead wood, recycle nutrients, and regenerate forests. But sometimes, the beetles increase in number and feed on healthy trees. Such infestations kill large swaths of healthy pines, especially if left unmanaged. In southern timber and pulp plantations, the southern pine beetle has cost the forest industry billions of dollars.
As winter has warmed, the beetle has expanded its range. In 2014, the southern pine beetle destroyed more than 14,000 acres of pitch pine forest on Long Island in New York. The beetle was documented in Connecticut, Rhode Island, and Massachusetts in 2015, but in low numbers.
Anticipating further expansion of the population, University of New Hampshire researcher Caroline Kanaskie wanted to know if there were also populations of southern pine beetle predators in northern New England pitch pine forests, which would help land managers understand resistance to potential future damage.
Working with her PhD advisor Jeff Garnas, she set out traps at 14 sites, hoping to catch the dubious checkered beetle (Thanasimus dubius) and other predator beetles with southern pine beetle pheromone as bait. The experiment worked, as she caught the beetles at all sites. While checking traps last October, she found what looked like southern pine beetles – the size and color of mouse poop – at pitch pine barrens in Waterboro, Maine, and Ossipee, New Hampshire, the northernmost sites in the study.
“I was surprised,” she said. “I never intended to catch southern pine beetle at these locations. I texted a friend who is more familiar with them than I am, because it had been a while since I had seen one, and then when I got back to the lab I put them under the microscope and confirmed the identification.”
“We don’t know exactly what pushes populations from small to outbreak levels,” said Kanaskie. “This has been a question for at least a hundred years. We’ve learned that climate, stand conditions, and predation affect beetle populations, but random, unpredictable occurrences like lightning-struck trees can be catalysts for infestation.”
Kanaskie said there’s no immediate threat to pines in Maine or New Hampshire as no active infestations have been detected, although small groups of infested trees are now appearing in Connecticut, Cape Cod, and parts of New York’s Hudson Valley with increasing regularity. “We do need to think about, as a region, what are we going to do in the face of this upcoming threat?”