The invasive emerald ash borer that has been decimating American ash trees has not been found in Maine — not yet, at least.
For another summer season, the Maine Department of Agriculture, Conservation and Forestry has not found any emerald ash borers in the statewide network of 900 sticky traps and surveillance trees.
Since it was first found in Michigan in 2002, “We’ve been watching it move kind of like wildfire throughout the U.S. and a little bit through Canada,” said Colleen Teerling, an entomologist with the Maine Forest Service Insect and Disease Lab.
“We know we’re not going to be able to stop it or eradicate it, but we are hoping we could slow down the spread of it. We have a lot more tools since it was first discovered.”
Without a major predator in North America, the destructive green beetle native to northern Asia and Siberia has killed millions of ash trees in at least 26 states, with the adults feeding on ash leaves and the larvae eating the inner bark, cutting off its nutrients. So far, the borer has been found in every state in the Northeast except Maine and Vermont, according to information collected by the U.S. Department of Agriculture.
Unlike other invasive insects susceptible to strong winters, like the woolly adelgid infesting East Coast hemlock trees, Maine’s winters offer no protection from the ash borer. “The critter comes from Siberia. It’s going to laugh at our winters,” Teerling said.
In states like Kentucky, New York and Pennsylvania, the borer has crippled industrial uses of ash for timber, firewood and baseball bats — killing some 97 percent of trees infested, according to Teerling.
In Maine, the likelihood of future infestations has left tribal communities and others concerned about the next generation of ash trees for baskets, snowshoes, and woodcrafts, as well as for a shared cultural history. Ash trees are central to the Wabanaki Confederacy origin story, in which the Passamaquoddy, Penobscots, Maliseets and Micmacs arise from four white ash trees marked by the hero Gluskap.
While there is no one easy solution to the ash borer on the horizon, there are reasons to be optimistic, Teerling said.
In Maine, the three ash species (brown, green and white) comprise about 2 percent of the state’s total forest cover and about 4 percent of hardwood trees, Teerling said. Those populations are so spread out, scattered across woodlands from southern Maine to the St. John Valley, that they’re all unlikely to be infested at once. Some may even remain untouched and continue producing offspring for decades to come, Teerling said.
“We just don’t know how the insect is going to move,” she said. “We don’t think it’s going to be a death knell for ash trees all around the state.”
Among the options for weathering the borer storm are biologic controls — using predators of the borer to help offset losses — and seed repositories that prepare for new generations.
Federal and state agencies in the states with infestations have released parasitic wasps native to China that lay eggs inside ash borer eggs, preventing them from hatching. Those might make a small dent, and help at least a few ash trees survive to reproduce, Teerling said.
“It’s going to take a while for the parasitic wasps to catch up. We’re not going to save the trees that have been infested, but when the new generation comes up, the hope is those will be protected.”
After an infestation, for instance, groups that have been building banks of ash seeds, including the Aroostook Band of Micmacs, will be able to help replant areas that are affected.
Teerling said Maine can continue to keep the ash borer under control if residents and visitors alike are careful not use any out-of-state firewood. Out-of-state firewood has been banned since 2010, as a measure instituted to prevent the spread of the ash borer and the brown spruce longhorned beetle.
Currently, the closest ash borer infestation is around greater Concord, New Hampshire, Teerling said. Without human influence — such as Granite Staters bringing firewood to Vacationland — she suggested infestations will creep towards Maine at a rate of about half-a-mile or a mile per year.
Reports of potential evidence of the emerald ash borer and other invasive insects can be shared with the DACF through an online form or by calling 207 287-2431.
