Maine Forest Service releasing wasps to kill invasive forest beetles

Wasps like this will be released in northern Maine Thursday to curb the emerald ash beetle population, the Maine Forest Service said.
Wasps like this will be released in northern Maine Thursday to curb the emerald ash beetle population, the Maine Forest Service said.US Department of Agriculture Agricultural Research

The Maine Forest Service is releasing wasps Thursday in northern Maine to control an invasive pest species, officials said.

The Forest Service will release three tiny non-stinging species of wasps, including one less than a millimeter long, in Aroostook County, the northernmost county in Maine, Colleen Teerling, a forest entomologist at the Forest Service, said. The Forest Service is working with the US Department of Agriculture to eradicate emerald ash borers, which are invasive green beetles that have killed millions of ash trees since they first came to North America in 2002.

The borers were discovered in Maine in 2006, Teerling said.


“EABs have killed over 99 percent of ash trees it attacks, so there’s very little resistance. Using biological controls is our best bet in keeping this entire group of trees on our landscape in the long term in North America. If we didn’t do this, we might have 16 species of ash trees go extinct in North America,” Teerling said.

The emerald ash borers, which came from Asia on a ship, lay eggs in ash tree bark. The larvae feed underneath the bark for one or two years before they leave the tree, according to the Emerald Ash Borer Information Network.

The wasps parasitize the emerald ash borers’ eggs to reduce the borer population, Teerling said. Two of the three wasp species lay eggs inside larvae underneath the bark, and the other species lays eggs in larvae on top of the bark.

“[The wasp] lays its eggs in EAB eggs, and instead of the borers hatching from the egg, a whole bunch of [wasp] parasites will come out of that egg and will go out and look for more EAB eggs to stop it from hatching,” Teerling said.

The three wasp species are Oobious agrili, Tetrastichus planipennisi, and Spathius galinae. Most of the ash trees already affected by the borers will die, Teerling said, but future trees may be saved by these wasps. The Forest Service and the USDA will not know if the wasps saved the trees for another 50 years.


“We’re hoping it will help save the trees coming up in the next generation. It will certainly not get rid of EABs, but we’re hoping it will help create balance so EABs won’t be well enough and our trees are able to survive,” Teerling said.

Other states battling emerald ash borers, including Massachusetts and Michigan, have released wasps to curb the borer population, according to the USDA. Canada is also using wasps to reduce its infestation. The emerald ash borers were first discovered in Detroit in 2002 and quickly spread throughout the continent, Teerling said.

“It’s very easy for people to move [emerald ash borers] around without knowing it. Once we found it in North America, it moved in firewood and other things inadvertently,” Teerling said.

The Forest Service will only release a small number of wasps because the insects are difficult to rear, Teerling said.

Emerald ash borers were found in Aroostook and York Counties in 2018, the Forest Service said. The wasps were produced by the USDA in Brighton, Mich.

Alyssa Lukpat can be reached at alyssa.lukpat@globe.com. Follow her on Twitter @AlyssaLukpat.