Southern Ontario's cold snap will hurt emerald ash borer, but won't eradicate it: Experts

The recent frigid temperatures in Ontario may hurt the emerald ash borer population, but it's not enough to get rid of the pest completely, scientists say.

'We're still going to have them next spring when it finally warms up,' research scientist says

Emerald ash borer can survive Canada's cold winters and withstand temperatures as low as –30 C, scientists say. (Minnesota Department of Natural Resources/The Associated Press)

The recent frigid temperatures in Ontario will likely impact the emerald ash borer population, but it won't get rid of it completely, experts say.

Christian MacQuarrie, a research scientist with Natural Resources Canada's Great Lakes Forestry Centre in Sault Ste. Marie, said the temperature has to hit –30 Celsius before it impacts the pest.

"If temperatures don't get that low, then the insect doesn't die. It's able to protect itself by sort of making these antifreeze proteins," he said.

"Emerald ash borer could probably survive throughout most of Canada through a typical winter," he said. "It might knock the populations back, it might sort of slow them down, but it's not going to eradicate them. It's not going to get rid of them. We're still going to have them next spring when it finally warms up."

Found in five provinces

Emerald ash borer is an invasive species that first appeared in Canada in 2002. Natural Resources Canada says the females lay eggs in the crevices or under the bark of ash trees. When the larvae hatch, they tunnel further into the bark until it hits the part where the bark and the wood of the tree meet.

There, it will eat and create a S-shaped tunnel where they'll grow before chewing a whole into the wood or bark where it will pupate. That's the stage it's in when winter arrives.

The borer is found in five types of ash trees in Canada: green, white, black, pumpkin and blue.

The Co-operative Emerald Ash Borer Project has mapped locations where it has been found. While it's mostly in southern Ontario, there are outliers, including Thunder Bay and Manitoulin Island. The map shows the pest is in five provinces and 35 states south of the border. 

MacQuarrie says emerald ash borer has been found in Winnipeg in Dec. 2017 and was found in New Brunswick and Nova Scotia in 2018.

Lines beneath the bark on an ash tree show the path which made by borer larvea. (The Associated Press)

Can't get rid of it in one area

Kim Cuddington, a University of Waterloo associate professor of biology who has studied emerald ash borer and other invasive species, says the air has to be –30 C to see about a 75 per cent mortality rate in the prepupa stage, which is when the borer lives under the bark of the ash tree. Wind chill is not a factor, she noted.

The mortality rate drops to 50 per cent at –25 C.

"Probably not a lot of mortality," she said of temperatures experienced in a typical southern Ontario winter.

Even if one area of the province were to see prolonged, cold temperatures, it doesn't get rid of the threat, she noted.

"To take a ridiculous example, if someone took an umbrella on the landscape and froze that area of the landscape down to –40 C, killed all the emerald ash borer and then lifted the umbrella up, that means, yes, there's no emerald ash borer there right now, but it's all surrounded by emerald ash borer that's going to move into the area," she said.

'It's still spreading'

Right now, forestry scientists are trying to manage the invasive species.

The cold event the province recently experience will "probably kill a bunch of them" but forestry workers still need other tools like insecticides and education. MacQuarrie says it's important to remind people not to move firewood around the province that could contain wood with emerald ash borer.

Current research is also looking at what's next for the insect and trees, he said.

"We're still trying to figure out how emerald ash borer and ash [trees] will interact on the landscape 10 years, 15 years from now, when that big wave of mortality of ash trees has passed over us," he said. "It is still spreading and there's lots of places where it's new."


To encourage thoughtful and respectful conversations, first and last names will appear with each submission to CBC/Radio-Canada's online communities (except in children and youth-oriented communities). Pseudonyms will no longer be permitted.

By submitting a comment, you accept that CBC has the right to reproduce and publish that comment in whole or in part, in any manner CBC chooses. Please note that CBC does not endorse the opinions expressed in comments. Comments on this story are moderated according to our Submission Guidelines. Comments are welcome while open. We reserve the right to close comments at any time.