New emerald ash borer research could shed light on how pest holds up to Thunder Bay's winters

New research being conducted by a Canadian federal agency aims to shed light on how an invasive species discovered in Thunder Bay in 2016 will stand up to harsh winters, such as the one the northwest is experiencing now.

The emerald ash borer was first spotted in the city about two and a half years ago. The destructive pest kills ash trees, which were commonly planted along residential streets, threatening widespread damage to urban canopies.

Combating the beetle is a costly endeavour but scientists with Natural Resources Canada are investigating whether temperatures below 30 C can kill the insect or slow down its spread. That type of information could be useful in predicting how the emerald ash borer will behave come spring.

Some ash borers "go through the winter as a larva, which means that in the spring, they're going to wake up and keep feeding underneath the bark of the trees," said Chris MacQuarrie, a research scientist with Natural Resources Canada's Canadian forest service.

"We don't really know anything about how those larva handle winter."

Research has shown that existing ash borer populations in northern Ontario generally spend the winter as larvae, rather than as pupae, as some other populations do, MacQuarrie said, meaning that his research done with the help of a postdoctoral student should be helpful in tracking the beetle's behaviour in the Thunder Bay area.

Beetles from felled trees in Winnipeg are being shipped to MacQuarrie's lab in Sault Ste. Marie, he said, adding that the larvae will be harvested from within the trees' bark, then sent to the University of Western Ontario where they will be exposed to gradually decreasing temperatures.

It's not going to wipe out populations and it's not going to end the problem.-Chris MacQuarrie, research scientist

"We're interested to see how that population handles cold andif... [how] it responds to cold has changed and is different from the populations that were assessed back in the early 2000s," he said.

"If that larval stage is more susceptible to cold, then that has implications for how we think how fast the population will grow or how we manage it or how fast it will kill trees."

But regardless of how low the thermometer plunges in northwestern Ontario, MacQuarrie doesn't believe winter will wipe out the insect.

"It probably will kill some bugs," he said. "It's not going to wipe out populations and it's not going to end the problem."

MacQuarrie cited research done in the U.S. that showed that temperatures in the mid-minus 30s could wipe out about 90 per cent of a given population, but "if you have a big population of insects, even wiping out 90 per cent of them still leaves a lot of bugs left on the landscape to re-infest trees."

He added that in the northwest, ash trees are usually found in cities as street trees and there are some in the bush, although not as many as in southern Ontario.