“In that range, we can see mortality typically increase from close to 50 per cent all the way up to nearly 90 per cent,” he says. “Just a small change in temperature can translate to a big increase in mortality.”

Emerald ash borers have killed millions of ash trees in Ontario, Quebec and 20 American states since they were discovered in the United States in 2002. The species turned up in Windsor, Ont. that same year. In the past decade, it has been detected as far north as Sault Ste. Marie, Ont. and as far east as Montreal.

For a place like Renfrew, where the Canadian Food Inspection Agency detected the beetle last June, the -33.3 C temperature the Ontario county experienced earlier this year may have been a blessing in an icy disguise. Taking into account the temperature is a degree or so warmer in the tree where the larvae spend the winter, the Minnesota study estimates as much as 80 per cent of the larvae could die.

“Still, that’s not going to be sufficient to eliminate the emerald ash borer,” says Venette. The cold will, if nothing else, buy municipalities time to come up with a management strategy. “We’re expecting the populations to be reduced substantially, but not eliminated.”