More Canadian cities will experience damage from the emerald ash borer than previously thought. As a result of climate change and fewer days of extreme cold, the beetle may eat its way further north than originally estimated.

Kim Cuddington, a professor of biology at the University of Waterloo, led the team that produced a probability map for North America showing where the emerald ash borer is likely to kill trees.

"We ran specific predictions to help Canadian cities decide if they need to make plans before they're affected," said Cuddington. "Calgary is likely to experience damage, as are Thunder Bay, Prince George and Winnipeg. Edmonton and Saskatoon are less likely, but they should remain vigilant."

So far, the wood-boring beetle has wiped out tens of millions of ash trees and will likely cost municipalities $2 billion. Still, everyone expected the species' rapid migration would be stopped by Canada's extremely cold temperatures.

"This should be a wake-up call for how we think about invasive species," said Cuddington. "We need to develop preemptive measures as well as mitigate potential impacts. By the time we see the damage, it's almost too late."

According to previous studies, prepupae can survive in temperatures as low as -34ºC. Cuddington and her group confirmed the temperature found under the bark where the insect overwinters is warmer than the outside.

"We took a different approach from traditional range maps and charted the statistical probability of under-bark temperatures being above this lethal limit for at least six years," said Cuddington. "That's just long enough for the insect to kill its host tree."

This is one of the first studies to couple an extensive empirical data set with measures of climate variability using a mechanistic modelling approach. Cuddington says researchers need to think more carefully about how a changing and unpredictable climate relates to the biology of an invasive species and their risk of doing damage, both economically and ecologically.