Emerald ash borer survives Winnipeg's extreme winter weather

An invasive beetle species is more adaptable to harsh winter weather than previously thought, says a study out of London, Ont.

The emerald ash borer can survive in temperatures that dip as low as –50, and that's not good news for the ash tree population in Winnipeg and throughout Manitoba, Brent Sinclair says.

Sinclair, a biology professor at Western University, and four other researchers published their findings in the Current Research in Insect Science journal on Wednesday.

A previous study said the Asian beetle, which arrived in Winnipeg in 2017, froze to death once the mercury dropped to about –28 C.

However, recent experiments by Meghan Duell, the post-doctoral researcher on the project, found some of the insects from Winnipeg didn't freeze until temperatures reached an average of –46 following the polar vortex that slammed parts of Canada, including Manitoba, and the midwestern United States in 2019.

Sinclair called the findings quite surprising.

"[They're] as cold-tolerant as just about any insects on Earth and certainly as cold-tolerant as you need to be to survive in most places on Earth — even Winnipeg," Sinclair said Thursday.

The beetles either evolved to survive the harsh Winnipeg winters in just a few years, or they have the ability to quickly change their physiology to respond to the frigid weather, he said.

Sinclair said the latter is the primary factor.

"They survive right up until the point that their body fluids freeze, so the trick is to allow themselves to cool down and not freeze," he said. "It seems to be they are doing this by having very concentrated blood."

The borer dehydrates a lot and accumulates glycerol in its blood, which Sinclair said works the same as antifreeze in your vehicle's radiator.

The study says cold tolerance of larvae has not been explored in depth, but Sinclair believes larval cold tolerance is "an essential component" of the borer persisting in Winnipeg.

"If they had been super cold-tolerant as prepupa but had to overwinter as larvae and couldn't do that, then that would have been a problem and they probably wouldn't have survived," he said.

Ash doomed: entomologist

Although the study says the borer has survived the past few Manitoba winters, it remains to be seen how much of a barrier our cold winters are to their spread within the province, Jordan Bannerman said.

"It is quite remarkable that these beetles can survive such extremes. These beetles surviving in a climate much colder than in their native range is a testament to how flexible the biology of insects can be," said Bannerman, an entomology instructor at the University of Manitoba.

The invasive species has only been confirmed among ash trees in one Winnipeg neighbourhood, St. Boniface, Bannerman said.

The city has taken precautions against the beetle since its initial detection, and Bannerman believes that proactive approach has been key to slowing the expected spread of the borer.

The city has approximately 350,000 green ash trees, which comprise close to one-third of the urban forest canopy.

Ash trees are important riparian habitat because they stabilize the banks of many streams and rivers in the province, and provide shade in parks and on campsites, Bannerman said.

While the borer population hasn't increased or decreased, the ecological impact of the beetles will be felt in the future, as will the economic impact of chopping down dying trees and planting new trees, he said.

"Big picture: ash is not going to be in good shape," he said.

"We still do expect, although it may be slower, that this beetle will remove most of the ash from the landscape in Manitoba."