Will Sub-Zero Temperatures Kill the Beetles That are Killing Canadian Forests?

Issue: 
March-April 2008

SADLY, THESE PESTS MAY turn out to be freeze-resistant, at least in our climate. Dave Roden, an entomologist with the Canadian Forest Service (CFS) at the Great Lakes Research Centre in Sault Ste. Marie, has been studying the “super cooling point” of the Asian long-horned beetle (ALB). That’s the point at which the last drop of water freezes in living tissue.

Roden believes the super cooling point for the ALB is –26 C. As the weather turns cold, the insects undergo biochemical changes and produce glycol, or sugar, which prevents them from freezing unless they reach the super cooling point, “Just like the antifreeze you put in your car.”

“Insects die when ice crystals form and destroy the cell walls.”

But, he adds, some insects are “freeze-tolerant.” “They quite happily freeze. You can take the temperature down to where you want, and when the temperature comes back up, they come back to life.”
Roden has exposed some beetles to temperatures as low as –40 C for 24 hours and seen them revive, mature and reproduce the next generation of insects.

His research is new, and he’s finding it difficult to get enough specimens to test. “We’re not 100 per cent sure, but it looks like the ALB is freeze-tolerant.”

While he hasn’t studied the emerald ash borer (EAB) – which is now in Toronto and has killed about 1 million trees in southwestern Ontario – Roden says it appears to have a similar super cooling point to ALB beetles. Both originate in China, where climate extremes are the norm.

Scientists in BC and Alberta have been studying the effect of extremely cold temperatures on the native mountain pine beetle, which has killed millions of hectares of pine forest.

In Edmonton, Barry Cooke, also an entomologist with CFS, has observed a 14% mortality rate among beetles in the service’s outdoor “beetle garden” during the early part of the winter.

But after January’s cold snap, when the temperature plunged to –39 C outside their lab, he found a 93% mortality rate. Researchers also measured beetle mortality in their lab and found that at a temperature of –37 C, 50% of the beetles died.

“They started dying the moment they crossed the lethal threshold,” he says.

Cooke notes, some mountain pine beetles have survived temperatures of –46 C. “We don’t know what accounts for the unusual cold hardiness, but there is potential for these (northern Alberta) populations to start to evolve cold tolerance on a wide scale and become the founders of a new race or sub-species of mountain pine beetle.”

On the plus side, the extreme cold will likely stem the beetles’ widespread progress through the province. “We have a temporary reprieve because of the cold,” says Cooke. “We were facing an impending disaster in Alberta. Now we are facing a situation of heightened uncertainty.”

At the University of Northern British Columbia, forest entomology professor Staffin Lindgren says the pine beetles, which have left the pine forests an eerie rust colour, adapt themselves to the cold as the winter progresses. At the end of the summer, they start preparing for winter by producing glycol in concentrations that increase through the fall and winter.

The beetle populations tend to crash if there is a sharp cold snap early in the fall, more so than in the deepest winter. Says Lindgren, “ A temperature of –30 C in October is much harder to deal with than –40 C in January.”

- Leslie Scrivener, reprinted with permission – Torstar Syndication Services

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.