Hate the cold? Mountain pine beetles do too

Published: August 6, 2020

MPB killed pine photo – The needles of a lodgepole pine tree turn red a year after it was killed by mountain pine beetle. The needles of a lodgepole pine tree turn red a year after it was killed by mountain pine beetle. Courtesy Alberta Agriculture and Forestry

If you live in Wild Rose Country you’ll know January 2020 was some cold—so cold the Calgary Zoo’s King Penguins were kept inside. So cold the Ice Castles in Edmonton’s Hawrelak Park closed. So cold a weather station north of Grande Cache logged -49.7°C.  So cold, that even some of the province’s invasive mountain pine beetles felt the chill. 

Alberta’s recently-released spring surveys show beetle populations in the Grande Prairie, Slave Lake, Whitecourt and Edson areas were “knocked back slightly,” by last winter’s polar cold, says Caroline Whitehouse, forest health specialist with Alberta Agriculture and Forestry. Further south, though, Whitehouse says “overwintering success was much better” for the pine-killing invaders along the eastern slopes of the Rockies. 

Mountain pine beetles are susceptible to temperatures the -40°C range, but because they spend their winters as snug as a bug in a pine, it takes time for the cold to penetrate insulating layers of bark and snow. If temperatures inside the tree reach -35°C, for example, Whitehouse says about half the beetle larvae will die. That sounds impressive, but with millions of beetles gnawing their way through the forest—and the insect’s well-earned reputation as a prolific breeder—it’s not good enough. 

“You’d need 90 to 95 per cent mortality to slow an outbreak,” she says. “One female will lay 60-80 eggs, and two-thirds of those are going to be female. Within a generation, one female beetle can produce 1,600 new females.” 

The good news is the outbreak in north-central Alberta’s boreal forest seems to be stalling, thanks to the province’s efforts to find, cut, and burn infested trees. And while this dismal, rainy summer is a bummer for heat-starved residents in the Edmonton region, Whitehouse says it’s a drag for the beetles, too. Cool summers slow the critters’ development, so “we would normally see fewer beetles” going into the winter. 

That’s the silver lining. But “in Alberta, the mountain pine beetle is definitely a fact of life,” Whitehouse says. “Even if we have this cool summer and another cold winter, the beetle will still be in the province.”

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