Cold snap won’t stop mountain pine beetles, U of A scientist says
Frigid as it feels, the white-knuckled cold snap gripping Alberta isn’t severe enough to put a halt to an infestation of mountain pine beetle threatening the province’s forests, scientists said.
Temperatures need to dip below about -30C for four or five consecutive weeks to kill nearly all pine beetle larvae nestled inside tree trunks, said Nadir Erbilgin, a University of Alberta professor of forest entomology who studies the pine beetle.
“I’m not sure we will ever get those good old days of freezing, long-lasting temperatures in Alberta,” he said in an interview Monday.
At last count in 2018, nearly half of Jasper National Park’s pine forests had been infested by the beetle’s larvae. Beetles lay eggs inside the trees in September. Those eggs develop into hundreds of larvae that spend fall, winter and spring gobbling and burrowing through the tree’s interior, Erbilgin said.
A female beetle can lay as many as 250 eggs a season, he said. Even if three-quarters of them die, their numbers still rise exponentially with each generation.
Ultimately, pine needles on infected trees turn red and the tree dies, becoming a wildfire hazard. In summer, fully developed beetles fly off in search of a new tree to burrow into.
Cold helps control the spread, but won’t stop it.
About 2.3-million hectares of provincial forest have been infected with mountain pine beetle since the pest penetrated the province in 2006, said Caroline Whitehouse, a forest-health specialist with Alberta Agriculture and Forestry.
Before 2006, winter temperatures were cold enough to stop the beetle’s encroachment across the Rocky Mountains from B.C.
Although much of Alberta has been subject to extreme-cold warnings for more than a week, temperatures have been more variable in Jasper, which hit a high of -9.5C on Feb. 7, according to Environment Canada’s weather data.
The timing of the chilly temperatures is relevant, Whitehouse said. Beetle larvae are more susceptible to cold when they’re younger in autumn, she said.
It also depends how deeply larvae are burrowed into the tree, as bark can buffer them against the cold.
Temperatures of -35C will kill some beetles, but not enough to halt the current outbreak, she said.
“There’s just so many beetles out there. You really need to have high mortality levels.”
However, the deep freeze could help reduce the amount of work the agriculture and forestry ministry will have to do next winter to control the spread of the pest, she said.
This winter, crews will knock down and burn about 100,000 infected trees by the end of March to prevent the pest’s spread.
Pine forests in Lac La Biche, Whitecourt, Edson, Rocky Mountain House and Calgary are now susceptible to mountain pine beetle infestation, which could affect the 14 logging companies operating within Alberta forests.
Although the mature beetle often hops to nearby trees to continue its destructive ways, Erbilgin said he last year caught beetles that had travelled 200 km from Jasper to the Edson area after a particularly windy day.
“This year is going to be very critical,” he said. “If there’s a wind event, I can tell you they’re going to spread.”
The pine forest around Hinton will likely be the main battleground for preventing the spread of pine beetle this summer, he said.
“Everybody is screaming loud — we’ve got to do something about it. And they are absolutely right.”