Temperatures in beetle-hit communities in northern British Columbia and Alberta have hovered between -20 Celsius (-4 Fahrenheit) and -35 Celsius (-31 Fahrenheit) in recent days, but killing the insects requires it to be colder than that for several consecutive days.

"This is not having much of an impact on mountain pine beetles," said Michel Proulx, a spokesman for Alberta Sustainable Resource Development.

The insects have lived on lodgepole and ponderosa pines in Western Canada for thousands of years, but nature controls major outbreaks of the insects with extreme cold that freezes them in the trees or through forest fires.

The area has not had the required cold snap in recent years, and efforts to fight fires to protect the timber supply and area communities have increased the number of older trees that are more susceptible to an insect attack.

The beetles also have their own defenses against the cold, building up their natural antifreeze levels as the temperature drops. This cold snap in may have come too late to do much damage.

"At this stage, their antifreeze is very well developed," Proulx said.

Some of the areas with low temperatures have also had heavy snow, which supplies additional protective insulation for the insects now buried beneath the tree bark.