Vivian Thomas of BC Forest Services in Victoria (250-387-5728) says "the current cold weather that we are having in the interior is not cold enough to have an impact on Mtn Pine Beetle populations. For this time of year it must be -35 to -40 deg C for several straight days to kill off the pine beetle. The beetles develop a natural anti-freeze that protects them from cold weather. If the cold snap had come earlier in the fall and been -25 deg C for several straight days, then it could have killed off populations when the beetle was more vulnerable."
This from the Canadian Forest Service's website:
"The outbreak is likely to continue until an early cold winter kills overwintering larvae. In fact, it was two back-to-back unseasonably cold fall periods in 1984 and 1985 that caused the collapse of the Cariboo-Chilcotin outbreak. In both of those years, early sustained temperatures in the -30 to -40 deg C range were experienced."