The super cold is what gets that darn beetle. A forester told me that the best is when it starts to warm up a bit in the very early spring and then drops back very cold in the single digits or less. The Beetle has kind of a antifreeze in them the warm weather turns it back around and they kind of come back to life. Then the super cold hits and they can't react to it. Kills them. Not sure if that's the whole story but I do know the super cold is what is needed to take them out.
They (forest management folks) look for a sustained (1 week) -30C or colder as a reliable killer of the mountain pine beetle. We didn't really get that this winter up here, so it's looking to be another year of controlled burns to head them off. They conducted a large one just outside of the Banff park boundary last year.
It's been demonstrated time and again that if you try to completely suppress wildfires (as was done in the national parks up here for decades), you end up with catastrophic fires when they happen. Deadfall accumulates and is perfect tinder. When a fire starts (whether through negligence or nature) it spreads quickly to the tree-tops and annihilates the trees, more or less sterilizing the earth for a few years.
If you burn every few years and/or clear the deadfall it doesn't tend to have the opportunity to get hot enough or reach the tree-tops and kill every single spruce/pine tree in the forest; they drop their cones (heat activated!) and new baby trees sprout. The forest recovers fairly quickly.
I'm not forest manager/firefighter guy, but that's my understanding.
The philosophical angle to all this is thus; Leave No Trace is great in areas that are well trafficked or where heavy impacts are easy to generate (OHV, for example *can* tear the land up if one doesn't use care), since the resources there are prone to destruction by sheer volume. It's nevertheless a product of urban romanticism and doesn't reflect the reality of most real wildland areas, especially if you're travelling in a non-motorized manner. Realistically, if I bring a chainsaw in to clear some deadfall for my fire, I'm probably doing more good than evil in the grand scheme of forest ecology. The LNT types that see nature as somehow distinct from humanity, who are largely urban professionals and not people who actually live or work close to the wild, don't seem to understand these sorts of relationships.