I believe they are native, but that fire, rain and brutal winter usually keep them in check. Drought is a huge concern too, the more sap a tree has in its 'veins' the harder it is for the beetle to do its thing. Healthier trees fight them off. Young trees thus don't generally have that problem. there is already a bumper crop of 4 to ten foot trees underneath that brown canopy in places, with a lot of grass in places there never was. Good for the critters, it adds security and food. Plagues like this hit randomly occasionally. I think its been about 25 or 30 years they said since one this bad has been in North America.
However, we don't have regular wildfires anymore, they get put put.