According to an article appearing in the April 2015 issue of National Geographic, more than 60 million acres of forest — from northern New Mexico through British Columbia — have suffered die-offs since the 1990s due to the spread of the mountain pine beetle (Dendroctonus ponderosae).
The beetles bore through the bark and create tunnels beneath it, where the females lay eggs. When the eggs hatch, the larvae feed on the bark as well.
But it gets worse. The beetles are fungus farmers that carry spores on their bodies. When they tunnel under the bark, the spores grow, providing an excellent food source for pine beetle larvae — but it simultaneously damages the trees, including lodgepoles, ponderosas, white pines, jack pines, and others.