"Fieldnotes," January 26th & 27th, 2014: "Blue Stain and Beetles," by Richarda Ruffle.
http://www.montananaturalist.org/
"Elusive to the human observer, the mountain pine beetle lives its life under the bark of both living and dead trees. The only time it leaves the bark is when the adults are looking for a new tree to infest. The mountain pine beetle and the blue stain fungus are so closely linked that the beetle has special cases for its traveling companions inside its body. The fungus gets a safe, free flight to a tree, and an easy trip into the bark inside its winged and wood-boring host."