The Mountain Pine Beetle is a bark beetle that destroys the cambium and introduces the blue stain fungus in Ponderosa, Lodgepole, Scotch and Limber pine trees. It is fatal to most trees when attacks are successful.
The beetle itself is small, about 1/8 to 1/3″ in length, and brown to black in color. They have wings as adults and fly from tree to tree. The noticeable symptom is the pine tree turns brown. Upon closer examination, the browning tree will have “popcorn-like” yellow mounds of sap jutting from the trees bark. These are also called “hits” or “pitch tubes.” The tree is literally pitching the beetles out using sap that flows out profusely when the cambium is damaged.
Luckily the population of this insect has declined over the years. However, if you do see any evidence you'll want to take immediate action to help protect your trees. There are multiple treatment options that can be used, it's best to contact a certified arborist to have then help outline your options.