 Mountain pine beetle is a small but mighty insect that kills trees across the western United States. As the name suggests, mountain pine beetle targets pine trees such as lodgepole, scotch, and limber. Mountain pine beetles target large diameter green trees that have been injured or stressed. Under epidemic populations, they are less selective. Beetles commonly mass attack trees. The beetles tunnel into and under the bark and after they mate lay about 75 eggs. When the eggs hatch into larvae, they feed away from the egg gallery creating distinctive tunnels. Larvy overwinter onto the bark, transform into pupae in early summer and emerge from the trees in mid to late summer. At this time, they are looking for a new home. The pine trees try to put up a good defense when they are attacked. As the insect bores into the bark, the tree produces thick, sticky resin and attempts to push the beetle out of the hole. These pitch tubes are a sign of infestation. Pine beetles kill the tree by attacking in high numbers. The tunnels girdle the tree, stopping water and nutrient flow. They also carry blue stain fungus which is injected into the tree, clogging pores and accelerating its demise. Trees die within a few weeks of attack, but the needles take a year to turn red and three to four years to drop. From the University of Wyoming Extension, I'm Mae Smith, Exploring the Nature of Wyoming.