Cut tree killed by MPB, showing the characteristic bluestaining pattern. MPB larvae spend the winter under the bark. They continue to feed in the spring and transform into pupae in June and July. Emergence of new adults can begin in early July and continue through September. Spores of these fungi contaminate the bodies of adult beetles and are introduced into the tree during attack.
Fungi grow within the tree and, together with bark beetle feeding, weaken it.
This mutual network of beetle galleries and bluestain fungi disrupts the movement of water within the tree and rapidly kills it. The fungi give a blue-gray appearance to the sapwood. Once MPB infest a tree, nothing practical can be done to save that tree. Under epidemic or outbreak conditions, enough beetles can emerge from an infested tree to kill about two same-sized trees the following year. The direction and spread rate of a beetle infestation is impossible to predict.