Coordinated mass attacks by many beetles are common. 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 the tree.
This mutual network of beetle galleries and bluestain fungi disrupt transport of water in the tree and rapidly kill it. The fungus gives a blue-gray appearance to the sapwood.