How do pine bark beetles kill trees?
Pine bark beetles (Ips sp. and Dendroctonus sp.) feed primarily on the inner bark (phloem tissue). This has the same effect as girdling (peeling off the bark to exposed wood) of the tree. Damage caused by their feeding acts as an internal tourniquet cutting off the flow of nutrients from the leaves to the other parts of the tree. As the damage progresses, sugars and other complex compounds cannot be translocated downward from the leaves to non-photosynthetic areas of the tree. The beetle can also introduces a blue stain fungus which grows into the wood (xylem). This fungus prevents water from being transported upward to the leaves. Both of these factors contribute to the decline and death of colonized trees.
