Insect Blog

Mountain Pine Beetle

May 14th, 2019

Trees Affected:

Ponderosa, Lodgepole, and Scotch Pines.


This insect causes small globs of pitch to form around small holes in the trunk or in branches over 6” in diameter.  The tree may start fading or browning and inspection by cutting into the tree may reveal a blue/gray staining of the wood.

Description/Life Cycle:

Eggs are laid by beetles inside the bark in August.  These eggs hatch and overwinter as small white grubs.  The following year they emerge as small, dull-black beetles and fly to other trees from June until August, at which time they bore into trees and lay eggs, and the cycle repeats itself.


May introduce a disease called Blue Stain fungus into the tree, which is incurable.  Controls are therefore aimed at stopping the beetle before it infects the tree.  It is beneficial to reduce any other stresses to the tree where possible.  A bark treatment is timed to coincide with the emergence and flight of the beetle to other trees.  Balanced deep root fertilization to invigorate the tree is also recommended.