Mountain Pine Beetle

Adult Dendroctonus

Mountain pine beetles (MPB) are the most important insect pest of Colorado’s pine forests.

MPB often kill large numbers of trees annually during outbreaks. Trees that are not growing vigorously due to old age, crowding, poor growing conditions, drought, fire or mechanical damage, root disease and other causes are most likely to be attacked.

Mountain pine beetles develop in pines, particularly Ponderosa, Lodgepole, Scotch and Limber pine. Bristlecone and Pinyon pine are less commonly attacked.

During early stages of an outbreak, attacks are limited largely to trees under stress from injury, poor site conditions, fire damage, overcrowding, root disease or old age.

As beetle populations increase, MPB attacks may involve most large trees in the outbreak area.

Signs of MPB attack include:

	Popcorn-shaped masses of resin, called “pitch tubes,” on the trunk where beetle tunneling begins. Pitch tubes may be brown, pink or white.
	Boring dust in bark crevices and on the ground immediately adjacent to the tree base.
	Evidence of woodpecker feeding on trunk. Patches of bark are removed and bark flakes lie on the ground or snow below tree.
	Foliage turning yellowish to reddish throughout the entire tree crown. This usually occurs eight to 10 months after a successful MPB attack.
	Presence of live MPB (eggs, larvae, pupae and/or adults) as well as galleries under bark. This is the most certain indicator of infestation. A hatchet for removal of bark is needed to check trees correctly.
	Bluestained sapwood. Check at more than one point around the tree’s circumference.