-Mountain pine beetles (Dendroctonus ponderosae; MPB) are native Colorado bark beetles that predominately infest ponderosa pine (Pinus ponderosa), lodgepole pine (P. contorta), and limber pine (P. flexilis). However, numerous species of pines, and all pines found in Colorado are susceptible when beetle populations explode, including ornamental pines.
MPB complete a generation within one year from egg to adult. Adults typically fly to seek new hosts in July through August, though a small proportion emerge earlier and some later through the summer months. Attacking females initially prefer large diameter trees until they are depleted from the forest.
Signs & Symptoms
Needles on infested trees typically turn ‘rust’ colored on the tree after a short period of yellowish-red and typically drop from branches the second summer after the tree has been infested. Boring dust in bark crevices and on the ground immediately adjacent to the tree base are also a sign of bark beetles.
Often popcorn-shaped masses of resin, called “pitch tubes,” are found on the trunk where beetle tunneling begins. Pitch tubes may be brown, pink or white. Woodpecker damage, where the birds have stripped portions of the bark from infested trees in search of larvae, leaving accumulations of bark at the base of trees is often an indicator of bark beetle presence. Exit holes on the bark surface may be seen after the adult beetles emerge from infested trees.
MPB impacted nearly 3.4 million acres in the state from 1996 to 2014, but populations now remain at endemic, or background, levels statewide. Infestations in both ponderosa and limber pines continued at moderate to low levels in the northern and central Sangre de Cristo Mountains. Localized “pocket” activity also occurred in ponderosa and lodgepole pines throughout the Front Range, although the causal agent for visible damage might include other native bark beetles.
Less than 900 acres of native pine forest was affected by MPB in 2017, which is similar to the acreage affected in 2016.
2017 represents the year with the lowest acreage impacted by MPB in more than two decades.