Mountain Pine Beetle
Mountain pine beetle (MPB) is an insect native to the forests of western North America and is also known as the Black Hills beetle or the Rocky Mountain pine beetle. MPB primarily develop in pines such as lodgepole, ponderosa, Scotch and limber pines, and less commonly affect bristlecone and piñon pines.
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.
Annual Insect Activity
CSFS Forest Entomologist Dr. Dan West produces an Esri Story Map for the Annual Forest Health Report, which offers users an interactive way to find out about forest conditions and insect activity in their area.
Large outbreaks of bark beetles are difficult to control. One of the best ways to mitigate the effects of beetle outbreaks is to manage for overall forest health and resiliency. Thinning overly dense stands of trees to reduce competition and promote tree age and species diversity is the most successful forest management strategy to promote tree vigor. Small infestations can be eliminated by quick action by removal of infested trees.
Options for management include:
- Remove infested trees and slash from thinning or pruning. Continual removal of trees already affected by other insects or affected by diseases, overly dense treed areas, should be prioritized as these trees and areas are most frequently attacked.
- Solar treatments can be used to reduce mountain pine beetle populations in small infested stands. These treatments involve felling infested trees and stacking cut logs in an area with full sun before covering them with clear plastic. The solar treatment of infested trees creates conditions unsuitable for survival of mountain pine beetle larvae.
- Trap trees serve as traps for recently emerged, adult beetles. After the trap trees become infested with beetles, trees are removed and destroyed, usually during the fall or winter, while all of the beetles are still inside.
- The use of pheromone packets containing verbenone may disrupt the attraction of incoming beetles and can be used to reduce attacks on pine trees where no other management options are effective (e.g. in close proximity to water, near structures where overspray of preventive insecticides may be undesirable.) The effectiveness of verbenone has much been debated in the scientific literature. Consult your local field office for more detailed information on using pheromone applications.
- The use of preventive insecticide sprays may prove effective in preventing mountain pine beetle infestation. Certain formulations of pyrethroids that are registered and tested for effectiveness are the primary preventive insecticidal sprays used to help reduce the likelihood of attacks on individual trees. The Colorado State Forest Service recommends spraying only high-value trees, such as those near homes, businesses or recreation sites. Follow the label of any chosen product.
Mountain Pine Beetle (362 KB PDF)
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.