-Spruce beetles (Dendroctonus rufipennis) are native bark beetles that infest Engelmann spruce (Picea engelmannii) and occasionally Colorado blue spruce (P. pungens) in high elevation forests in Colorado. The spruce beetle typically completes a generation in one to three years, with a two-year life cycle being the most common in spruce trees growing above 9,000 feet. Adults fly to seek new hosts in late May through July, preferring large diameter trees until they are depleted from the forest.
Signs & Symptoms
Needles on infested trees may turn a pale yellowish-green color and tend to drop to the ground after high winds, but rarely turn rust colored on the tree. Needles typically drop from branches the second summer after the tree has been infested. Boring dust, produced when beetles bore new entry holes, may accumulate in bark crevices and around the base of the tree.
Streams of resin along the main trunk are often associated with recently attacked trees.
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.
Outbreaks continued in portions of the San Juan/La Garita Ranges, West Elk Mountains, Sawatch Range, Sangre de Cristo Range and Wet Mountains. Significant infestations were also mapped in portions of Grand and Larimer counties in north-central Colorado, west of the Continental Divide in and around Rocky Mountain National Park.
206,000 acres of Engelmann spruce forests were impacted in 2017, compared with 350,000 acres in 2016.
67,000 new, previously uninfested acres were impacted statewide in 2017.