The wood-accented room was full. Adults of all ages sat in rows from wall to wall, filling the space from the lit projector screen in front to the conference table in the back at the Aspen Center for Environmental Studies’ Hallam Lake location. Dr. Dan West of Colorado State University (CSU) and the Colorado State Forest Service (CSFS) stood at the front, preparing to give a presentation on forest health and Douglas fir beetles.
West made the trip from Fort Collins to deliver the final presentation of the 2026 Naturalist Nights speaker series, hosted initially by Wilderness Workshop in Carbondale on Wednesday, March 4, then Hallam Lake that Thursday. The presentation was grounded in the local landscape. West and his CSFS research team work in the Roaring Fork Watershed annually, managing forest health and insect impacts.
West, who holds a Ph.D. in entomology, started by sharing facts about tree health and basic information on how beetles use trees as habitat. He reminded attendees that the water trees draw from the ground depends on precipitation. Therefore, drought and other weather patterns affect how much resin trees are able to produce. Resin acts as a sort of immune system. The sticky substance allows trees to close wounds and transport compounds that help deter insects. This is crucial, as West’s team has observed that over 90% of tree mortality is due to damage from bark beetles.
Douglas fir beetles (Dendroctonus pseudotsugae [Hopkins]) are named for the trees they rely on for habitat and food. West referred to them interchangeably as fir beetles and dendroctos. Female beetles can locate weak and sick trees due to unhealthy trees releasing chemical smells like ethanol or alcohol. Once female beetles have colonized a tree, other beetles track aggregation pheromones and join in. From there, more and more congregate and expand to neighboring trees.
Fir beetles lay eggs vertically in the bark of trees, with females channeling up under the bark surface while male beetles guard the entry point. When the larvae emerge, they eat the phloem of the tree, the water channel below the bark. But beetle larvae, unlike adults, move laterally through the phloem. The resulting scarring cuts off the water flow of a targeted tree, which girdles it and produces the red coloration associated with beetle kill as the tree dies.
“It’s harder and harder to be a tree in Colorado, because of higher temperatures and less water,” West said. He pointed out that increasing average temperature lows is a factor. In the past, low winter temperatures could kill bark beetles. But temperatures below the surface of the bark that eliminate the insect start at negative 35 degrees Fahrenheit. Temperatures that low almost never occur in Colorado anymore.
During a drought it is more difficult for trees to use resin as a defense. With adequate water, trees produce a strong resin that is toxic to adult beetles and their larvae. Trees in drought may not have the water to spare. Fire also kills beetles and removes unhealthy trees, but fires during drought are more dangerous.
“In the absence of fire or removal, we have an ever-growing quantity of fuel,” West emphasized.
He reminded the audience that bark beetles serve an important ecosystem role by thinning forests, and that the goal is not complete eradication of the insects. “There’s a lot of benefits to small, localized outbreaks of bark beetles,” West said.
CSFS scientists are not addressing healthy forests, but managing stressed ones. “We just don’t want beetles gone wild,” West quipped.
He explained how scientists use small planes and trucks to record visually-detectable insect and disease signatures in forests. He added that this work is done by people and, so far, not replicable by drones. West noted that in 2025, aerial survey was not possible due to red tape and budget restrictions brought on by the federal government.
Fir beetle damage tends to spread in dots within a forest, unlike the uniform wave observed when pine beetles spread through an ecosystem. This is, in part, because colonies of Douglas fir beetles select one host tree every year. West explained that the Roaring Fork Valley has been dealing with fir beetle damage for at least a decade.
West and colleagues have treated 185 to 200 acres each year with chemicals that send a signal to the beetles that the tree is full. They also deploy chemical pheromone traps to lure beetles from forests to open meadows. Elevations most affected by fir beetles are between 8,200 and 9,500 feet. CSFS teams have deployed treatments in forests around the Roaring Fork Valley within that elevation range.
Beetle numbers have been lower in the Valley in the past few years, suggesting that these treatment methods are effective. West said that this summer will likely be a valuable indicator of how well mitigation is working, given the current drought.
More information about fir beetles, pine beetles and other forest management topics can be found at csfs.colostate.edu