Experts expect a red, rusty hue to take over pine trees this summer as mountain pine beetle infestations resurge, threatening trees in Front Range communities, including the Estes Valley.
As the beetles make their return, both residents and state officials are preparing for the challenges ahead.
Dan West, Colorado’s state forest entomologist, said mountain pine beetle outbreaks kill trees on a massive scale, reshape wildfire behavior and water systems, drive up costs for communities, and permanently alter forest landscapes.
Scott Stewart, a resident of the Little Valley neighborhood southeast of Estes Park, pointed out an infested ponderosa pine tree during an interview with the Estes Valley Voice. Stewart described the beetles as spreading as quickly as the flu, and he pointed out small resin clumps called pitch tubes on a tree’s trunk.
“It only takes one tree, or somebody gets firewood from someplace that’s infected, all those beetles could come out of that firewood and start a whole new infection,” Stewart said. “Next thing you know, it’s in 20. And then after that, it’s in 100.”
Stewart emphasized the importance of acting quickly once there are signs of infestation, by removing infected trees and, where there is an immediate nearby threat, spraying healthy ones with insecticide to limit further spread.
“People come here for recreation because it’s beautiful,” Stewart said. “When all the trees are dead, it does come back, there’s a lot of seeds out there, but it’s different.”
A fact sheet available on the Colorado State Forest Service website reports that mountain pine beetles, or bark beetles, most commonly develop in ponderosa, lodgepole, scotch, and limber pine trees. Infestations are equally evident in wilderness areas, mountain subdivisions, and backyards.
The State Forest Service’s mountain pine beetle page explains that bark beetles have a one-year life cycle. In the fall and winter, eggs hatch and larvae grow under the bark. In late winter and spring, larvae complete their growth and pupate. In summer, new adults emerge to seek green trees and lay eggs.
West said the beetles that will emerge this summer are “already baked in” — the adults were laid last year, so their numbers are essentially set. The native mountain pine beetles drive the forest’s natural sanitation and renewal processes.
“These bark beetles are always going to be here,” West told the Estes Valley Voice. “Our forests have evolved and co‑evolved with these bark beetles. They are the sanitizers of our forest.”
But recently, years of warming, drier seasons, and over-dense, fire-suppressed forests have tipped the balance in the beetles’ favor. This environmental shift has contributed to the ongoing outbreak and increased risks to forest health.
The mountain pine beetles affected 3.4 million acres of Colorado forests from the late 1990s to 2013, killing 80 to 90 percent of trees in some lodgepole pine forests, according to the State Forest Service. In the early 2010s, they attacked ponderosa pine trees along the Front Range. Heavy rain in 2013 ended the epidemic.
West explained that trees use water to create resin, which can form pitch tubes — small, gumball‑like blobs of resin on a pine’s bark where a bark beetle has tried to bore in. The tree pushes out resin through its “garden hose”‑like ducts to defend itself.
“Trees defend themselves against bark beetle attacks through water,” West said. “They turn that water into resin. In the absence of this resin, or very little of this resin, there’s very little defense in the trees.”
Mountain pine beetle larvae also cannot survive temperatures below 30 degrees Fahrenheit if maintained for five consecutive days. Because recent winters have reached those temperatures less frequently, more larvae are reaching adulthood.
“Bark beetles used to have a small proportion of their population die off over the winter, because it became so cool they just simply couldn’t make it,” West said. “But we just simply don’t have those super cold winters anymore…We no longer calculate that into any algorithm.”
Know the signs of a mountain pine beetle infestation
The State Forest Service advises landowners to inspect properties, mark infested trees, and plan removals. West said spring is the best time to check for infestations and apply measures before beetles emerge. The State Forest Service outlines these signs of infestation:
- Popcorn-shaped masses of brown, pink, or white resin on the trunk
- Foliage turning yellowish to reddish throughout the entire crown of the tree, which usually occurs eight to 10 months after a successful attack
- Boring dust in bark crevices and on the ground next to the tree’s base
- Exit holes on the bark surface where adult beetles have emerged
- Woodpecker damage (where the birds have stripped portions of the bark in search of larvae), leaving accumulations of bark at the base of the tree
- The presence of live mountain pine beetle eggs, larvae, pupae, and/or adults
Mountain pine beetle mitigation tactics are both curative and preventative
The State Forest Service takes a multi-pronged approach to mitigating bark beetles, including individual tree treatments, forest management, and community involvement, according to West. He said that working with clients ranging from individual homeowners to entire counties requires different management approaches, and that these tools can be used in tandem as needed.
“It’s not just one silver bullet,” West said. “It depends on who we’re working with…Literally, each project is slightly different in scope, scale, and the objectives based on the services that we’re looking to get out of it.”
West highlights preventive measures, such as applying insecticide sprays to at-risk trees and intentionally seeking out infested trees to remove them before the beetles can spread.
The State Forest Service’s mountain pine beetle page notes that removing infested trees can stop small outbreaks, but larger infestations are harder to control.
West said that one method is thinning forests: With fewer trees competing for water and other resources, the remaining trees stay healthier and are better able to defend themselves against bark beetles.
He also said they use pheromones as a management tool, deploying baited funnel traps in nearby meadows to catch flying bark beetles and, in some cases, cutting and baiting “trap trees,” or logs that draw beetles in and are then hauled away and chipped to destroy the insects inside.
Additionally, West said they can use anti‑aggregation pheromones, placing packets of a compound called verbenone on selected trees to mimic the beetles’ own “no vacancy” signal and push new beetles to fly past those trees in search of other hosts.
West said he believes that forests should be treated as infrastructure. He highlights education as a proactive tool and encourages people to work together — neighbors, communities, and local governments — to tackle the problem at a meaningful scale.
Stewart said that if neighbors don’t act, everyone around them is at greater risk.
“It takes a community-wide effort for it to work,” Stewart said. “You can spray your own trees, and you can be an island, but everything around you is ugly, and all of a sudden you went from having, maybe privacy and not seeing your neighbor, to feeling like they’re practically living next door to you, because there’s no trees left.”