Rocky Mountain Pine Beetle: 13 Things (2024) You Ought to Know

Have you heard about the mountain pine beetle epidemic occurring in Rocky Mountain National Park?

This beetle is aggressive and devastating to the forests it invades.

It kills timber at a 70 to 90 percent rate.

If you think the mountain pine beetle isn’t impacting the area where you live, think again!

Here’s what you should know about it.

1. What is the mountain pine beetle?

The mountain pine beetle (dendroctonus ponderosae) is a species of bark beetle native to western North America.

You may also hear it called the Black Hills beetle or the Rocky Mountain pine beetle.

2. What are the signs and symptoms of the mountain pine beetle?

When a tree has been infested, the needles will typically turn rust-colored after a short period of yellowish-red and drop from branches the second summer after the infestation.

Boring dust in bark crevices as well as on the ground near the tree base are also signs of bark beetles.

You can also find “pitch tubes” — popcorn-shaped masses of resin — on the truck where beetle tunneling begins.

These tubes may be brown, pink, or white.

You may also see woodpecker damage where birds have stripped portions of the bark from the infested trees.

They do this because they are searching for larvae to eat.

They leave behind accumulations of bark at the base of the tree.

Looking for this bark is a great indicator that bark beetles are present.

Yet another sign is exit holes on the bark surface.

These can be seen after the adult beetles emerge from the trees.

3. What is the host tree species of the mountain pine beetle?

The mountain pine beetle predominantly infests the ponderosa pine, lodgepole pine, limber pine, Western white, and whitebark.

That said, numerous other species of pine as well as all pines in Colorado are susceptible when beetle populations get to overwhelming numbers (even ornamental pines).

Generally speaking, mountain pine beetles prefer to attack larger, more mature trees.

Those that are 80+ years old are more susceptible to attack.

4. What is the life cycle of the mountain pine beetle?

Rocky Mountain pine beetles develop through four stages.

  1. Egg
  2. Larva
  3. Pupa
  4. Adult

Almost all life stages are spent beneath the bark of brood trees.

The exception is a few days during the summer when adult beetles emerge and fly to attack new host trees.

Female beetles initiate these attacks by releasing pheromones which help attract males.

Together, they’ll chew into the inner bark and phloem.

Eventually, more pheromones will be released, which results in a mass attack that overcomes the tree’s defenses.

Once one tree is attacked, the beetles will turn to adjacent trees.

In general, mountain pine beetles require a single year to complete the life cycle.

Although, at higher elevations where the temps are cooler, the life cycles can sometimes vary between one to two years.

5. How do mountain pine beetles infest trees?

Mountain pine beetles infest pine trees by laying eggs under the bark.

They also deposit blue stain fungus into the sapwood that prevents the tree from repelling and killing the attacking beetles with tree pitch flow.

This fungus also blocks water and nutrient transport inside the tree.

On the tree’s exterior, the fungus results in popcorn-shaped masses of resin called pitch tubes where the mountain pine beetles have entered.

This is a tell-tale sign that the tree is infested.

Within a few weeks, the larval feeding and the fungal colonization kill the host tree.

Drought conditions have also contributed to the rising rate of infestation.

Pine trees are now much more vulnerable to attack from pine beetles, and the trees are even more unable to defend themselves against attack.

You typically cannot spot the infestation of a tree based on color alone immediately.

In the first year of the attack, the tree’s needles will remain green.

After that, the needles will turn red which means the tree is either dead already or dying.

At this point, the beetles have likely moved on to another tree.

After three to four years of attack, the tree will appear gray.

6. Who are the natural predators of the mountain pine beetle?

The natural predators of the mountain pine beetle include certain birds, particularly woodpeckers, and various insects.

7. What are the best management techniques for mountain pine beetles?

Since the mountain pine beetle is an invasive species, it’s important to have management techniques that help to keep them in check and protect our forests.

Here are the management techniques that can be used to manage infestations.

bulletSelective harvesting

Thinning and removing impacted trees at the leading edges of what’s known as the “green attack” can be an effective management technique for larger infestations.

Trees that are impacted by other insects or diseased should also be removed because these are often the ones that are frequently attacked.

The same goes for trees in overly dense areas.

bulletPheromone baiting

This technique helps to lure beetles into trees that are baited with a synthetic hormone.

This mimics the scent of a female beetle.

Once the beetles are contained in a single area, they can be more easily destroyed.

bulletSanitation harvesting

This technique removes single-infested trees to control the spread of beetle populations to other areas.

bulletSnip and skid

This method involves removing groups of infested trees that are scattered over a large area.

bulletControlled (or mosaic) burning

For this method, you burn an area where infested trees are concentrated to help reduce high beetle infestations.

It can also reduce fire hazards in the area.

Because firefighting technology has improved, controlled wildfires have increased in use since the 1980s and 1990s.

bulletFall and burn

This technique involves cutting down beetle-infested trees and then burning them to prevent the spread of beetle populations to other areas.

This is normally done in the winter to reduce the risk of starting forest fires.


Pesticides are also used to help contain the mountain pine beetle population.

The most common pesticides used in smaller area applications are carbaryl, permethrin, and bifenthrin.

Biopesticides like chitosan have also been tested for protection.

Scientists and the United States Forest Service are constantly seeking new natural plant defenses in the hopes of eliminating the mountain pine beetle infestation.

Currently, microbial solutions are being researched and developed.

These defenses will hopefully work with the plant to activate and enhance its resistance mechanisms against insects and disease.

bulletSolar treatments

Solar treatments are also used to reduce the pine beetle population in small, infested stands.

These treatments involve cutting down infested trees and stacking the logs in areas with full sun.

After this, they’re covered with clear plastic.

This creates an environment unsuitable for mountain pine beetle larvae, and as a result, they’re destroyed.

bulletTrap trees

Recently emerged, adult beetles can get caught in trap trees.

After the beetles are stuck, the trees are removed and destroyed.

This normally occurs during the fall or winter when the insects are still inside.

8. What’s the best way to slow the spread of mountain pine beetles?

The best way to slow the spread is to aggressively search out, remove, and destroy the brood in infested trees.

However, this technique may not protect specific trees.

When possible, we should spray trees to prevent an attack in the first place.

Spraying them in advance can protect a small number of high-value trees from mountain pine beetles.

The best pesticides to spray include carbaryl, permethrin, and bifenthrin.

They’re currently registered in the U.S. for use in the prevention of pine beetle infestations.

9. What are the best pesticides to use?

The following pesticides are recommended by the U.S. in the prevention of pine beetles.

However, pesticides can be harmful to other organisms.

Here are the details of what you should know if you’re considering using one of these on your property.


As this is considered by the EPA to likely be carcinogenic to humans, this may not be the best option for trees that are on a property close to a residence.

Additionally, it’s moderately toxic to wild birds and partially to highly toxic to aquatic organisms.


This pesticide is easily metabolized in mammalian livers, which makes it less dangerous to humans.

Additionally, birds are almost entirely unaffected by permethrin.

Negative effects can be seen in aquatic ecosystems, and this pesticide can be very toxic to other beneficial insects.


Bifenthrin is a moderately dangerous pesticide to mammals (including humans).

Compared to permethrin, it’s slightly more toxic to birds and aquatic ecosystems.

While it’s effective against the mountain pine beetle, it’s extremely toxic to beneficial insects, which is good to keep in mind.

10. How do mountain pine beetles affect the commercial use of timber?

As noted above, mountain pine beetles infest trees.

If they reach trees that are intended to be used for commercial timber purposes, they can cause a variety of issues.

The most significant are quality and use.


Although wood from beetle-kill timber trees retains its commercial usefulness up to 8 to 12 years after the tree has died, its value drops within several months.

This is because escaping moisture causes cracks throughout the timber, and this creates difficulties for modern high-output automated sawmill operations, escalates the lumber losses, and increases the labor to produce high-quality wood products.

The “shelf-life” of timber is dependent on factors like economic and stand site conditions.

When conditions are wetter, the trees tend to rot at the base and fall faster (especially if they’re larger).

The fungus caused by the beetles also causes staining, but it doesn’t affect the wood’s strength or create human health effects.

That said, it’s considered a “down-grade” and results in a lower-commodity market price.


Timber is utilized for a variety of wood products, including standard framing lumber to engineered wood products (glue-laminated products or cross-laminated panels).

Unfortunately, while beetle-killed timber can still be utilized, there are very few companies that have created product lines that require dead timber in such a large volume.

That said, blue-stained pine is available in some big box stores like Lowe’s.

11. What has caused the recent beetle outbreak?

The mountain pine beetle epidemic has killed millions of acres of pine forests.

While Colorado is particularly vulnerable to these insects, the issue extends up as far as British Columbia.

This outbreak of mountain pine beetles is considered to be more extensive and severe than previous outbreaks observed throughout the 20th century.

The outbreak is due to a variety of factors — a perfect storm of conditions.

bulletSeveral years of warmer-than-normal winter temperatures have caused an increase in beetle populations

bulletA drought lowered the defenses of trees

bulletLarge expanses of lodgepole and other pine trees across North America reached the right age for beetle infestation (100 to 150 years old)

In general, both forest structure and climate played a role in the recent outbreak.

Depending on who you ask, they may tell you that one factor was more important than the other.

12. Do mountain pine beetles create a fire hazard?

There’s an enduring belief that beetle infestations and the trees that are killed as a result are going to prompt more forest fires.

However, this belief is currently being challenged.

Some studies (still ongoing) have demonstrated that beetle kill may reduce small fuels and thus limit the effect and reach of fires.

13. Is there anything else I should know?

bulletThe mountain pine beetle has now migrated well beyond its historic range.

It’s expanded into northern British Columbia and eastward into the boreal forest of north-central Alberta.

Since the early 90s, the mountain pine beetle has attacked 50 percent of the total volume of commercial lodgepole pine in British Columbia.

bulletWhen the beetle population is low, healthy trees can defend themselves.

They produce a toxic resin that allows them to suppress an attack.

Unfortunately, when more beetles come to a healthy tree, its natural defenses are overwhelmed.

bulletEpidemic population levels of the mountain pine beetle decline only when all large pine trees are dead or weakened.

bulletThe mountain pine beetle population is affected by the weather.

The beetle population grows when the summers are warm/dry and the winters are mild.

Final Thoughts

The mountain pine beetle is drastically damaging pines out West!

If they’ve hit your land, you know this epidemic is negatively impacting your trees.

Take action today with management techniques that can help slow and eliminate the spread.

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Erika Gokce Capital

Disclaimer: we are not lawyers, accountants, or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.


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