Pine Beetle FAQ

Do mountain pine beetles eat wood?

Pine beetles eat the cambium layer (phloem) of the tree, which is considered to be wood. The cambium layer is what carries nutrients and water throughout the tree. If it is severely damaged by pine beetles, the tree can’t survive.

How do the mountain pine beetles kill the trees?

Pine beetles bore through the bark into the phloem layer of the tree, on which they feed and into which they lay their eggs. Pioneer female beetles initiate the attack, and produce pheromones which attract other beetles and results in mass attack. The trees respond to attacks by increasing their resin output in order to discourage or kill the beetles.

It isn’t the number of pitch tubes that kill the tree, but the fungus carried by the beetles that stain the wood blue. This fungus blocks the tree’s resin response, preventing it from pitching out the beetles. Usually within two weeks of a beetle attack, the tree becomes overwhelmed as the phloem layer becomes so damaged that the flow of water and nutrients is cut off and the tree starves to death. The needles turn red from lack of nutrients, and you will see entire groves of trees after an outbreak appear reddish for this reason. After particularly long and hot summers, the mountain pine beetle population can increase dramatically, which leads to the deforestation of large areas.

Are my smaller trees at risk?

Although older trees typically succumb to pine beetles first, smaller trees are also at risk. Beetles usually select larger trees that have thick phloem, because they need this food supply to build up their population. After they kill the larger trees by consuming the phloem, beetles infest smaller and smaller trees. As the pine beetle epidemic progresses, we are seeing beetles in trees as small as 2.3 inches in diameter at chest height.

Does preventive spraying work?

Spraying can be very effective if implemented correctly. We average 99% effectiveness with our spraying efforts; however, heavily infested areas in unhealthy forest stands may experience a lower level of effectiveness. Spraying sometimes receives a poor report, generally because of improper applications usually implemented by unqualified applicators, but we fully endorse it. Learn more about tree spraying from TigerTree.

When should I spray?

The sooner the better. The earlier in the year you spray, the sooner you will be protected against beetles that take flight prematurely. Our spray season starts in April and goes through July. We also recommend spraying earlier to prevent disturbing beneficial bugs.

For how long should I spray?

You will need to spray every year for as long as the pine beetle epidemic lasts. In some areas hard hit by the mountain pine beetle epidemic, this could only be for two more years. In some areas recently experiencing the mountain pine beetle epidemic, you should continue spraying for 5, 7 or 10 years, depending on the rate of spread for the geographical area in which you live.

How do I know if a tree company is doing its job correctly?

You should make sure that the insecticide applicator:

  • Sprays from ground level to the point where the tree tapers to less than four inches.
  • Sprays around the entire circumference of the tree and does not miss areas with large branches or forks. Otherwise, the unsprayed “windows” are open to attack.
  • Does not spray trees if there is a chance it may rain within two hours after application. Once the insecticide dries on the tree bark, it will be resistant to wash-off.
  • Uses a chemical that is specifically labeled for mountain pine beetle. It needs to have the right additives to bind the active ingredient to the bark.

I scheduled with TigerTree. Why haven’t you sprayed yet?

One word – weather! We can only spray when there is no water on the ground in any form, including snow, hail, puddles, etc. because we don’t want to contaminate any water – our insecticide is extremely toxic to fish. We can also spray only when there is limited wind. That leaves us at the mercy of Mother Nature herself. If you scheduled with us, we will be there when time allows.

What is a sticker?

A sticker or spreader is a combination of two adjuvants, which are materials added to spray mixtures to increase the effectiveness of the main active ingredient. If we want to be completely correct with our terminology, we probably ought to note, too, that stickers or spreaders are adjuvant surfactants. Surfactants are adjuvants that reduce surface tensions of solutions, helping them spread and cover leaves more efficiently.

What is the life cycle of the pine beetle?

Mountain pine beetles have a one-year life cycle that begins with the flying and infesting of new trees between early July and late September. Beetles bore into a tree, lay their eggs under the bark, and then die. The eggs hatch into larva in late fall and begin feeding inside the tree.  The larva produce an alcohol called glycerol that acts as antifreeze, protecting them during the cold winter months.  They feed during the winter and spring months on the tree’s phloem layer, located under the bark of the tree. The phloem acts as the tree’s veins that carry water and nutrients up to the top of the tree.  The larva disturb this flow, effectively girdling and killing the tree.  Then the larva pupate in early summer and emerge as adult beetles in midsummer, starting the cycle over. The spread rate from summer to summer during the current epidemic levels can range from 5 to 50 new infestations each year.


Which trees are susceptible to bark beetles?

Many tree types are susceptible to mountain pine beetle or other species-specific bark beetles, such as spruce bark beetle and Douglas-fir beetle.  We have seen a spread of bark beetle attacks in the following tree types:

  • All pine species, including Lodgepole, Ponderosa, Limber, Austrian, Scots, Whitebark, Pinyon, and bristlecone
  • All spruce species, including Blue, Green, and Engelmann
  • All fir species, including Douglas-fir, Subalpine, White, and Concord
  • All elm trees

Mountain pine beetles historically have attacked larger diameter, older trees.  The old standard for the minimum size that the pine beetles prefer to infest has been eight inches in diameter at breast height (DBH).  In the current epidemic, this standard has proven to be inaccurate.  The minimum susceptible diameter depends on the level of infestation and the overall forest health.  In overcrowded forests experiencing a high infestation rate, we are seeing pine beetles in trees down to two inches DBH.

The main factor that affects pine beetle infestation rates is the health of the trees, which is related to available moisture, nutrients and sunlight. The main cause of tree stress stems from competition among trees in overcrowded forests, but they may also become stressed and weakened because of drought and poor soil.

Because unhealthy trees release a stress signal that attracts pine beetles, the beetles are attracted to areas where the basal area is too high, which means the tree mass is too high per acre. When areas have too much mass for a given amount of water and nutrients, the trees become weak.  Contact us to have the basal area of your forested property calculated to help determine the susceptibility of your trees to pine beetle attacks.

Over Thick

Is the fight against the mountain pine beetle worth engaging?

It sometimes feels like we are all losing the battle against the pine beetle. Mountainsides have been left dead from this insect in the past years. However, treatments are working very well in areas where property owners are being proactive. One benefit that is stemming from this epidemic is increased awareness of the need for proper forest management. While we will not be able to save every tree from this insect, through a variety of proactive treatments we can strengthen the forests for a natural fight against future forest ailments.

Can I burn infested trees to kill the beetles?

Burning trees currently infested with beetles definitely kills the beetles in the tree. However, most currently infested trees are too green to burn effectively. This dilemma has encouraged the introduction of air curtain burners, which are incinerators that reach a high enough temperature with the help of forced air to effectively burn green trees. Many local municipalities are encouraging this safe and effective practice by providing an incinerator for public use. Contact us to find out where the closest air curtain burner is to your location.

How cold is cold enough to reduce beetle populations?

The most recent studies suggest that sustained temperatures of -40 degrees F are required to have any effect on beetle populations. The beetles metabolize an alcohol called glycerol inside the tree that acts as antifreeze, protecting them during the colder winter months.

Is wrapping infested trees in plastic effective?

One question we receive every day is whether wrapping trees in plastic to “cook” the beetles is working.  Our experience has shown this method of killing beetles has limited effectiveness.  We have removed many infested trees directly adjacent to these wrapped piles.  The idea is sound, but reaching a high enough temperature inside the plastic requires many days of direct sunlight and much work continuously rotating the wood inside the plastic.  Many homeowners are experimenting with small wood ovens that they are using to “cook” the beetles with the aid of a wood-fired stove.  The initial testing of this method has proven to be more successful.  Our recommendation is still to chip an entire infested tree.

Is this current mountain pine beetle epidemic natural?

Mountain pine beetles, along with other species of bark beetles, are a natural part of a healthy forest ecosystem.  However, the current pine beetle epidemic is on a scale that has not been recorded in recent history and we are continually surprised at the spread rates we are seeing every year.  There are many ideas regarding what has brought this infestation to the current epidemic level, including poor forest management, drought, and global climate change.  Whatever the cause, proper forest management can strengthen the trees against future insect, disease, and wildfire outbreaks.

What is the minimum size tree that beetles will attack?

The standards for size and species of trees that are being infested are continually changing. We have seen mountain pine beetles infest trees down to two inches diameter at breast height. Many municipalities are seeing pine beetles infest other conifer species such as spruce and fir as well, but the trees being killed in these attacks are from the blue stain fungus that is introduced along with the beetle. Whether or not the beetles are successfully reproducing in these different species has yet to be seen. There are also different bark beetle species that are infesting these other conifer species as well.