Bark Beetles


There are a large number of dead pine trees on the Coconino National Forest and around the City of Flagstaff. The majority of these trees have been attacked by beetles or have fallen victim to drought stress. Beetle infestation is enhanced when the insects attack drought stressed or fire stressed trees. Drought stressed trees can easily die from beetle infestation because they cannot produce enough pitch to protect themselves from the insects.

           photo showing two bark beetles and a scale                                  

There are several methods that may help protect high-value trees on private property from beetle infestation, but landowners need to be aware that there are so many variables that influence beetle infestation, that treatment to these trees should be considered on a case-by-case basis.

The Coconino National Forest is focusing on improving the health of existing green stands of trees by reducing the density of trees back to a healthy level. Helpful information on bark beetles and treating trees on private property is available from the links below.



For more information on insects of the area, please visit these sites:



  • Much of Arizona is currently experiencing a large upswing in pinon and ponderosa pine mortality due to outbreaks of several species of Ips beetles and the western pine beetle.  Low tree vigor caused by several years of drought and excessively dense stands of trees have combined to allow beetle populations to reach outbreak levels.
  • These insects are native to ponderosa pine forests and pinon-juniper woodlands of the Southwest, and normally only attack a small number of diseased or weakened trees.  Healthy trees are usually not susceptible to these beetles.
  • The beetles are tiny, roughly 1/8 inch long, or about the size of a match-head.
    photo showing a bark beetle with a scale to indicate size  
  • These beetles have multiple generations per year, and they have a tremendous capacity to increase their populations.
  • The beetles attack trees by boring through the bark and laying eggs.  When the eggs hatch, the larvae feed on the soft inner bark.  Also, the beetles introduce a "blue-stain" fungus that spreads and clogs the water and nutrient conducting tissues and hastens tree death.  Once the insects mature, they leave the infested tree and travel to a new host.  Usually, they travel only a short distance, but they are capable of moving up to ½ mile or more.
  • Millions of ponderosa pine and pinon trees have been killed.  Overall, this equates to a loss of less than 2-3% of forests, although tree losses may be as high at 90% on some localized sites.  This is the largest bark beetle epidemic ever recorded in Arizona.  Many more trees are expected to die, especially if the drought persists.
  • Currently, most tree mortality is centered in "stress-zones" such as drier south-facing slopes, transition areas between ponderosa pine and pinon-juniper areas, recent construction sites, and areas heavily infected with dwarf mistletoe.
  • Infested trees will start to turn reddish-brown within a month of attack.  Evidence of infestation can include sawdust at the trees base or in bark crevices, small pop-corn like masses of sap ("pitch tubes"), small boring holes, and a "fading" of the needles.
  • Once beetles have left a tree, it no longer poses a threat to other trees as a source of beetle infestation.



  • There is nothing that can be done to save a tree after it has been successfully attacked by bark beetles and infected with the blue-stain fungus.  If the goal is to kill the beetles under the bark, then infested trees must be cut-down and treated by one of the following means:
    • Cover logs with clear plastic in a sunny site (this produces high temperatures by a greenhouse effect), ensure that the plastic remains intact, wind and ultraviolet damage can easily cause tears in the plastic and allow the beetles to escape.  Burry the edges of the plastic creating a tight seal around the infested wood.  Logs can be left uncovered in a sunny site but must be rolled weekly for even drying.
    • Peel the bark from logs, or
    • Burn, chip, or bury the logs.  (It must be noted that fresh pine chips can attract bark beetles and should not be left adjacent to standing green pines.)
  • Fresh pine debris over 4-inches in diameter, created during tree thinning operations, must be removed from the forest or treated, because it can serve as a breeding site for Ips beetles.

  • There is no effective insecticide treatment for infested trees.  Injecting trees with insecticides is not an effective method of control or prevention.

  • Due to the large extent of the outbreaks and the tremendous capacity of bark beetles to increase their numbers, there is no possibility of implementing effective control actions to prevent further tree losses on a landscape level.



  • Trees not yet infested can be protected by annual applications of a preventive insecticide. Carbaryl and permetherin-based insecticides are specifically labeled for this purpose, but carbaryl is the preferred material because it provides longer protection. Typical home and garden insecticides should not be used. The entire surface of the trunk and large limbs must be sprayed all the way to within a few feet of the top.
  • Watering individual trees can help increase a trees natural defense of pitching out attacking beetles.

  • Over the long run, selective removal of designated trees, coupled with brush disposal and appropriate use of prescribed fire, will not only improve forest  and tree health, but also greatly reduce the probability of bark beetle outbreaks and catastrophic wildfire.


See also: Bark Beetle Questions and Answers -->

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