Mountain Pine Beetle

Laramie County Conservation District Mountain Pine Beetle

Popcorn like globs of sap or pitch oozing out of entrance holes made by Mountain Pine Beetle (MPB).  MPB came into Cheyenne inside infested firewood.

No Need to Spray

 The District is not recommending spraying for beetles.

Thanks in large part to the aggressive measures by homeowners, the District has not seen a new Mountain Pine Beetle tree in the Cheyenne area for over two years.  There is no need to spray for Mountain Pine Beetle this year.

While the Emerald Ash Borer has been identified in Boulder, Colorado, none have been seen in Wyoming.  Until they pose more of a threat in the area, the District does not recommend spraying or other insecticide applications for them.

The District has also not seen new infections of the Spruce ips Beetle recently, therefore, spraying of spruce is not necessary.

While the aggressive spraying has limited the damage to trees, spraying is detrimental to other insects.  The spray kills every insect in the tree and the drift kills adjacent beneficial insects.  Spraying should be only as necessary to limit damage to beneficial insects.

Detailed Information on Mountain Pine Beetle  

Mountain Pine Beetle (MPB) attacks any pine tree including Scotch or Scots pine, Lodgepole pine, Ponderosa pine, Limber pine and Austrian pine. Initially, trees are attacked by MPB when they are under stress from drought, root or trunk damage, soil compaction, or herbicide damage. Healthier trees will be attacked as the insect population increases in the area. Beetles first came into Cheyenne inside firewood from trees that had been infested with MPB, usually from mountain forest sources.

Adult beetles emerge from attacked trees in mid-June through mid-September. Mid-August on average is the peak emergence time for beetles in Ponderosa pine. The adults fly to green pine trees and chew a hole into the bark. Sometimes the sap oozing out of the tree “pitches-out” the beetle.

Trees under drought stress or in poor health may not ooze sap. If the attack is successful, a beetle pair mates and the female chews a vertical tunnel where up to 75 eggs are laid. The eggs hatch and the larvae feed horizontally away from the vertical egg gallery. The feeding of hundreds if not thousands of larvae will girdle the tree, cutting off the flow of food and water throughout the tree trunk. MPB adults typically carry spores of blue stain fungus on their bodies. The blue stain fungus helps weaken the tree by growing in tree cells that function in food and water transport. The growth of the fungus aids a successful beetle attack by possibly slowing or stopping the sap flow in the tree.

Heavily attacked pines will not die immediately. A dying tree can stay green for up to 8 to 12 months after a heavy MPB attack. MPB spends the winter protected under the bark in larvae stage and sometimes into the adult stage. In the spring, the larvae begin to feed again. A few adult beetles survive the winter, allowing them to continue to lay eggs in the spring or emerge from the trees and attack other trees. The larvae enter pupae stage in June and July. Adult beetles emerge from the pupae stage and chew their way out of the tree and fly to green pines. Several adult beetles may use the same exit hole. The MPB have one generation per year.

Storing or Transporting Firewood

Ideally, pine tree trunks destined to be firewood should have stood in place for at least one year after the needles have fallen off of the tree (two years after bark beetle attack,) or be well seasoned or dry. Otherwise, it should be assumed that any pine tree wood has a possible life stage of MPB inside under the bark.

Firewood should be securely covered with one or two layers of 6 mil thick clear plastic tarp treated with UV inhibitors to make the plastic resistant to sun damage. MPB can sometimes chew through the plastic, but at least the number of beetles attacking green pines will be reduced.

  • Pine trunks with the bark peeled off can be stored as firewood without being covered.
  • Transporting uncovered firewood during the adult beetle flight period (mid-June through mid-September) could spread the beetle from the mountain forest to your yard.
  • The best precaution is not to transport any wood that could contain Mountain Pine Beetle.
  • Take all necessary precautions from spraying your pine tree trunks to carefully selecting and storing your firewood, or next year’s firewood may come from your own yard.

Please click here for an informational brochure on the Mountain Pine Beetle.