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Pine Beetles: the Why's and Wherefore's

  • Faster than a speeding bullet.
  • More powerful than a locomotive.
  • Able to leap tall buildings at a single bound.

Pine Beetle damage is rampant across the Western United States from British Columbia all the way across the Rocky Mountains down to the Southwest and Mexico.

Mountain Pine Beetles have existed and damaged trees for eons. Our current problem a is natural phenomena that has gotten out of hand.

Pine beetle damage in Rocky Mountain National Park, Colorado

Pine Beetles thrive in warm weather. Regardless of why the earth is experiencing climate chaos, the Mountain West has experienced warmer than usual winters for the past decade. Because Pine Beetles winter over through the cold weather, and they don't die unless the temperature reaches about 30° below zero for several days, there has been very little beetle mortality in the snow season. The population has not been winnowed down each year as was the case for centuries before.

The sustained broods hatch from the "host tree" and fly to their next victim tree just as soon as the weather reaches a balmy 60+ degrees. That usually means about June in the lower elevations, July in most mountain regions or July-August in the higher elevations. If you live in the Southwest (New Mexico or maybe Flagstaff, Arizona), they may even fly, lay eggs, hatch and fly again in just one season.

Both New Mexico and Montana engaged in a furious battle with THE BEETLE in 2014! Both states experienced a huge up-tick in infestation again last year that continues through this season. The New Mexico Forest Service is recommending treating twice this season: Once in Spring, and again in August to keep protection going through November and snow season. Ruidoso has been particularly hard hit. Montana added Missoula, Kalispell, and Billings to the list of hard-hit areas. And the beetles continue to move.

To make matters worse, replacing the Mountain Beetle in states that wanted to breathe easier like Colorado is the Douglas Fir & Spruce Beetle. Because the climate has been so mild over recent winters, the Fir & Spruce beetles are beginning to emerge as a new scourge.

Lodgepole Pine, White Pine, Ponderosa Pine, and Limber Pine are the most common victims of Mountain Pine Beetles, although several other species are at risk. Beetles home in on "terpines", which are pine odors that identify which trees they desire. They are also attracted to saps produced by damaged trees, and consider them desirable targets due to their weakened condition. (Healthy trees are sometimes able to defeat the beetle's attempts to drill in, so weak trees are often targeted.)

Given the choice, Mountain Pine Beetles choose the largest diameter trees. When those are gone, they will attack smaller trees. They continue to march (mostly the direction the wind blows) until they have gobbled themselves to the end of the trees. Colorado, which had several million acres under siege 5 years ago, is down to about 1 million active acres today due to the lack of living target trees in previously heavily infested areas. No trees, no beetles.

Female beetles attack a tree first and then release "trans verenol", a pheromone that attracts male beetles. As the males arrive, they release exo brevicomin which attracts female AND male beetles. The pheromone "cocktail" blows down wind, and brings in large numbers of beetles. This is what makes the Mountain Pine Beetle so wonderfully efficient: it's ability to mass attack one tree, defeat the trees defences and then move on to the next one (usually close by).

Fungus on pine trees

Fungus on a pine tree.

The Pine Beetle itself is not the culprit that actually kills the tree. As the female bores into the bark and down into the sub layer where she builds a nesting chamber and lays eggs, she carries with her a fungus (known as Blue Stain Fungus) that infects the trees. The fungi stops the tree from producing resin to pitch out or kill the beetle, thus enabling the beetles to attack and reproduce with impunity.

The fungi also blocks nutrient-conducting columns, inhibiting the flow of nutrients and eventually starving the tree

The fungi cannot be seen until a tree is already cut down.

Pitch tubes on pine trees

You can recognize a pine-beetle-attacked tree by its characteristic "popcorn" pitch tubes. They are wads of pitch that the tree has produced as a sort of sap trap to encase the boring beetle before it can penetrate to the phloem layer of the tree. If the sap is successful no harm is done to the tree and the beetle attack is thwarted.

Trees that are damaged and weakened by drought conditions such as the droughts concurrent with the warmer temperatures in the West, have little moisture to produce adequate pitch tubes for natural protection from the beetles.

Pitch Trap

To make matters worse, attacked trees that cannot produce adequate pitch may not be as obvious to the naked eye looking for pitch tubes. In that case, you should keep an eye on the ground at the base of any suspected trees for "frass", the sawdust produced by boring beetles that falls to the ground around the trunk.

Infested trees can also be recognized by their characteristic red (rusted) tops. They begin to rust in just a few weeks, so trees attacked in late summer will be "rusting" by Labor Day.

tree burner

What about dead trees?

Beetles will live through a season inside of a dead tree as easily as if it were alive.


Cutting the tree will not stop the beetle unless you also discard the tree properly. It must be cut up and taken to a local collection yard where they burn them. Or you must de-bark it so that the beetle larvae are exposed and dehydrate before metamorphosizing into adults. Chipping it with a big chip machine will also expose the beetle larvae, but fresh chips can attract Ips Beetles. Slash also attracts Ips Beetles, so unless you want to trade one scourge for another, be sure to clean up all limbs and twigs as well as the trunk.

In all cases, cut the tree before the seasonal "fly" of the beetle. You just can't save it. And it is the mother lode for the next infestation cycle. Trees with clean, round exit holes visible on the bark (look like little b-b holes) have already let loose their minions and are no longer infectious to the forest.

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