Mountain Pine Beetle 101
The mountain pine beetle outbreak has reached epidemic proportions in Summit County.
In virtually every large stand of lodgepole pine, the red crowns of dead trees show the devastating effect of when pine beetles attack.
The impacts will not only be felt economically in property values but also by wildlife and watershed values.
You might ask, “How did this get started, and where did the beetles come from?” The answer is pine beetles evolved along with lodgepole pine – a relationship developed and refined during the last 215 million years. The relationship has to do primarily with the regeneration of new pine forests. Pine beetles are usually present in endemic numbers in the forest. But when conditions are right, the beetle population explodes.
In the high country present conditions are extremely favorable for the beetle. This perfect scenario for population explosion happened because of the large, unmanaged, over-crowded stands of old and stressed trees which were further weakened by drought, road building, and soil compaction and, along roadsides the application of millions of gallons of magnesium chloride.
As the beetle population increases whole stands may be killed and the dead trees create conditions for large, potentially catastrophic fires. Because many lodgepole pines have closed cones, it takes fire to open them. A fire not only opens the cones and allows seeds to disperse but also removes competing vegetation and creates a suitable seedbed for regenerating a new stand of pines.
Problems with this scenario arise when we remove the largest, genetically superior trees and their seeds which have become infested with beetles. Policies which restrict fires from developing diminish the process further. The result of no suitable seedbed and inferior seeds is the lodgepole being removed from the ecosystem.
Evidence of beetle infestation is popcorn-shaped pitch masses on the trunks. The pitch will usually have a hole in the middle where the beetle has penetrated. They can be differentiated from normal pitch by the presence of sawdust in them which gives them a pinkish cast.
Sometimes, the beetle will be pitched out. Normal pitch will be clear and shiny.
Sawdust rings around the base or in bark crevasses is another way to tell.
Woodpecker activity and corresponding bark flakes on the ground is another, but the best way to tell is the presence of the beetle itself. They can be found immediately under the bark. It takes a hatchet or screwdriver to pry the bark back.
Sometimes the beetle will not be successful and instead of finding tunnels and beetles you will find a white layer. This is the cambium and is present in all pines.
Another way of telling if the tree has successfully warded off attack is in the spring when the tree puts forth new growth, which is called candling. If a tree candles it will probably live at least through the current year.
Mountain pine beetles have a one-year life cycle. In late summer adult beetles leave the trees and females seek out new trees in which to raise a new crop. They usually look for the largest trees they can find because these trees have the thickest phloem.
The phloem is part of the cambium which is nutrient rich and feeds the developing larvae. The female beetle attempts to excavate a mating chamber and if successful secretes a scent (pheromone) to attract a male. Males and other females pick up this scent and attack the tree in mass. Once mated, the female bores a straight line tunnel and lays approximately 75 eggs. Enough beetles will emerge the following spring to infest between five to seven new trees.
The eggs hatch into larvae and this is the stage in which they spend the winter.
These larvae produce an anti-freeze like compound which protects them from extreme cold temperatures up to 40 below zero. In the spring larvae feed extensively, pupate and then adult beetles emerge in late July, peaking in mid-August. Some adult beetles may still be found flying in October.
Another element in the cycle is the presence of blue stain fungi. The adults pick up spores as they leave the original host tree and transmit it to the new tree. The fungus is important in weakening the tree by plugging the tree’s water transportation system. The associated rapid drying is why the trees turn brownish red so quickly in the spring.
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