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Mountain Pine Beetle


Mountain Pine Beetle in the Black Hills

Beetle Biology:

The mountain pine beetle (Dendroctonus Ponderosae) is one of several common bark beetles native to North America. Originally discovered in the Black Hills in the late 1800’s, this tiny tree MBPsizekiller was first named the “Black Hills Beetle”, which was later changed to “mountain pine beetle” after it was documented throughout the Rocky Mountain West. Pine beetles evolved with western forests of the US and primarily attack ponderosa, lodgepole, scotch, and limber pines.
IMG_0272Beetles like these are omnipresent in nearly all forested systems. Most times, they exist in what are called endemic populations, killing only a few already weakened and stressed trees per year. But when conditions become prime, beetle populations skyrocket to epidemic proportions,  otherwise known as an outbreak. The outbreak would typically begin in an especially dense area of forest, spreading outward until it reached a forest type that was inhospitable for the beetles. While there are a number of factors that contribute to the intensity and scope, the main driving force behind an outbreak is over-stocked mature forests.

In other words, there are too many trees that are all relatively the same age class. Most mountain pine beetle epidemics have originated in even-aged, high density stands.  Although numerous factors contribute to epidemic mountain pine beetle populations, over-stocked ponderosa pine stands are the major contributor to mountain pine beetle epidemics
-John Schmidt
Retired Entomologist
United States Forest Service/RMRS

On the Black Hills National Forest today, however, years of fire suppression and insufficient management have produced a forest that is literally “infested” with trees. This phenomenon equates to large expanses of “prime beetle habitat” (overly dense stands comprised of 8” and larger trees) and therefore little exists in the way of natural barriers to the beetles' progression. It has often been quoted by researchers and biologists studying this mountain pine beetle, that “the Black Hills don’t have pine beetle problem, they have a tree problem”.

The mountain pine beetle completes its life cycle in one year.  In late July to early August, the beetle emerges from last year’s host tree (now dead) and seeks out the next available suited host tree.  This annual phenomenon is typically referred to as the “flight”.  Mountain pine beetle flights are unique in that they are synchronized, meaning that while some beetles may fly early, and some may fly later, the critical mass of beetles seem to emerge and fly simultaneously within a matter of days.  When a pine beetle lands on a suitable host tree, they emit a pheromone that attracts other beetles to mass-attack.  This is how these tiny beetles are able to overcome a tree’s defenses.

Boring through the bark, the pine beetle kills its host by disrupting the movement of food from the needles to the roots through the construction of tunnels known as galleries underneath the bark of the tree.  Here the pine beetles lay their eggs in late summer/early fall. Each beetle also carries a fungus disease known as blue stain from tree to tree; blue stain fungi plug the water-conducting tissue of the tree, blocking the flow of water from the roots to the needles. This combined attack is generally sufficient to kill an infected tree within one year. Soon the eggs hatch into the larvae stage, which soon become dormant in preparation for winter. The following spring, these larvae continue to mature and complete their metamorphosis into the adult stage. (pitch tubes)

Once a tree is attacked, it is too late to do anything to save it. The beetles generally attack trees in such large numbers – by the hundreds of thousands – that there is no doubt they can overcome the tree's only defense, heavy resin flow.
The best prevention against mountain pine beetles is maintaining unsusceptible stands.  This means having a healthy, thinned forest that is unattractive to pine beetles and does not allow them the opportunity to infest. 
For high-value areas, it is advisable to spray trees if there is noticeable activity in the area.  Spraying involves applying chemical to the bark on the bottom 30-40’ of the tree, ahead of the mountain pine beetle flight in late summer.  Ideally, the best time to spray trees are in the spring time.  Check which local chemical companies for pricing and availability.
It is also recommended to monitor forested areas that are at risk for infestations.  Sanitation, or the removal green-infested trees, is a very important method to stave off major infestation.  If possible, remove green-infested trees from the site.  A commercial timber harvest can facilitate removal of these green infested trees, but when unfeasible, ‘cutting & chunking’ the infested tree into 2’ sections is effective in killing the beetles.


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