Mountain Pine Beetle

Region 2 Beetle Information

FAQ - Mountain Pine Beetle

2016 Forest Health Report

(Below: May 2014 Article by Dave Thom. Thom is a Certified Forester, and is the coordinator for 14 private and governmental entities represented in the Black Hills Regional Mountain Pine Beetle Working Group.)

What’s Killing the Trees?

Visitors to and residents of the Black Hills cannot help but notice thousands of dead trees as they travel the scenic roads and visit area attractions. They are witnessing the mountain pine beetle. This naturally occurring, voracious, rice-kernel sized insect is killing ponderosa and other pines throughout the west and the Black Hills of South Dakota and Wyoming. The mountain pine beetle threatens public safety, watersheds, forest resources, high value and sensitive sites, recreation, aesthetics, some wildlife habitats, and to increase potential for larger, more intense wildfires.

The reddish brown trees evident in summer were actually attacked the previous summer/fall when adult beetles emerged from infested trees and sluggishly flew to adjacent trees to bore into the bark leaving whitish/rust pitch masses. The adults burrow vertically beneath the bark laying eggs and spreading fungus spores. The eggs hatch and begin to metamorphose into tiny white larvae (“grubs”) that excavate their way laterally around the tree cutting off the flow of nutrients. The fungus, and its tell-tale blue stain, simultaneously clogs pores, further reducing life-giving flow of tree sap. The tree succumbs the next spring as the needles yellow and then turn brown in the summer.

Since 2010 forest analysts mapped 95,000 acres of new infestation using aerial photographs, not including additional infested areas that were cut or removed before they turned brown and were visible on high resolution photos taken from an airplane. In total, the beetle has encompassed about 430,000 acres since the epidemic started in 1996, about a quarter of the 1.5 million forested acres in the Black Hills. Fortunately, there is recent evidence the rate of spread is beginning to decline.

What is being done about it?

Beetles thrive in overly crowded ponderosa pine trees that are 6-8 inches in diameter and larger. Trees need food, water and sunlight to grow and remain healthy (much like humans!). Too many trees in a small area stress them and make them unable to resist insect attack. Healthy pines can often “pitch out” insects, but in an epidemic the mass attacking insect overwhelms tree defenses. The beetles freely cross from one land ownership to another. So, resolving this problem takes careful coordination among all the landowners and managing agencies to use the most effective treatments. Fourteen entities in the Black Hills Regional Mountain Pine Beetle Working Group are using a “collaborative, all-lands approach”.

Much of the mountain pine beetle work in the Black Hills is to thin trees to reduce competition and prevent major insect outbreaks. Thinning is done using commercial timber sale contracts. Smaller, poorer formed trees and those with insects are removed leaving more growing space for the larger trees. The more open-grown forest is favorable for grass and shrub growth and improved habitat for many wildlife species. About 25,000 acres is harvested annually that incidentally creates about 1,200 jobs. The open-grown forests of past tree harvest is readily visible along many area highways and promises a much healthier forest for the long-run.

In small, inaccessible areas, a timber faller “cut and chunked” beetle infested trees into small pieces less than 24 inches so they dry out, thus killing the developing beetle larvae. In 2013 “cut and chunking” contractors covered about 165,000 acres across the Black Hills protecting private land, high value places on public lands, and along county roads. Some landowners are spraying their highest valued trees with a registered insecticide that is very effective in preventing insect attack when done properly. These treatments have been very effective in reducing the rate of spread. Also, the beetle contributes to its own demise as it devours its food source, and predatory insects and fungi are slowly beginning to attack and reduce beetle populations.

The forests of the Black Hills are changing…or they are not. William H. Illingworth, while on General Custer’s Black Hills expedition in 1874 photographed a more open-growing forest caused by fire and insects. Photographer Paul Horsted, in 2002, photographed those same locations that showed much denser forests that developed over the last 135 years. Modern forest management, including careful use of fire, can recreate some of those conditions and ecological processes and restore healthier, more resilient forests for the long-term. It takes a collaborative, all-lands approach to do it. While much work remains to be done, we are making a difference!
Additional information is available from: Wyoming State Forestry (307-746-4261), South Dakota Resource Conservation & Forestry Division ( , or the Black Hills National Forest (




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