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Haimowitz: Mountain pine bark beetle can be beneficial to forest management

by Wyoming Livestock Roundup

Laramie – The pine bark beetle, long thought to be a pest to the pines of northern forests, can increase diversity within forest ecosystems. 

Lawrence Haimowitz has been studying best practices to study the mountain pine bark beetle and determine their natural predators.  

About the beetle

According to the United States Forest Service (USFS), there are 600 different species of bark beetles in the U.S, with a range from Mexico to the Rocky Mountains. Most of these bark beetles only attack aging or compromised trees, but some species, such as the mountain pine bark beetle, will attack living trees in times of epidemic.

USFS labels the mountain pine bark beetle as the most aggressive, persistent and destructive bark beetle in the western U.S. and Canada. The beetle is estimated to have caused damage to over 1.5 million acres of forest in northern Colorado and southern Wyoming alone. 

The beetles lay their eggs within the bark of various pine trees, which begins the process of killing the tree. Once the beetles hatch, they begin consuming the bark of the tree. Through tunneling and a fungus carried by the beetle, the tree eventually dies. 

Trees, however, are not defenseless, explains Haimowitz.

He continues, pines use pitch to resist the beetle attacks and are largely successful against the beetle. 

“It typically takes thousands of beetles all at once for the tree to be compromised,” he says.

Learning more

Little is known about the natural predators of the beetle due to the difficulty associated with studying them. 

“It’s very hard to study this beetle because it spends most of its life underneath the bark of the tree where it can’t be observed,” says Haimowitz. “Previous methods were extremely labor intensive, costly and not very effective.”

Haimowitz tested two methods of studying the beetles in the Shoshone and Medicine Bow National Forests of Wyoming. His team found that the beetles could very easily chew through the shade and weed cloths used in previous studies. 

Haimowitz and team, however, did discover that the beetles could not chew through a metal mesh. 

Using a selective exclusion method, they were able to measure the effect of associated insects on bark beetle survival. 

Through this study, the team was able to identify two predators not previously associated with the beetle. 

Beetle epidemics

“From 2000-15, there was a very large beetle epidemic,” notes Haimowitz. “The timeliness of this issue really got me interested in studying the bark beetles.”

“Bark beetles burrow down only in mature pine trees to lay their eggs,” says Haimowitz. 

“Previous forest management practices and an overall warmer climate got us to where we are with beetle epidemic,” he comments, noting that an abundant food source for beetles allows the population of the insect to grow quickly. 

“For example, it used to be widely accepted that all forest fires were bad,” says Haimowitz. “Now, we know that fires can help return forests to natural levels of age diversity.”

“Since we tried to control all fires, there are now more mature pines than there should be, and the forests are extremely dense,” he says, noting that as the notion all fires are bad became commonplace, age diversity in trees dramatically decreased. “It is important to realize that fires can return forests to their natural levels of age diversity, which is extremely important in keeping beetle populations in check.”

According to USDA data, pine beetles have affected nearly 1.5 million acres of forest in Colorado and southern Wyoming. The epidemic is thought to have been triggered by an extreme drought in the early 1990s. 

“Beetle epidemics are natural,” Haimowitz states. “The beetles have evolved with the forest and the forest with the beetles.” 

Benefits of beetles

Despite the problems presented by uncontrolled beetle populations, at theend of the day, pine beetles can be very beneficial to forest ecosystems, says Haimowitz. 

Haimowitz explains that pine forests have evolved with natural fires and bark beetles, he describes the relationship as a three-partner dance. 

“If we take away one of the partners, as we did with non-selective fires, the dance can turn into chaos as we saw with the beetle epidemics,” says Haimowitz. 

Haimowitz comments that as fire is a widely used tool in forestry today, we may view beetles as a tool in the future. 

“In the future, beetle epidemics can be more self-limiting and contribute to a greater diversity of habitat,” says Haimowitz. “As foresters adopt better knowledge-based management practices, bark beetles will likely become another implement in the tool kit.”

Callie Hanson is the assistant editor of the Wyoming Livestock Roundup. Send comments on this article to

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