by Carolyn Bernhardt
December 10, 2026
For decades, the Great Plains has served as a buffer, protecting Minnesota from an established population of the mountain pine beetle (MPB, Dendroctonus ponderosae) in South Dakota. The species is native to western North America but is slowly spreading east. When populations reach epidemic levels under the right conditions, they can devastate forests; they tunnel under the bark and spread fungi that kill trees. Researchers have learned a great deal over decades about how mountain pine beetles affect South Dakota forest stands during outbreaks, but little is yet known about how they persist in the Black Hills region when their numbers are few and far between, or what helps their populations soar in a given area.
With a round of MITPPC funding that began in early 2024, the Aukema Lab is focused on better understanding the inherent risks that may facilitate MPB’s establishment here in Minnesota, as well as the buffers that may help constrain it. Mapping the constellation of ecological conditions and events that must align for an MPB outbreak to occur can help land managers improve early-detection surveillance strategies. They can use this information to strategically allocate their time and resources to Minnesota forests most at risk of invasion by the mountain pine beetle.
Population fits and spurts
“In the past 20 years, the mountain pine beetle has expanded its range into forests where the beetle has never been before,” says Ella Maddi, a graduate student in the Aukema Lab. This includes a massive stretch of jack pine that extends across Canada into the Great Lakes region. And climate change, she says, dramatically increases the risk of beetles arriving in Minnesota. “The beetle would have a major impact on our northern pine forests.”
As the team embarked on their studies, Shealyn Malone, PhD, a postdoctoral associate in the Aukema Lab, says she was surprised to find such a high extent of MPB-impacted forest in the Black Hills. “Since 1997, nearly all regions have been impacted to some degree.” Blossoming MPB populations at the Wyoming-South Dakota border might feel distant to Minnesotans, but according to Malone, “It’s a numbers game.” The more beetles there are nearby, the more likely they are to show up in Minnesota.
“Mountain pine beetle is an eruptive species,” says Maddi. Meaning that, although they are incredibly destructive when their numbers surge, population levels can plummet in between outbreaks—sometimes for up to 60 years. So, where do MPBs go when they are not reaching epidemic status?
The scientists turned to lightning-stricken trees as a potential MPB safe haven. The team identified and cut down trees struck by lightning to search for beetles lurking within, but they didn’t find any. Maddi says the greatest challenge with studying the endemic mountain pine beetle is how cryptic they are on the landscape. The MPB not only nestles under bark, but it also has a short dispersal window. “This really impacted our lightning-struck tree experiment,” says Maddi.
“Not only is MPB elusive at endemic levels, so are lightning-struck trees,” adds Malone. “We know very little about the impact of lightning on individual trees and forest communities, so Maddi’s work will offer novel insights into how these two elusive phenomena may interact.”
Fungi-carrying travelers
Many characteristics make the mountain pine beetle difficult to outstep. Maddi cites their symbiotic relationship with fungi, which at once supplies them with nutrients and protects them from tree defenses. A tiny indent in their cheek allows them to pocket fungal spores as they dart between host trees.
And while MPB can usually only hop from host to host, up to about 100 feet at a time, they can gradually meander nearly 15 miles. “MPB have been found tens to hundreds of miles from potential [host trees], such as in snowfields above the timberline,” says Malone. So, they can likely travel on the wind.
Thankfully, the light smattering of trees across the Great Plains present the mountain pine beetle with a rather inhospitable landscape. Still, Malone says, several “pine islands” between Minnesota and the Black Hills could help MPB traverse the desolation. Plus, people moving about the area, including those carrying infested firewood, could inadvertently help facilitate MPB’s eastward movement.
But every insect, no matter how mighty, has potential adversaries near their habitat. The Aukema Lab wants to better understand which species MPB would have to compete with in Minnesota. Understanding MPB’s competition before the beetle arrives could help experts better predict where the MPB would be most likely to thrive.
Maddi says, “For this experiment, we set up traps for bark and wood-boring beetles.” The team then compared how many subcortical beetles (those living under bark) they trapped in Minnesota and in South Dakota, as well as the species diversity in the two states. The researchers are still analyzing their data, but some preliminary findings have emerged. “First, we found five species of pine sawyers, a type of wood-boring beetle, in Minnesota,” says Maddi, “and only one in the Black Hills.” However, the overall number of beetles was about the same in both states.
What makes the population boom?
Meanwhile, Malone set to work determining the factors driving the beetles to epidemic levels. While populations may wane in certain areas between outbreaks, the beetles’ ability to survive by lying in wait helps it eventually reach new feasting territory. And the surging populations are the culprits behind widespread tree mortality.
By combining decades of USDA Forest Service aerial survey data and climate datasets with spatial statistical models, the lab is analyzing past outbreaks in the Black Hills to identify key drivers behind MPB outbreaks, such as weather and the density of host trees. Their findings should help pinpoint the conditions that relate most to MPB outbreaks in this region, as well as when surrounding regions like Minnesota may be most vulnerable to invasion.
“I think it’s also worth noting that the MPB population in the Black Hills is genetically distinct from populations in Canada and the southern Rockies,” Malone says. Western populations have been the focus of most research to date. Understanding outbreak drivers in “nearest-neighbor” populations may help scientists gain insight into the population closest to Minnesota.
Malone says their research helps answer key questions about their potential arrival. “If MPB individuals make it into the Great Lakes region, will this translate to population establishment?” she asks. “Will they have the capacity to outbreak similarly as they do in western forests? Will they be able to maintain endemic populations during non-outbreak times? Our research helps to answer these questions so we are more prepared with knowledge of how this insect may interact with our forests.”
The Minnesota Invasive Terrestrial Plants and Pests Center research is supported by the Environment and Natural Resources Trust Fund, as recommended by the Legislative-Citizen Commission on Minnesota Resources.
Stay connected by signing up for the MITPPC newsletter.
More information
- Quantifying the endemic niche of mountain pine beetle, research project
- Mountain pine beetle information, Minnesota Department of Agriculture
- Mountain pine beetle identification and biology, South Dakota Department of Agriculture and Natural Resources