Laura Lundquist

(Missoula Current) Temperatures are still cool in western Montana, but with days getting longer, the first plants of spring will soon make an appearance. Unfortunately, a once-common pollinator might not be around to visit the wildflowers.

Researchers associated with the U.S. Geological Survey and the University of Montana have determined that the western bumble bee, once common throughout the West, is now increasingly rare or absent in some regions due to rising temperatures, drought and pesticide use. The study was published in the Proceedings of the National Academy of Sciences in late January.

The first year of bee data for the study came from 1998. By then, western bumble bees were already in trouble because commercial breeding of the bees for use in greenhouse pollination had allowed a fungal pathogen to spread into the wild population. The first indication of population declines were noticed in 1998, so commercial breeding was abandoned in the early 2000s.

In 1998, western bumble bees were most likely to be found in more mountainous areas but were also prevalent in the plains of eastern Montana and Wyoming and the desert regions of Nevada, Utah and Arizona.

In 2015, groups petitioned the U.S. Fish and Wildlife Service to list the western bumble bee as threatened, after research found the fungus wasn’t the only problem. Localized studies found threats from other diseases, habitat destruction, lethal and sublethal effects of pesticides, climate change and competition with nonnative honey bees.

By 2020, surveys and modeling showed the bees remained abundant only in the high Rocky Mountains and the Sierra and Cascade ranges and appear to be almost absent in the lowlands of Arizona, Utah and California. Bee occupancy across the West had declined almost 60% on average, but areas such as southern Arizona experienced declines as high as 83%.

To find how various threats worked against bees across the entire West, the researchers used a computer model to overlay about 20 years of data related to climate change and land use and other data related pesticide use between 2008 and 2014.

The model showed that increasing summer temperatures and drought partly drove the declines, with rising temperatures having the most effect. It also showed that, in areas where neonicotinoid pesticides were applied, the western bumble bee was less likely to occur, and, as the rate of neonicotinoid application increased, the bumble bee’s presence declined further.

Neonicotinoids kill insect pests by attacking their nervous system, but it does the same thing to bees, aquatic insects and even birds. Neonicotinoids were introduced in the mid-1990s, and their use has surged to where they’re now 25% of the global pesticide market.

The researchers then used their model to predict how bees would do 30 years into the future under different scenarios, considering increasing levels of climate stressors, changing forest and shrub cover, and other factors.

The answer: terribly.

“Even considering the most optimistic scenario, western bumble bee populations are expected to continue to decline in the near future in nearly half of the regions across the bumble bee’s range,” said co-author Tabitha Graves, USGS scientist out of West Glacier. “Considering the more severe, but probably more likely scenarios, western bumble bee populations are expected to decline an additional 51% to 97% from 2020 levels, depending on the region.”

Bees in a bee box. (Martin Kidston/Missoula Current file)
Bees in a bee box. (Martin Kidston/Missoula Current file)

The authors said losing even a single common pollinator species can disrupt entire pollinator networks, with abrupt consequences for species that directly or indirectly rely on them for food. That includes humans, which benefit from crop pollination services worth $1.5 billion annually in the United States alone.

The researchers are now studying what the loss of the western bumble bee could mean to various ecosystems.

Fortunately, after the scientists highlighted the decline in western bumble bees in a separate paper published a year ago, multiple states have started statewide surveys to increase their understanding of where the bumble bees are, Graves said.

The USGS scientists are also collecting more data in Glacier National Park and on Bureau of Land Management property in eastern Montana and the Dakotas.

“We’re trying to learn which bumble bees use which floral resources and what habitat is associated with the bees. There’s more we don’t know than what we know. But they are here in western Montana, especially in Glacier or the Flathead National Forest. They’ve been detected visiting species like huckleberries, snowberry and penstemon. They’re a generalist species, so it’s hard to know what the impact will be,” Graves said.

Contact reporter Laura Lundquist at