Study: Keystone Western bumblebee is in trouble

Heat, drought and pesticide use is contributing to a wide-spread decline in the Western bumblebee, a once common and key pollinator across Montana and the West.

The Western bumblebee has seen a 57% decline over its range in the past few decades, the study, done by U.S. Geological Survey Scientists William Janousek, Marharet Douglas, Syd Cannings and Tabitha Graves.

Graves does her research work from her office in Glacier National Park. In Glacier, native pollinators are critical for pollinating flowers and plants of all sorts, most notably huckleberries and other berry species, which are a critical food source for a host of animals, like bears and songbirds.

The researchers looked at field data gathered over 22 years, including pesticide use and temperature data.

“Using 14,457 surveys across 2.8 million square kilometers (1.8 million square miles) in the western United States, we found strong negative relationships between increasing temperature and drought on occupancy and identified neonicotinoids as the pesticides of greatest negative influence across our study region,” the study found.

In addition to pesticides, which kill the bees, heat and drought were main concerns. 

“Recent range-wide declines in Western bumblebee were most strongly linked to climate conditions, particularly increasing temperature. Increased temperatures also correlate to contractions in the distribution and relative abundance of other bumble bee species globally. Changing climate conditions can affect bumblebee populations directly by influencing bee survival and foraging activity and indirectly by altering floral resource availability. Higher temperatures increase the likelihood of species reaching their thermal limits, reducing their ability to forage during hot days, and Western bumblebee ranks among the most sensitive bumblebee species to heat stress.

“Extended heat waves, which are expected to increase in the future, could be increasingly detrimental on bumblebee populations. We found temperature during the warmest quarter of the year to be the most informative in modeling Western bumblebee  occupancy; however, stress due to warming temperatures can occur year-round. Increasing temperatures can affect all bumblebee life stages and queens may be especially sensitive while overwintering underground,” the study noted.

In other words, warm winters are also bad for bees.

The models suggest things could get worse for the bees.

“Even considering the most optimistic scenario, westernbumble 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 Graves. “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.”

Graves noted that even in places like Glacier Park and eastern Montana, which includes the Northern Rockies Ecosystem, where pesticides generally aren’t used as much, if at all in some places, bees have declined.

Just not as much.

In the Rockies, bees declined 37% in occupancy, while the average was studywide was58%. Still, the reduction is significant. In 1990, the Rockies surveys found Western Bumblebees about 77% of the time. Now, it’s about 48%.

Heat stress is also a factor. The hypothesis is when it gets too warm, the bees can’t fly as far. Heat and drought also impact flowers and the quality of pollen.

Research continues on which plants the bumblebees prefer and whether weeds play a role. Graves is also doing research on huckleberries and the role of pollinators is part of that work.

There is significant concern.

“There has been an ongoing global decline in pollinators, including in North America,” said Janousek. “The decline in the once common western bumblebee shows that common, widespread species are not excluded from this trend and our study showed that climate change is an important reason for the decline of this native bee species.”

In 2015, the bumblebee was petitioned for listing under the Endangered Species Act.

“Losing even a single common pollinator species can disrupt the entire pollinator networks, with abrupt consequences for the species that directly or indirectly rely on them for food, including humans which benefit from crop pollination services of $1.5 billion annually in the United States alone,” the study notes.

Folks can do simple things to promote bumblebees and other bees in their yards. For one, plant plenty of flowers and secondly, leave some woody debris and like materials in the yard. Bees like to nest in downed woody material.