- Apply to UW
- Programs & Majors
- Cost & Financial Aid
- Current Students
- UW Life
- About UW
Published February 10, 2023
The western bumblebee was once common in western North America, but increasing temperatures, drought and pesticide use have contributed to a 57 percent decline in the occurrence of this species in its historical range, according to a new U.S. Geological Survey (USGS)-led study involving a University of Wyoming scientist.
Using data from 1998-2020, scientists determined that increasing summer temperatures and drought partly drove declines of the native western bumblebee in recent decades, with rising temperatures particularly important. The research group included Lusha Tronstad, lead invertebrate zoologist with UW’s Wyoming Natural Diversity Database (WYNDD). The study was published recently in the journal Proceedings of the National Academy of Sciences.
The decline in pollinators is a cause for concern because most flowering plants depend on pollinators such as the western bumblebee to promote reproduction. Pollinators also are essential to the agriculture industry and economy, providing fruits, seeds and nuts that both humans and wildlife rely on.
“Wyoming is predicted to have some of the last remaining suitable habitat for western bumblebees under future climate change scenarios,” says Tronstad, who has published previous research on the topic as a member of the Western Bumble Bee Working Group. “WYNDD has been working closely with state and federal agencies to learn more about bees, including the western bumblebee, in our state, which contributed data to the range-wide analysis in the study.”
To further complicate matters for the western bumblebee, climate change continues to make rising temperatures and drought more common in the Western states.
“There has been an ongoing global decline in pollinators, including in North America,” says Will Janousek, USGS scientist and co-lead author of the study. “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.”
The research team found another reason for the reduced distribution of the western bumblebee in a pesticide use dataset spanning 2008-2014: a group of insecticides called neonicotinoids, which are commonly used in agriculture. In areas where neonicotinoids were applied, the western bumblebee was less likely to occur and, as the rate of neonicotinoid application increased, the bumblebee’s presence declined further.
The scientists also projected the future status of the western bumblebee in 16 regions of the western United States in the 2050s under different future scenarios, considering increasing levels of future climate stressors, changing forest and shrub cover, and other factors.
“Even considering the most optimistic scenario, western bumblebee populations are expected to continue to decline in the near future in nearly half of the regions across the bumblebee’s range,” says Tabitha Graves, USGS scientist and co-lead author of the study. “Considering the more severe, but probably more likely scenarios, western bumblebee populations are expected to decline an additional 51 percent to 97 percent from 2020 levels, depending on the region.”
This study was a collaborative effort among the USGS, U.S. Fish and Wildlife Service, U.S. Department of Agriculture-Agriculture Research Service, UW, Dickinson College, Canadian Wildlife Service, Montana State University, Xerces Society for Invertebrate Conservation, the University of Colorado-Boulder and Ohio State University.
For more information on bumblebee research in the West, visit the USGS Northern Rocky Mountain Science Center website.