The mysterious population decline of the imperiled Franklin’s bumble bee, which once flourished in a small area of northern California and southern Oregon, is not due to pathogens, but most likely to population bottlenecks and environmental issues, such as fire and drought stressors, according to newly published museum genomic research in the Proceedings of the National Academy of Sciences (PNAS).
A nine-member team, led by conservation geneticist Rena Schweizer of the USDA Agricultural Research Services Pollinating Insects Research Unit, Logan, Utah, collected whole-genome sequence data from museum specimens of Bombus franklini, spanning more than four decades, to reconstruct 300,000 years of the bee’s genetic history.
Most of the specimens are from the Bohart Museum of Entomology at the University of California, Davis. UC Davis Distinguished Emeritus Professor and bumble bee conservationist Professor Robbin Thorp of the UC Davis Department of Entomology and Nematology monitored the B. franklini population for 21 years, from 1998 until his death in 2019, and collected specimens. He was instrumental in obtaining species protection under the U.S. Endangered Species Act.
“Understanding what was happening to Franklin’s bumble bee was Robbin Thorp’s last major project before his death,” said UC Davis Distinguished Professor Emerita Lynn Kimsey, who directed the Bohart Museum for 34 years until her retirement in 2024. She is a co-author of the paper.
The bumble bee has not been sighted in the wild since 2006 and is feared extinct. Its range, a 13,300-square-mile area confined to Siskiyou and Trinity counties in California, and Jackson, Douglas and Josephine counties in Oregon, is thought to be the most limited geographic distribution of any bumble bee in North America and possibly the world.
PNAS published the paper, “Museum Genomics Suggests Long-Term Population Decline in a Putatively Extinct Bumble Bee,” in its Oct. 20 issue.
