ARS | Publication request: Patterns of widespread decline in North American bumble bees

Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 24, 2010
Publication Date: January 15, 2011
Repository URL: http://www.pnas.org/content/early/2011/01/03/1014743108.full.pdf+html
Citation: Camerson, S.A., Lozier, J.D., Strange, J.P., Koch, J.B., Cordes, N., Solter, L.F., Griswold, T.L. 2011. Patterns of widespread decline in North American bumble bees. Proceedings of the National Academy of Sciences. 108: 662-627.

Interpretive Summary: About 50 species of bumble bees are native to North America. Of these, about 10% are thought to be declining either in the size of their geographic range, or in abundance throughout their respective ranges. Despite observations and mounting evidence of these patterns, little is known about the full range of declines or the causes underlying them. Here we present evidence of species range contraction for four species and concurrent declines in abundance of the same species. We contrast the declining species with four stable species, two in the Eastern U.S. and two in the Western U.S. Across the country we found that declining species had higher levels of one pathogen and lower levels of genetic diversity than the stable species, suggesting that pathogen may be important in the declines and genetic diversity could be another factor. Despite these results, no single causal factor emerged to explain the concurrent declines of these four species.

Technical Abstract: Declining abundance and range shifts of bumble bee (Bombus) species have been observed in Europe and Asia. However, the status of North America’s bumble bee species has been largely unstudied. Recent reports based on local or regional observations suggest that parallel declines are taking place in North America, yet a national assessment of species status is lacking. We provide evidence from a nationwide study that four bumble bee species are undergoing population decline and widespread range reduction in the U.S., while other species of bumble bees remain abundant throughout their ranges. Declining populations exhibit significantly reduced levels of genetic diversity and higher prevalence of the fungal pathogen Nosema bombi relative to abundant species of bumble bees. Knowledge of the causes of bumble bee population decline is of vital interest for ensuring future delivery of pollination services and provides a basis for experimental research on differential susceptibility among species of this important pollinator guild.