Assessing declines of North American bumble bees (Bombus spp.) using museum specimens

Abstract

Bumble bees are an important group of wild pollinators in North America and considerable concern has been expressed over declines in their populations. However, before causes for declines can be assessed, it is essential that the geographical and chronological patterns of decline be discovered. Hitherto a lack of assessment of historical data has hindered our efforts to determine which species are most at risk. Here, the status of 21 North American bumble bee species (Hymenoptera: Apidae) occurring in the eastern nearctic biogeographic region is assessed using a specimen-level database from compiled museum and survey records dating back to the late nineteenth century from various institutional collections. Using a combination of measures, bumble bee declines were assessed over their entire native ranges. We report here that half of the selected fauna is in varying levels of decline (especially Bombus ashtoni, B. fervidus, and B. variabilis), with the remaining species exhibiting stable or increasing trends (e.g., B. bimaculatus, B. impatiens, and B. rufocinctus). Suggestions for prioritizing conservation efforts for this important group of pollinators are given.