Bumble bees and agricultural landscapes of yesteryear: How a century of agricultural change has impacted bumble bee occurrence and community composition in the US Midwest

Agricultural intensification is a key suspect among putative drivers of recent insect declines, but an explicit link between historical change in agricultural land cover and insect occurrence is lacking. Determining whether agriculture impacts beneficial insects (e.g., pollinators), is crucial to enhancing agricultural sustainability. Here, we combine large spatiotemporal sets of historical bumble bee and agricultural records to show that increasing cropland extent and decreasing crop richness were associated with declines in 60% of bumble bee species in the agriculturally intensive Midwest, USA. Critically, we found that high crop diversity was associated with higher occurrence of many species pre-1950 - even in agriculturally dominated areas, but that current agricultural landscapes are devoid of high crop diversity. Our findings suggest that insect conservation and agricultural production may be compatible, with increasing on-farm and landscape-level crop diversity predicted to have positive effects on bumble bees.