Using historical records to explore long-term trends in bumble bee ecology

Bumble bees are crucial pollinators of many natural and agricultural systems. Their recent declines, in the Midwestern United States and beyond, have been marked by notable shifts in phenological patterns, as well as spatial extent. Bumble bees have suffered from diverse stressors, such as climate change, habitat loss, pathogens and pesticides. Preserved specimens can be a valuable way of capturing long-term ecological changes; their associated data can be used to glean information on species’ distribution, nutrition, and even genetics. Bumble bees, in particular, are strong candidates for specimen-based research, as large, charismatic insects that are often over-represented in museum collections. I used preserved specimens from over 35 unique sources to study ecological changes in nine common Indiana bumble bee species from the early 1900s until present. Using quantile regression, I tracked shifts in phenology by estimating the rate of change for the onset, mid, and end dates of the bumble bee flight period throughout history. I found that for most species, the mid and end dates of activity have significantly advanced over time, while flight onset has delayed. While the onset delay was unexpected, this trend could suggest major reductions in flight activity for many important bumble bee species. Next, I created two occupancy models to estimate the effects of crop richness and temperature of county-level bumble bee occupancy. I found that for most species, the probability of occupancy increased over time, however most species responded negatively to increased temperatures. Crop richness did not have a significant effect on occupancy. With future climate warming, some bumble bee species are likely to perform better than others in Indiana, which could lead to significant restructuring in pollinator communities. Bumble bees have gone through major ecological change in the past century, with more changes certainly to come. With declines already in motion in the Midwest and beyond, it is crucial to continue monitoring our pollinators if we are to understand how to best conserve their populations.