Variation in Foraging Preferences by Bumble Bees Through Time with a Focus on Bombus affinis Conservation

Abstract

Bumblebees (Bombus spp.) provide valuable pollination services to both wild Plant communities and crops. Given the decline of some bumble bee species and the recent placement of the rusty patched bumble bee (Bombus affinis) on the endangered species list, efforts to conserve these insects are crucial. Understanding floral preferences of individual Bombus species can give insight into the importance of each Bombus species as pollinators of specific plants, whether there are plants serving as common resources, and the importance of individual plant species to Bombus species. However, little is known about the foraging behavior of bumble bee species, particularly Bombus affinis, as it relates to how plant preference varies throughout the day (diurnally) and between years (interannually). To fill this gap, we constructed plant-pollinator networks using data collected from photographic surveys conducted at the University of Wisconsin-Madison Arboretum. We found that there was no significant difference in foraging behavior diurnally between species, but that the foraging behavior significantly differed interannually between species, in some years. We also found that the number of plant species visited changes both diurnally and interannually. Finally, we found that Bombus affinis visited a range of plant species which differed interannually. These results suggest that external factors, such as climate change, may affect the bumble bee community interannually, from phenology changes and early onset of spring. Habitat fragmentation, in turn, may explain the lack of difference between diurnal foraging because bumble bees may have to rely on the plant species closest to them. Future studies should further explore the effects of climate change on phenology and the effect patchy floral resources may have on the foraging behavior of bumble bees, particularly B. affinis.