What are the bees' needs? Analyzing the diet breadth for three Rocky Mountain Bumble Bees

Abstract

Bumble bees are crucial pollinators in both natural and agricultural ecosystems. For effective conservation of this important group of pollinators, it is essential to understand their basic ecology, such as their interactions with floral food resources. In this study, we used a long-term dataset (5 year) of season-long bumble bee floral resource use to investigate the floral diets of three common bumble bee species native to the Colorado Rocky Mountains (Bombus bifarius, B. flavifrons, a nd B. appositus). We compared the floral diet richness among the three species overall and also among the castes (queens, workers, males) within each species. Our analyses revealed that floral diet richness differs among the three focal bumble bee species, which we hypothesize is due to variation in species phenology and morphology. When comparing the floral diet richness within species and across the different bumble bee life stages (i.e. castes), we found a clear distinction between workers and reproductives (males and queens) in species that emerge earlier in the season, while the later emerging B. appositus had consistently low diet richness in all castes.We gained a better understanding of their individual diet breadths, and how different castes take advantage of floral resources throughout the summer. This study provides important information on the basic ecology and resource needs of an important group of pollinators, and suggests that focusing one what life stage of bumble bees overlooks important variation. Key words: Bombus, B. appositus, B. bifarius, B. flavifrons, corolla length, diet breadth, phenology, physiology, plant-pollinator interactions, pollination