Metabolomic analysis of pollen nutrients collected by wild bumble bees in the Sierra Nevada Mountains

Kaleigh Fisher, Entomology, University of California at Riverside, Riverside, CA, Michelle Duennes, Saint Vincent College, Jay Kirkwood, University of California, Riverside and S. Hollis Woodard, Entomology, University of California Riverside, Riverside, CA

Background/Question/Methods
Bumble bees are generalist pollinators that collect nectar and pollen from a variety of floral resources. Although interactions between macronutrients (carbohydrates, proteins, and lipids) and bumble bee foraging preferences have recently begun to be explored, micronutrients, particularly those in pollen, have received far less attention. Here, we explored whether pollen nutrients present in worker-collected pollen varied between workers of two bumble bee species, Bombus vosnesenskii and B. melanopygus, collected from 17 different sites (different floral resources available) throughout the Sierra Nevada Mountains. Relative quantities of pollen nutrients across our samples were assessed using LC-MS for targeted and non-targeted polar and non-polar metabolites. We organized metabolites based on compound classes (i.e., amino acids, fatty acids, alkaloids, and sterols) that have been shown to be important in brood and colony development in honey bees and bumble bees.
Results/Conclusions
We collected pollen from 38 B. melanopygus workers and 45 B. vosnesenskii workers, and identified 79 polar metabolites and 210 non-polar metabolites in our final dataset. We found variation in nutrient levels between samples from different species, and between individuals from different habitats within a species, for the following amino acids: Betaine, Hydroxproline, Pipecolic Acid, Glutamine, Glutamic Acid and Arginine; fatty acids: Linoleic acid and Linolenic acid; and alkaloids: Trigonelline; and sterols: beta-sitosterol, campesterol, episterol, and stigmasterol. All of these nutrients are important for bumble bee brood and colony development. Recent evidence has suggested that bees may be able to directly detect amino acids, which may impact their foraging preferences. Similarly, sterols are exclusively obtained by bumble bees from floral resources as they cannot synthesize these compounds unlike other bee species. This is the first study that uses metabolomic analyses to quantify pollen nutrients collected by wild-caught bumble bees and provides a foundation for how variable pollen nutrients are across species collected from habitats with varying floral resources.