Floral Composition of Pollen Collected from a Rusty Patched Bumble Bee (Bombus affinis, Cresson) Nest in Southeastern Minnesota

 Understanding the forage diets of imperiled bumble bees can improve conservation planning and habitat restoration efforts. In this study, we describe the taxonomic composition of bee-collected pollen from 2 Rusty Patched Bumble Bee (Bombus affinis, Cresson) nests located in southeastern Minnesota. This is the first published reporting of pollen collected from active B. affinis nests. We also compared pollen identification via traditional palynological light microscopy with genetic identification via ITS metabarcoding. Among the 49 pollen samples analyzed, we detected 41 and 56 distinct taxa via light microscopy and metabarcoding, respectively. Furthermore, 27 of 47 total genera overlapped between the 2 methods. Bittersweet Nightshade (Solanum dulcamara, Linnaeus) was the most detected species for both metabarcoding and microscopy identification for pollen prevalence. Pollen volume from the microscopy data showed that Lesser Burdock (Arctium minus, Bernhardi), Alfalfa (Medicago sativa, Linnaeus), Bittersweet Nightshade (Solanum dulcamara, Linnaeus), Plumeless Thistle (Carduus acanthoides, Linnaeus), and Red Clover (Trifolium pratense, Linnaeus) together comprised more than half of the total volume of pollen. Light microscopy and metabarcoding revealed compositionally distinct plant communities when analyzed at the species level. Methodological concordance improved when analyzing pollen data at genus level, but both methods still reveal marginally distinct groupings. Our study highlights specific plant taxa that are important components of B. affinis pollen diets and provides actionable research for conservation efforts in urban systems. Our study also supports that B. affinis is a generalist forager and will collect pollen from a variety of native and non-native host plants.