Nutritional profiling of common eastern North American pollen species with implications for bee diet and pollinator health

Urbanization, agriculture, and climate change have known negative impacts on global bee populations, but malnutrition as a result of disrupted or altered floral resources also hinders bee survivorship. Hence, understanding the nutritional content of pollen—the main source of protein, minerals, and lipids required by bees—is paramount to capture the requirements of a balanced diet to support bee health. Here, we characterize the non-esterified fatty acid (NEFA) and amino acid (AA) content of 22 pollen species from 11 families commonly found in eastern North America, to assess their nutritional profile and importance to bee diet. We found that total NEFA content was highly variable across pollen families and genera, but essential fatty acids omega-6 and omega-3 were the most abundant across the majority of pollen species. Total AA content was also diverse across pollen families and genera, and the presence of ten essential amino acids was detected in all pollen species (except for methionine in Rhus glabra). P:L ratios ranged broadly from 2.9 in Trifolium sp. to 74.4 in Prunus sp., but omega-6:3 ratios were generally below one for the majority (73%) of studied pollen species. Phylogenetic comparisons detected a significant negative correlation between essential AA against total NEFA and total omega content, suggesting potential trade-offs with lipid and essential AA in pollen nutrition. Our findings suggest that multiple pollen species have the potential to be considered a valuable source of protein and lipid, and that a diversity of flora is essential to meet diverse bee diet and nutritional needs.