Nutrition of honeybees is constrained by the ratios of essential amino acids in pollen protein

Bees pollinate most of the world's flowering plants and collect and eat floral pollen as their sole source of dietary protein, yet we know relatively little about nutritional constraints imposed on them by pollinivory. Pollen protein provides bees with essential amino acid (EAA) profiles that vary as a function of plant species, but the extent of this variation and its impact on bee feeding behaviour and performance are unknown. Here, we measured the EAA profiles of pollen, bee bread, honeybees, and royal jelly to understand natural variation in protein quality and tested how mismatches in EAAs relative to bee tissues impacted protein-to-carbohydrate regulation in adult workers. Bees fed diets with an EAA profile that matched their own tissues consumed more food, gained more weight, and ate proportionally more protein relative to carbohydrate (1:72 EAA:C) while those fed with pollen sources including bee bread ate proportionally less protein and less food overall. Deficiencies found in pollen led us to discover that nutrient balancing for protein and carbohydrate in bees was driven by the inverse relationship between quantities of the branched-chain amino acids relative to histidine in dietary protein. We predict that the creation of bee bread, a mixture of bee-collected pollen, is a general adaptation to pollen feeding that reduces the impact of imbalances in the EAA profile of pollen protein.