D3063: Japanese orchard bees (Osmia cornifrons) face fitness consequences when pollen diets are too high in protein

Japanese orchard bees (Osmia cornifrons) are used as primary pollinators for fruit tree production in the northeastern United States. Wood edges and pollinator strips are used to supplement forage for wild bees when fruit trees are not in bloom, but little is known about dietary requirements for O. cornifrons. Here, we sought to determine if pollen diet diversity or protein to lipid ratio (P:L) are more important for O. cornifrons success. We hypothesized that P:L ratio would be more important than diversity due to similar findings in eusocial bee species. O. cornifrons larvae were collected from trap nests in central Pennsylvania and transferred to new pollen diets in the lab. Diets consisted of pollen from single plant species of different P:Ls or multifloral pollen diets altered to have different P:Ls. We found that larvae tolerated P:L ratios from single plant and multifloral diets between 2.4:1- 9:1. There were no significant differences in larval survival between single plant and multifloral diets, appearing to indicate that P:L ratio is more important than pollen diversity. However, bees that consumed higher protein diets within this range gained less mass than other dietary treatment groups throughout development. This suggests that there is a fitness consequence, but not a mortality consequence, for individuals that consume too much protein.