Do not compromise: Nurse honeybees practice strict protein-lipid regulation.

The Nutritional Geometry Framework (NGF) has been instrumental in revealing how animals regulate nutrient intake. In honeybees (), most research has emphasized protein-carbohydrate regulation, even though pollen is rich in both protein and lipid. We used NGF-based no-choice and choice experiments to examine how nurse bees, responsible for brood care, regulate protein and lipid intake. Bees consumed the most and developed the largest hypopharyngeal glands on diets with 30% protein and 20% lipid. When given dietary options, they regulated intake toward this 1.5:1 protein-lipid ratio. Feeding typically stopped once either a protein or lipid threshold was reached, consistent with a "strict restraint" rule that may reflect physiological costs of even slight overconsumption. These findings underscore the importance of protein-lipid regulation in nurse bees. This work broadens understanding of nutrient regulation in animals that consume protein- and lipid-rich foods and highlights the importance of diet quality for bee health.