A nutritionally complete pollen-replacing diet protects honeybee colonies during stressful commercial pollination-requirement for isofucosterol.

A steady supply of nutritionally adequate pollen from diverse flower sources is crucial for honeybee colonies. However, climate instability, large-scale agriculture and the loss of flower-rich landscapes have made this supply scarce and unpredictable, threatening both apiculture and sustainable crop pollination. We developed a nutritionally complete pollen-replacing diet that supports continuous brood production from May to October in colonies without access to pollen. Omitting isofucosterol, the third most abundant sterol in honeybees, causes significant reductions in brood production and neuromuscular dysfunction in adults, identifying isofucosterol as a critical micronutrient. In contrast, omitting 24-methylene cholesterol-the most abundant honeybee sterol-does not significantly affect brood production, and surprisingly, bees remain viable without it. Colonies fed a commercial diet severely declined in brood production after 36 days and died out. In a season-long experiment investigating the commercial pollination of blueberry and sunflower fields, a treatment group fed the complete diet overcame the detrimental effects of nutritional stress, unlike colonies in 'No Diet' and 'Commercial Diet' groups. This study suggests that feeding a complete, pollen-replacing diet to nutritionally stressed colonies can address the root causes of honeybees' growing nutritional deficiencies, supporting their health and their vital pollination services.