Physiological responses of young Italian worker bees (Apis mellifera ligustica Spin.) induced by different pollen diets

Abstract

Adequate pollen nutrition plays a crucial role in honey bee development and resilience to stressors. This study investigated the physiological responses of newly emerged Italian honey bee workers (Apis mellifera ligustica Spin.) to pollen diets collected at different times throughout the beekeeping season in a suburban area of Central Italy. The objective was to evaluate how variation in pollen composition and diversity influences key physiological traits and potential resistance to Vairimorpha spp. infection of workers. Corbicular pollen loads were collected every three weeks from March to August, and characterised through palynological, proximate, and mineral analyses. In-cage feeding trials were conducted over two weeks, evaluating daily intake, body composition (crude protein and lipid content), hypopharyngeal gland development, ovary maturation, and Vairimorpha apis and V. ceranae spore loads using RT-PCR and sequencing. Results showed that pollen collected during the central part of the season (April–June) had higher botanical diversity and nutrient content, particularly in proteins and key minerals (Mg, P, Cu, and Zn). Honey bees fed with these pollens exhibited greater development of hypopharyngeal glands, higher protein and lipid body reserves, and reduced relative Vairimorpha spp. spore loads compared to controls. Notably, pollen diets enhanced physiological development even when infection was present, suggesting a buffering effect of high-quality nutrition. These findings confirm the importance of seasonal pollen quality and diversity in sustaining bee health. Future studies should focus on experimental infections and compare mono- versus multifloral diets to better define nutritional strategies for beekeeping under changing environmental conditions