Pollen nutrition shapes demographic performance and gene expression in a bumblebee (Bombus eximius)

Bumblebees (Bombus spp.) are essential pollinators in a wide range of ecosystems, including agricultural systems. Addressing the critical knowledge gap in species-specific nutritional requirements, which leads to inconsistent colony development in native bumblebees like Bombus eximius, this study investigated the effects of pollen diet on microcolony development and reproduction. We examined the effects of three monofloral pollen diets, namely, Brassica napus, Camellia sinensis, and Zea mays, on worker egg-laying, drone larval development, lifespan, and gene expression. Our findings revealed that pollen nutritional quality significantly affected reproductive output, including the preoviposition period (time to first egg) and oviposition periods (duration of egg-laying), as well as offspring development in bumblebees. Worker bees fed C. sinensis and B. napus pollen exhibited significantly higher expression of the vitellogenin (encoding a yolk protein precursor crucial for oocyte development and egg production) and hexamerin (encoding a major storage protein vital for development and amino acid reserves) genes in their abdomens than did those fed Z. mays pollen. Microcolonies fed C. sinensis pollen demonstrated the highest reproductive success, the shortest mean semi-generation time, and the longest lifespan, indicating its superior nutritional quality for B. eximius. These results highlight the critical role of pollen nutrition in bumblebee health and suggest that C. sinensis pollen could enhance the performance of managed bumblebee colonies.