"Pollen diets influence gut microbiota composition and colony development in native South American bumblebees"

Bumblebees are excellent pollinators sustaining ecosystems, however, their populations are declining due to land-use changes, lack of food resources, and pathogen-induced diseases. The gut microbiota is central to animal health, influencing nutrition and defense. We examined how pollen diet affects colony development, pathogen presence, and gut microbiota in two native South American bumblebee species, Bombus pauloensis and B. bellicosus. In B. pauloensis, monofloral pollen from Eucalyptus grandis increased worker body mass and showed a slight reduction in developmental time compared to polyfloral pollen. In B. bellicosus, no significant diet effects on body mass or development time were observed. Diet also altered gut microbiota structure. Based on diversity analyses, significant diet-associated shifts were observed in B. pauloensis queens and B. bellicosus workers. In B. pauloensis queens, monofloral pollen increased bacterial richness and favored Snodgrassella spp., whereas in B. bellicosus workers, monofloral pollen also increased diversity, but enriched ASVs were mainly environmental taxa. The microsporidian pathogen Nosema ceranae was detected in a single B. pauloensis colony, limiting conclusions about prevalence or diet. These findings demonstrate that nutritional quality of dietary pollen and/or pollen diversity modulates gut microbiota and colony development in native bumblebees, with species and caste-specific responses. Our study suggests a potential role of nutrition in host-microbiota interactions and indicates that agricultural intensification and the loss of floral diversity may affect bee health. By linking pollen nutritional quality/diversity, microbiota structure, and colony performance, these findings may help inform pollinator-friendly landscape management and could contribute to improving the resilience of South American agroecosystems.