Shared pathogens among honey bees, wild bees and hoverflies in mountain ecosystems

This study investigates the prevalence, abundance, and drivers of bee-associated pathogens in honeybees, wild bees, and hoverflies (Syrphidae) across four National Parks in Northern Italy, encompassing diverse altitudinal and habitat gradients. Over 1,600 specimens from 54 species were analyzed to detect 10 bee-associated pathogens-including viruses, microsporidia, and trypanosomatids. Overall, 76.3% of individuals scored positive for at least one pathogen. Deformed wing virus (DWV) and chronic bee paralysis virus (CBPV) were the most prevalent pathogens, followed by Nosema ceranae and black queen cell virus (BQCV). Hoverflies harbored multiple pathogens, including sacbrood virus (SBV), detected exclusively in Syrphidae from three parks. Environmental factors significantly influenced infection risk, with pathogen prevalence decreasing at higher altitudes and with higher vegetation index values. Seasonality and host identity also influenced pathogen dynamics, with July showing a peak of pathogens' abundance and hoverflies exhibiting lower occurrence than bees. Among hoverflies, larval diet, voltinism, and sex were key predictors of the probability of pathogen occurrence and abundance. These findings highlighted extensive pathogen circulation in wild pollinators, even in mountain areas with limited anthropogenic pressure. The detection of bee pathogens in hoverflies underscores the need to broaden pollinator health surveillance and promote an integrated One Health approach for pollinator conservation.