Occurrence of honey bee-associated pathogens in Varroa-free pollinator communities.

Australia remains the last significant land mass free of Varroa, a parasitic mite which has caused dramatic honey bee (Apis mellifera) colony losses across the globe, due to its association with the pathogenic deformed wing virus (DWV). As such, Australia continues to maintain relatively healthy honey bee populations, despite recent work showing apiaries harbor a surprisingly high prevalence of microbial pathogens. We sought to determine the prevalence of these microbial pathogens in honey bees and native pollinators actively co-foraging on mass flowering crops and to understand the extent to which they may be shared between taxa. We found high prevalences of black queen cell virus (BQCV) and sacbrood virus (SBV) in the honey bees (88% and 41% respectively), and correspondingly, these were the most common honey bee pathogens detected in native pollinator taxa, albeit at much lower prevalence; the maximum prevalence for any pathogen in a native pollinator group was 24% (BQCV in Halictidae spp.). The viral pathogens Israeli acute paralysis virus and Lake Sinai viruses 1 and 2, and the fungal parasites Nosema apis and Nosema ceranae, were only rarely detected. Phylogenetic analyses of the most common pathogens revealed similar genotypes circulating between species. Our data suggest that, in Australian orchards, pathogen prevalence in honey bees is a good predictor of pathogen prevalence in native pollinators, which raises concerns about how the viral landscape may change in native taxa if, or when, Varroa arrives.