Unravelling the Interplay Between Vairimorpha ceranae and Viruses in Geographically Isolated Honey Bee (Apis...

Viral infections and the microsporidian Vairimorpha ceranae ('vairimorpha') have been involved in elevated honey bee (Apis mellifera) colony losses as a result of their individual or combined actions, with the ectoparasitic mite Varroa destructor ('varroa') often exacerbating these effects. This study investigates the relationship between vairimorpha and several common honey bee viruses within the unique ecological context of the remote mid-Atlantic Azores archipelago, which comprises three main islands where varroa is present and six islands where varroa is still absent. We sampled 494 colonies across these islands and employed RT-qPCR to detect and quantify vairimorpha and nine common honey bee viruses, of which seven were detected. The data were modelled using a Bayesian approach, which estimated the likelihood of an effect of the presence of vairimorpha on the loads of each of the viruses on varroa-infested and varroa-free islands. Both vairimorpha and the seven bee viruses were differentially distributed among the islands. An additive relationship was found between vairimorpha and both black queen cell virus (BQCV) and Lake Sinai virus (LSV), the latter driven almost exclusively by one strain (LSV-2), and this relationship was stronger on the varroa-infested islands (Pr = 96.2%) than on the varroa-free islands (Pr = 69.1%). No association was found between vairimorpha and the two main strains of DWV (DWV-A and DWV-B) across all islands, although an antagonistic relationship may exist between vairimorpha and the rare DWV-C strain, found only on varroa-free islands. This study supports previous findings and shows the importance of possible additive relationships among co-infecting honey bee pathogens and parasites.