Virus infections in Varroa destructor-resistant honeybees
Populations of European honeybee subspecies, Apis mellifera, have the ability to adapt naturally to the ectoparasitic mite, Varroa destructor. It is possible that a tolerance to mite-vectored viruses may contribute to colony survival. If this is the case, surviving populations should show lower virus titers and prevalence compared to susceptible populations. Here, we investigated the prevalence and titers of 10 viruses, some known to be associated with V. destructor, in adult workers and pupae as well as mites. Samples were collected from both a mite-surviving and mite-susceptible honeybee population in Norway. Surviving colonies had a lower prevalence of a key virus (DWV-A) associated with V. destructor in individual adult bees sampled, and generally lower titers of this virus in mite infested pupae and mites within the colonies when compared to sympatric, susceptible controls. However, these surviving colonies also displayed higher prevalence and titers of two viruses not associated with V. destructor (BQCV & LSV1). The results of this study therefore suggest that general tolerance to virus infections is unlikely to be a key mechanism for natural colony survival in Norway, but evidence may point to mite control as a predominant mechanism.