Honey bee colony losses and associated viruses

•The terms ‘colony losses’ and ‘CCD’ are defined.•The existing correlative evidence for viruses as drivers of colony losses is evaluated.•Results from controlled infection experiments are critically reviewed.•Substantiation of previous findings on lethality of viruses by RNA interference is presented.•The role of V. destructor as mechanical and biological virus vector is explained.

Recent large-scale colony losses among managed Western honey bees (Apis mellifera) have alarmed researchers and apiculturists alike. Here, the existing correlative evidence provided by monitoring studies is reviewed which (i) identified members of the deformed wing virus and acute bee paralysis virus clades as lethal pathogens for entire colonies, and (ii) identified novel viruses whose impact on honey bee health remains elusive. Also discussed in this review is related evidence obtained via controlled experimental infection assays and RNAi approaches underscoring the damage inflicted by some of these viruses on individuals and colonies. The relevance of the ectoparasitic mite Varroa destructor acting as mechanical and biological virus vector for the enhanced virulence of certain viruses or mite selected virus strains is carefully considered.