A single mutation is driving resistance to pyrethroids in European populations of the parasitic mite, Varroa destructor

Varroa destructor is one of the major contributors to the significant losses of Western honey bee colonies worldwide. The synthetic pyrethroids tau-fluvalinate and flumethrin were very popular among beekeepers to control levels of parasitism until reports of therapeutic failures increased during the early 1990s. Three different mutations at position 925 of the V. destructor voltage-gated sodium channel have been associated with the resistance to these compounds. Resistant mites collected in the UK and in the Czech Republic showed only a substitution of leucine to valine (L925V), while those collected in the USA carried alternative mutations to isoleucine (L925I) or methionine (L925M). Here, we have used high-throughput genotyping assays to investigate the distribution of resistance mutations across Europe. Our data show that the mutation L925V is present in most of the European countries tested, albeit with an uneven distribution. We also show new evidence for the significant correlation of the mutation with resistance and conclude that it is likely that resistant mites have a reduced fitness. The implications for integrated management of the parasite are discussed.