Molecular analysis of voltage-gated sodium channels to assess τ-fluvalinate resistance in Japanese populations of Varroa destructor (Acari: Varroidae)

The pyrethroid τ-fluvalinate is widely used to control Varroa destructor Anderson and Trueman (Acari: Varroidae), a pest mite that can cause colony loss for the western honey bee Apis mellifera Linnaeus (Hymenoptera: Apidae). However, τ-fluvalinate resistance has been reported in V. destructor populations worldwide, and mutations in voltage-gated sodium channels (VGSCs) at L1002 (equivalent to L925 in the house fly) are thought to be a major cause. τ-fluvalinate is commonly used in Japanese apiaries for controlling V. destructor; however, a detailed investigation of VGSC mutation(s) has not been yet conducted. The polymerase chain reaction-restriction fragment length polymorphism (PCR–RFLP) analysis is used to detect VGSC mutations. Because Varroa mites are haplodiploid with sib-mating, the inbred offspring of heterozygote mothers could be L925 homozygotes. In this study, we optimized PCR–RFLP with two sets of primers to detect L925 alleles precisely. The method could detect L925 homo- and heterozygotes in the Varroa mites in Japanese apiaries. The sequencing of PCR amplicons confirmed these mites had an L925M mutation, which has been reported to cause τ-fluvalinate resistance. Our report of incidences of the L925M mutation suggests that some mites may be resistant to this pyrethroid. (190/200 words)