Transmission of Kashmir bee virus by the ectoparasitic mite Varroa destructor

The ability of the parasitic mite Varroa destructor to transmit Kashmir bee virus (KBV) to the Western honey bee (Apis mellifera) was investigated by exposing pupae from a KBV-negative colony to varying numbers of adult female mites from KBV-positive colonies. After five days, the virus status of pupae and the mites was determined by RT-PCR. There was a significant relationship between KBV-positive pupae and exposure to KBV-positive mites. No pupae were virus-positive when all the mites introduced into a given cell subsequently tested negative. Mites testing positive for KBV transmitted virus about 70% of the time. The percentage of KBV-positive V. destructor in a given cell also increased significantly, suggesting virus-free mites became virus-positive by cohabiting in the same cell with virus-positive mites, and we calculated the mite-to-mite transmission rate as 51%. There was 100% sequence identity of 415 bp KBV fragment amplified from bee pupae and mites, reflecting two isolates of the same virus source and supporting the conclusion of virus transmission from mite to bee pupae.