Genetic Profile of the Parasitic Varroan Mite Varroa destructor (Arachnida: Mesostigmata: Varroidae) in Taiwan: a New Taiwanese Haplotype Intermediate Between the Highly Virulent Russian and Less Virulent Japanese Types Identified in the Honey Bee Host Apis cerana.

The Modern beekeeping industry is being challenged by the varroan mite and its transmitted pathogens. Various types of Varroa destructor exhibit different levels of virulence toward honey bees, but only the Japanese (J) and Russian (R) types were found to infect Apis mellifera. Type R was more highly virulent against A. mellifera in comparison with type J. Examining the genetic profile of Varroa species is therefore of crucial importance in apiary management. In this study, maternally inherited mitochondrial cytochrome oxidase I (COI) and bisexual nuclear internal transcribed spacer (ITS) sequences of V. destructor individuals from Taiwan were determined. All 168 COI sequences observed in populations obtained from A. mellifera were identical and belonged to type J, with one base difference to that of populations collected from A. cerana; the new type is named 'T type' (Taiwan type). ITS sequences of V. destructor and its sister species V. jacobsoni were identical. A network analysis based on 611 COI sequences compiled from references indicated the presence of 27 haplotypes in V. destructor. Epidemic history and relationship analyses of V. destructor showed that the basal haplotypes were those from A. cerana and many R-extending haplotypes infesting A. mellifera involving amino acid substitutions. Calibration dating based on COI analysis revealed that V. destructor differentiated from its sibling lineage (occurring in Sri Lanka) prior to 1.3 million years ago (Mya). The ancestral haplotype retention and drift in V. destructor that occurred locally during 0.10-0.64 Mya might be relevant to its host A. cerana, which had been isolated geologically. The highly virulent type R was spreading quickly and could gradually outcompete the common and less virulent type J. Type T, being intermediate between types R and J, ought to be studied to better understand the pathogenic mechanism of V. destructor in A. mellifera. Moreover, for areas where type R does not occur, such as Taiwan, quarantine requirements are crucial for reducing invasion risks.