Host shifts of parasites are often causing devastating effects in the new hosts. The Varroa
genus is known for a lineage of Varroa destructor that shifted to the Western honey bee,
Apis mellifera, with disastrous effects on wild populations and the beekeeping industry.
Despite this, the biology of Varroa spp. remains poorly understood in its native distribution
range, where it naturally parasitizes the Eastern honey bee, Apis cerana. Here, we combined
mitochondrial and nuclear DNA analyses with the assessment of mite reproduction to determine
the population structure and host specificity of V. destructor and Varroa jacobsonii in
Thailand, where both hosts and several Varroa species and haplotypes are sympatric. Our
data confirm previously described mite haplogroups, and show three novel haplotypes.
Multiple infestations of single host colonies by both mite species and introgression of alleles
between V. destructor and V. jacobsonii suggest that hybridization occurs between the two species.
Our results indicate that host specificity and population genetic structure in the genus
Varroa is more labile than previously thought. The ability of the host shifted V. destructor
haplotype to spillback to A. cerana and to hybridize with V. jacobsonii could threaten
honey bee populations of Asia and beyond.