Biogeographic patterns of host specificity in Thai Varroa jacobsoni

The environmentally varied mainland and peninsular regions of Thailand serve as home to a range of genetically distinct mtDNA lineages of the honey bee mite Varroa jacobsoni. These subpopulations coincide geographically with subpopulations of their natural host, Apis cerana. Here we investigated whether the sharp mite distribution boundaries are based on barriers to mite reproduction in non-native colonies of A. cerana. Mites from Northern Thailand were manually introduced to A. cerana colonies from south of the Kra Ecotone and vice versa during the peak of drone production. Upon completion of the normal Varroa reproduction cycle all capped drone brood with adult mites and their juveniles was collected from the experimental colonies. DNA was extracted from mites and analyzed for specific diagnostic haplotypes to test for reproduction of mites that were transferred to colonies of the different population. Several reproductive events of non-native mites were identified in each experimental colony. Thus, no conclusive evidence for the predicted, absolute reproductive barriers was discovered and we conclude that the parallel distribution of mtDNA lineages of V. jacobsoni and A. cerana in Thailand can mostly be explained by their corresponding biogeographic history. However, we cannot exclude quantitative or long-term resistance effects, such as offspring sterility, and climatic selection on the adult dispersal stage as explanatory causes of the distribution of this agriculturally significant species of mite.