Host switch by honey bee parasitic mites leads to symbiont diversification

Host-parasite co-evolution is a reciprocal genetic change; however, the parasite may switch to a novel host, deviating from conventional co-evolution. Varroa destructor is a native parasite of the honey bee Apis cerana, and the mite has established infestation in another honey bee, Apis mellifera, causing colony failure. When mites switched to the novel host, they formed a distinct population from mites that remained on the native host. Consequently, this led to divergence in the microbiota associated with mites in two host populations. The microbes were conserved at the species level reflected by alpha diversity, with substantial relative abundance variance. Microbes found in mites were distinct from the bee microbiota. They mainly were pathogenic with antibiotic resistance, while a few bacterial taxa were previously found in honey bees, including Klebsiella pneumoniae and Pseudomanas aeruginosa. These symbionts may transfer between the mites and honey bees.