Fine scale population genetic structure of Varroa destructor, an ectoparasitic mite of the honey bee (Apis mellifera)

Varroa destructor is an obligate ectoparasitic mite and the most important biotic threat currently facing honey bees (Apis mellifera). We used neutral microsatellites to analyze previously unreported fine scale population structure of V. destructor, a species characterized by extreme lack of genetic diversity owing to multiple bottleneck events, haplodiploidy, and primarily brother-sister matings. Our results surprisingly indicate that detectable hierarchical genetic variation exists between apiaries, between colonies within an apiary, and even within colonies. This finding of within-colony parasite diversity provides empirical evidence that the spread of V. destructor is not accomplished solely by vertical transmission but that horizontal transmission (natural or human-mediated) must occur regularly.