Parallel evolution of Varroa resistance in honey bees; a common mechanism across continents?

The near-globally distributed ecto-parasitic mite of the Apis mellifera honey bee, Varroa destructor, has formed a lethal association with Deformed wing virus, a once rare and benign RNA virus. In concert the two have killed millions of wild and managed colonies, particularly across the northern hemisphere, forcing the need for regular acaricide application to ensure colony survival. However, despite the short association (in evolutionary terms), A. mellifera populations across the globe have been surviving many years without any mite control methods. This long-term survival, or Varroa resistance, is consistently associated with the same suite of traits, recapping, brood removal and reduced mite reproduction, irrespective of location. Here we conduct an analysis of data extracted from 60 papers to illustrate how these traits connect together to explain decades of mite resistance data. For the first time we have potentially a unified understanding of natural Varroa resistance that will help the global industry achieve widespread miticide free beekeeping and indicate how different honey bee populations across four continents have resolved a recent threat using the same suite of behaviours.

Methods
We searched the published literature for data on resistance traits for both susceptible and resistant honey bee colonies. In order to standardise the data, studies had to use natural comb and any infested cells contained only a single foundress mite. For recapping and brood removal data the number of cells examined by the study had to be greater than 50. Equally for mite non-reproduction data the sample sizes had to include at least 50 infested cells. Where possible single colony data was extracted from the studies. All recapping data (n = 163) came from single colonies; for brood removal nine of the 86 data points are colony averages; for mite infertility 75 of the 99 data points are colony averages, due to sample size limitations (see supplementary data for all source data).