Healthy Honey Bees – analysis of the Deformed Wing Virus population to assess rational Varroa control on a Scottish island

Varroa destructor is an ectoparasitic mite associated with significant losses of honey bee colonies globally. The mite vectors a range of pathogenic viruses, most important of which is Deformed Wing Virus (DWV, (+)ssRNA). Overwintering colony losses, accounting for the death of ∼25% of all colonies each year, are associated with high levels of Varroa-DWV infestation. Effective miticide treatments are available to control Varroa. However, the absence of coordinated treatment means environmental transmission of mites continued unchecked. We aim to determine whether rational, coordinated treatment is beneficial, using features of the DWV population as an indicator of colony health. This study uses coordinated treatment of Varroa in a geographically isolated environment (Isle of Arran, Scotland). It is reported that a high level of a near-clonal virus population is associated with Varroa infestation and colony losses, whereas Varroa-free healthy colonies carry only low levels of a diverse population of DWV. The study area contains 50-85 colonies and 25 beekeepers. Sampling and virus analysis – strain diversity and viral loads – have been conducted before and after treatment. Changes in virus diversity are quantified by next generation sequencing analysis to determine population diversity. In the first two years we have observed a geographic decrease in Varroa and changes in the composition of the virus population. This study will inform our development of rational Varroa control strategies for beekeepers in temperate regions and could be used to inform policy changes regarding treatment regimes in Scotland and elsewhere for this global pathogen.