From the field to the laboratory, investigating the effects of Deformed wing virus on honey bee health

Abstract

Varroa destructor is an ectoparasitic mite associated with significant losses of honey bee colonies globally. The mite vectors a range of pathogenic viruses, most notably Deformed wing virus (DWV). DWV is transmitted orally between generations of bees and by this route rarely causes symptomatic infection, but the introduction of Varroa alters the transmission route of the virus and leads to highly elevated virus titres. Annual overwintering colony losses of ~25% 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 continues unchecked. One of the aims of this study was to determine whether rational, coordinated treatment is beneficial to colony health. Over a period of three years, all colonies managed on the island of Arran were treated in unison. Changes in the mite levels and DWV levels and diversity were measured as indicators of changing colony health. Across the three years of analysis, total mite numbers decreased by 58% and the number of managed colonies increased by 50%. In parallel to the Arran study, a colony management technique – a shook swarm – combined with appropriate miticide treatments was shown to be highly effective in reducing mite infestations and DWV titres. The impact of no mite management was investigated by placing healthy colonies in a high-mite apiary and measuring their rates of mite uptake. This study indicated that mites rapidly enter the colonies, altering the DWV dynamic and typically resulting in colony death. A mite-virus-bee in-silico model, simulating the dynamic changes in the virus population across multiple generations of pupae was designed and recombination between two DWV variants was investigated to examine recombination junctions. These studies shed light on how Varroa-control and colony management techniques impact DWV levels and diversity and honey bee colony health.