Abstract
Recent honey bee colony losses, particularly during the winter, have been shown to be associated with the presence of both ectoparasitic mites and Deformed Wing Virus (DWV). Whilst the role of Varroa destructor mites as a viral vector is well established, the role of Tropilaelaps mercedesae mites in viral transmission has not been fully investigated. In this study, we tested the effects that V. destructor and T. mercedesae infestation have on fluctuation of the DWV copy number and alteration of the virus variants in honey bees by characterizing individual pupae and their infesting mites. We observed that both mite species were associated with increased viral copy number in honey bee pupae. We found a positive correlation between DWV copy number in pupae and copy number in infesting mites, and the same DWV type A variant was present in either low or high copy number in both honey bee pupae and infesting V. destructor. These data also suggest that variant diversity is similar between honey bee pupae and the mites that infest them. These results support a previously proposed hypothesis that DWV suppresses the honey bee immune system when virus copy number reaches a specific threshold, promoting greater replication.
Highlights
Large-scale honey bee colony loss is increasingly being reported across North America and Europe (Goulson et al, 2015)
We examined pupae from capped brood cells that were infested with V. destructor and found that 100% were positive for Deformed Wing Virus (DWV) infection (30 out of 30)
Our results demonstrate that an increase in the V. destructor population of a colony enhances the prevalence of DWV infection in honey bee pupae, even in pupae without direct mite infestation
Summary
Large-scale honey bee colony loss is increasingly being reported across North America and Europe (Goulson et al, 2015). Many potential causes for the decline have been proposed, pathogens and parasites of honey bees, ectoparasitic mites are considered major threats to colony health (Evans and Schwarz, 2011; Goulson et al, 2015). One such mite species, Varroa destructor, is globally distributed (except Australia) and causes both abnormal brood development and brood death in honey bee colonies (Rosenkranz et al, 2010). These effects are elicited through mites feeding on hemolymph and by spreading honey bee viruses, Deformed Wing Virus (DWV) (de Miranda and Genersch, 2010; Martin et al, 2012)
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