International Union for the Study of Social Insects (IUSSI2018), August 5-10, 2018 in Guarujá, Brazil.

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Vector-mediated viral transmission weeds out virulent viruses

Author(s):
Madeleine Beekman, Emily Remnant , Niklas Mather , Thomas L. Gillard , Boris Yagound
Institution(s):
Behaviour and Genetics of Social Insects Laboratory, School of Life and Environmental Sciences, The University of Sydney; Behaviour and Genetics of Social Insects Laboratory, School of Life and Environmental Sciences, The University of Sydney ; Behaviour and Genetics of Social Insects Laboratory, School of Life and Environmental Sciences, The University of Sydney ; Behaviour and Genetics of Social Insects Laboratory, School of Life and Environmental Sciences, The University of Sydney ; Behaviour and Genetics of Social Insects Laboratory, School of Life and Environmental Sciences, The University of Sydney
While it is obvious that the ectoparasitic mite Varroa destructor is largely responsible for the widely-reported demise of the Western honeybee Apis mellifera, the exact role the mite plays in honeybee health remains unclear. The last few years have seen a surge in studies associating RNA viruses vectored by the mite with the death of honeybee colonies. Varroa potentially facilitates the spread of RNA viruses because it feeds on developing bee brood and injects haemolymph from bee-to-bee. Such change in transmission, from horizontal and vertical to vector-based, is predicted to lead to an increase in virulence of RNA viruses, thus potentially providing an explanation for the observed association between Varroa and certain viruses. Here we document the effect of changing the route of transmission of honeybee viruses contained in the haemolymph of honeybee pupae. We find that a change in mode of transmission rapidly increases viral titres of two honeybee viruses, Sacbrood virus (SBV) and Black Queencell virus (BQCV). This increase in viral titre is accompanied by an increase in virulence. In contrast, the virus most often associated with Varroa, Deformed Wing Virus, shows a reduction in viral titre in the presence of SBV and BQCV. In addition, DWV does not cause mortality in isolation. Most likely a change in mode of transmission due to the arrival of a vector quickly eliminates the most virulent honeybee viruses resulting in an association between Varroa and more benign viruses such as DWV. Our work therefore provides a novel explanation for the widely observed association between Varroa and DWV.
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