Condition-dependent virulence of Slow Bee Paralysis Virus in Bombus terrestris: Are the impacts of honeybee viruses in wild pollinators underestimated?
© The Author(s) 2017. Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Slow Bee Paralysis Virus (SBPV) - previously considered an obligate honeybee disease – is now known to be prevalent in bumblebee species. SBPV is highly virulent in honeybees in association with Varroa mites, but has been considered relatively benign otherwise. However, condition-dependent pathogens can appear asymptomatic under good, resource abundant conditions, and negative impacts on host fitness may only become apparent when under stressful or resource-limited conditions. We tested whether SBPV expresses condition-dependent virulence in its bumblebee host, Bombus terrestris, by orally inoculating bees with SBPV and recording longevity under satiated and starvation conditions. SBPV-infection resulted in significant virulence under starvation conditions, with infected bees 1.6 times more likely to die at any given time point (infected bees die a median of 2.3 hours earlier than uninfected bees), whereas there was no effect under satiated conditions. This demonstrates clear condition-dependent virulence for SBPV in B. terrestris. Infections that appear asymptomatic in non-stressful laboratory assays may nevertheless have significant impacts under natural conditions in the wild. For multi-host pathogens such as SBPV, the use of sentinel host species in laboratory assays may further lead to the underestimation of pathogen impacts on other species in nature. In this case the impact of ‘honeybee viruses’ on wild pollinators may be underestimated, with detrimental effects on conservation and food security. Our results highlight the importance of multiple assays and multiple host species when testing for virulence, in order for laboratory studies to accurately inform conservation policy and mitigate disease impacts in wild pollinators.
This work was funded by a Royal Society Dorothy Hodgkin fellowship to LW and a NERC studentship to RM. We would like to thank Jess Lewis and Katherine Roberts for help with the experiment, Devi Newcombe, Caroline Moussy, Corrina Lowry, John Hunt and Bryony Williams for assistance in the lab, Ken Haynes and group for the use of their lab and equipment, and Elze Hesse and James Cresswell for statistical advice.
This is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this record.
Published online 30 March 2017