Experimental viral spillover can harmBombus terrestrisworkers under field conditions

Abstract

AbstractDeformed wing virus (DWV), notorious for its virulence in the western honey bee (Apis mellifera)when vectored by the ectoparasitic miteVarroa destructor, is also widespread among wild bumble bee species, presumably through spillover from honey bees. Experimental studies on the virulence of DWV inBombusspp. have provided equivocal results and have until now been confined to bumble bees under laboratory conditions.Here, we inoculated commercially rearedBombus terrestrisworkers with DWV‐A through feeding or injection and introduced them into experimental colonies placed in the field, thus exposing them to the environment and associated stressors. We monitored the survival of inoculated worker bumble bees and quantified their viral load at 10 days post inoculation.Bombus terrestrisworkers injected with DWV‐A supported high viral loads and exhibited significantly reduced median survival compared to controls. Bumble bees inoculated by feeding had low or zero detectable viral loads while their mortality did not differ from the control group.Our results demonstrate that, although DWV‐A is pathogenic for commercialB. terrestris, the risks for individual fitness from spillover of DWV‐A during foraging on shared flowers appear limited.The findings of this experiment also highlight the necessity to address the potential context‐dependence of virulence when evaluating the impact of a pathogen in an alternative host.