Virome compositions indicate that viral spillover is a dead-end between the western honey bee and the common eastern bumblebee

The potential of viral spillover from the western honey bee (Apis mellifera) to other insects is well established. New variants should inevitably emerge following a host expansion, yet to our knowledge no study has shown this within this system. To investigate the outcome of viral spillover, we sequenced the meta-transcriptomes of sympatric A. mellifera (n = 389) and common eastern bumblebee Bombus impatiens (n = 117) over three years. Distinct viromes occurred within each bee species throughout the study duration, with honey bee viruses forming a minor fraction of the bumblebee virome. Viruses shared by both bees shared over 98 % nucleotide identity, and no bumblebee-specific strains of honey bee viruses occurred, as expected if spillover led to a true host expansion involving bumblebee-bumblebee transmission. We conclude that the honey bee viruses, namely deformed wing virus, black queen cell virus, and sacbrood virus, were present in the bumblebees due to environmental exposure or dead-end spillover, and not spillover host expansion.