Variable infections but no evidence of immune priming in bumble bee hosts against novel exposure to a honey bee virus

Ongoing global change presents novel challenges to species persistence, including heightened emerging infectious disease (EID) exposure. While invertebrates lack vertebrate acquired immunity, many species exhibit “immune priming” with enhanced protection to repeated pathogen exposures. This phenomenon could be critical for species of conservation concern, such as for wild bumble bees, where EID risk is amplified through contact with managed bee pollinators. We investigate the potential for immune priming against the honey bee-derived Israeli Acute Paralysis Virus (IAPV) in Bombus impatiens bumble bees. We test the hypothesis that prior pathogen-associated exposure affords greater resistance and tolerance upon secondary pathogen exposure, due to the adaptive benefits of immune plasticity. However, we find no evidence from viral infection levels or survival for either specific or general priming from low dose or inactivated virus, or synthetic viral RNA constructs. Infection levels, however, show patterns indicative of immune senescence and an intriguing bimodal distribution that warrants further investigation. Our results indicate that antiviral immune priming in bumble bees may be limited in capacity against viral spillover and utility for strategic conservation interventions. They also contribute to our growing understanding that beneficial immune priming is not a universal phenomenon across or even within invertebrate host taxa.