The effect of two distinct viral-enriched inocula on the immune response and chemical cues of honey bee pupae

The Varroa destructor (Varroa) and its vectored viruses are major drivers of honey bee ( Apis mellifera ) colony losses. Hygienic behavior, activated by olfactory cues from diseased brood, enables bees to cope with some pests and pathogens. In this study, we evaluated the effect of viral inoculation with varying doses of either deformed wing virus (DWV) B-A recombinant- or Israeli acute paralysis virus (IAPV) -enriched inoculum on pupal volatiles and immune response, independently of Varroa. Both inocula came from biological material commonly containing background levels of both viruses. Five days post-treatment, volatile profiles, viral loads, and expression of seven immune genes were assessed. IAPV-enriched inoculum caused dose-dependent mortality (up to 60%), while DWV-enriched inoculum caused limited mortality. All pupae injected with DWV-enriched inoculum exhibited high viral RNA levels of both DWV and IAPV, resulting in a DWV + IAPV co-infection, whereas pupae injected with the IAPV-enriched inoculum displayed high IAPV and dose-dependent DWV. Expression of immune genes was lower in pupae injected with IAPV-enriched inoculum-and lower immune gene expression than in the DWV+IAPV co-infected pupae, suggesting IAPV suppresses the immunity. Volatile profile of virus-injected pupae differed from controls. The ultimate consequence of such differences might lead to virus specific hygienic responses.