Novel Insecticides and Viral Pathogens Do Not Synergistically Increase Honey Bee Mortality

This laboratory study examines the combined effects of sublethal doses of fipronil (FIP) and sulfoxaflor (SULF) insecticides and viral pathogens—deformed wing virus A/B (DWV-A/B) and black queen cell virus (BQCV)—on worker honey bee survival, viral load, and immunocompetence. Chronic exposure to FIP at 4.3 µg/ml (50% LC50) and SULF at 0.132 µg/ml (10% LC50), alongside viral injection at 10^7 titre, showed no synergistic increase in mortality or viral load. However, sulfoxaflor significantly modulated host immune responses, as indicated by altered gene expression. Fipronil reduced bee survival, and viral pathogens remained a key threat. The study concludes that co-exposure to FIP and SULF does not amplify viral pathogen impacts on honey bees.