Parasite-insecticide interactions: The impact of Nosema ceranae and fenpyroximate on honeybees (Apis mellifera)

[Display omitted] •Nosema ceranae and fenpyroximate have a synergistic effect on bees.•Long-term exposure to N. ceranae and fenpyroximate can reduce bee lifespan.•Fenpyroximate inhibits N. ceranae reproduction in the early stages, but N. ceranae develops resistance in later stages.•N. ceranae and fenpyroximate promote susceptibility and mortality in bees by affecting their antioxidant system. Honeybees are susceptible to parasitic infections. As a consequence, beekeepers often apply pesticides in their hives. This approach will also affect the health of bees while eliminating parasites. We used Nosema ceranae (2 × 107 spores/mL), 0.002 % fenpyroximate, and the combination of N. ceranae-fenpyroximate to respectively treat newly emerged worker bees, to assess their survival curve, spore number and the expression levels of genes related to oxidative stress in the midguts. As a result, chronic exposure to N. ceranae and/or fenpyroximate significantly decreased honeybee survival. However, there were no different effects between the N. ceranae and fenpyroximate treatments (P > 0.05). Fenpyroximate inhibited the reproduction of N. ceranae in the early stage, but the number of N. ceranae increased gradually in the later stage (P