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

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 x 10(7) 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 < 0.01). Furthermore, the expression levels of genes related to oxidative stress were constantly changing with time under different treatments. In particular, the expression of the catalase gene was upregulated, and that of the ROS modulator 1 -like gene and the superoxide dismutase gene was downregulated. In conclusion, this study indicated that the negative impact of N. ceranae and/or fenpyroximate on the health of honeybees caused the activation of their antioxidant system. Moreover, the redox status of the bees could increase their susceptibility and mortality.