Effects of CO2 elevation on life-history traits of two insecticide-resistant strains of planthopper Nilaparvata lugens on rice.

We made separate experiments to examine life-history traits and activities of protective enzymes as affected by carbon dioxide (CO₂) elevation to 780 μL/L as compared to 390 μL/L in imidacloprid- or buprofezin-resistant strains of the brown planthopper (BPH) Nilaparvata lugens. We found an interaction effect between resistance and the CO₂ level on the nymphal survival and duration in both resistant strains. Nymphal durations in both resistant strains were much shorter in the resistant than susceptible BPH at 780 μL/L but similar between them or slightly shorter in the resistant than susceptible BPH at 390 μL/L. Nymphal survival was lower for imidacloprid-resistant than its susceptible BPH at 390 μL/L but higher at 780 μL/L; it stayed unaffected by the CO₂ elevation in buprofezin-resistant BPH. We did not observe an interaction effect between resistance and the CO₂ level on major reproductive parameters in both resistant strains. But the 2 strains were not consistent across CO₂ levels in all parameters. Our measurements of protective enzyme activities of superoxide dismutase, catalase, and peroxidase showed an interaction between resistance and the CO₂ level. Overall, these enzymes became similar in activity between resistant and susceptible BPH at 780 μL/L compared to 390 μL/L and the change was more distinct in the imidacloprid- than buprofezin-resistant BPH strains. Our findings suggest that CO₂ elevation can affect life-history traits of insecticide-resistant BPH, while the effect may vary depending on the kind of insecticides it is resistant to.