Abstract: 【Aim】 This study aims to compare the effects on the toxicities of chlorfenapyr and tolfenpyrad and the activities of their protective enzymes, detoxifying enzymes and so on in Frankliniella occidentalis and F. intonsa adults under different CO₂ concentrations, so as to provide guidance for the resistance management of thrips to chlorfenapyr and tolfenpyrad under elevated CO₂ and timely adjustment of pest management strategies. 【Methods】 The toxicities ［medium lethal concentration (LC₅₀ value) and sublethal concentration (LC₂₅ value)］ of chlorfenapyr and tolfenpyrad to adults of the two thrips under the ambient CO₂ concentration (400 μL/L) and the elevated CO₂ concentration (800 μL/L) were determined by dipping method. The activities of protective enzymes ［superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT)］, detoxifying enzymes ［carboxylesterase (CarE), glutathione S-transferase (GST) and cytochrome P450 enzyme system (CYP450)］ and acetylcholine esterase (AChE) in adults of the two thrips exposed to LC₂₅ of chlorfenapyr and tolfenpyrad for 48 h under the two CO₂ concentrations were determined with enzymatic activity assay. 【Results】 The LC₅₀ values of chlorfenapyr against F. occidentalis and F. intonsa adults in 48 h under the 800 μL/L CO₂ concentration were 1.33 and 0.37 mg/L, respectively, which were 0.68 and 0.66 times those under the 400 μL/L CO₂ concentration, respectively. The LC₂₅ values of chlorfenapyr against F. occidentalis and F. intonsa adults in 48 h under the 800 μL/L CO₂ concentration were 0.60 and 0.24 mg/L, respectively, which were 0.61 and 0.83 times those under the 400 μL/L CO₂ concentration, respectively. The LC₅₀ values of tolfenpyrad against F. occidentalis and F. intonsa adults in 48 h under the 800 μL/L CO₂ concentration were 1 002.64 mg/L and 247.66 mg/L, respectively, which were 0.98 and 0.78 times those under the 400 μL/L CO₂ concentration, respectively. The LC₂₅ values of tolfenpyrad against F. occidentalis and F. intonsa adults in 48 h under the 800 μL/L CO₂ concentration were 368.77 and 146.10 mg/L, respectively, which were 2.44 and 1.21 times those under the 400 μL/L CO₂ concentration, respectively. The activities of the tested enzymes (except CYP450) in adults of both thrips exposed to LC₂₅ of chlorfenapyr and tolfenpyrad for 48 h under the 800 μL/L CO₂ concentration were higher than those under the 400 μL/L CO₂ concentration, and the activities of SOD, POD, CAT and AChE in F. occidentalis adults were significantly higher than those in F. intonsa adults under the two CO₂ concentrations. Under the two CO₂ concentrations, the activities of protective enzymes (except SOD in F. intonsa under 400 μL/L CO₂) in adults of both thrips exposed to LC₂₅ of tolfenpyrad were significantly higher than those in the control (treatment with distilled water containing 0.1% Tween-80), and the activities of SOD and CAT in F. occidentalis adults were the highest, being 39.74±1.59 and 37.93±1.31 U/mg pro, respectively. After being exposed to LC₂₅ of chlorfenapyr and tolfenpyrad for 48 h under the two CO₂ concentrations, the CarE activities in F. occidentalis adults were significantly decreased, while those in F. intonsa adults increased as compared to those in the control, with significant difference after treatment with tolfenpyrad, the AChE activities in adults of both thrips were significantly enhanced as compared to those in the control under the two CO₂ concentrations. 【Conclusion】 Elevated CO₂ directly enhances the efficacy of insecticides to F. occidentalis and F. intonsa, while F. intonsa is more susceptible to these two insecticides than F. occidentalis, and F. occidentalis shows stronger adaptability to these two insecticides than F. intonsa.

Key words: Frankliniella occidentalis; Frankliniella intonsa, climate change, carbon dioxide, chlorfenapyr, tolfenpyrad, enzymatic activity