Abstract:  【Aim】 To clarify the effects of broflanilide on the fitness and detoxification enzyme activities of Spodoptera frugiperda after multiple generations of selection and to provide a theoretical basis for the scientific and rational use of this insecticide. 【Methods】 The changes in the toxicity of broflaniliole to the 3rd instar larvae, the activities of detoxification enzyms (cytochrome P450 monooxygenase, glutathione S-transferase and carboxylesterase) in the 3rd instar larvae and the population fitness of S. frugiperda were determined after the newly hatched larvae were continuously exposed to 0.25 mg/L of broflanilide for 10 generations by the diet-overlay method. And the synergistic effects of three synergists (PBO, TPP and DEM) on broflanilide were determined in bioassay against the 3rd instar larvae of S. frugiperda. 【Results】 After 10 generations of selection by broflanilide, the exposed S. frugiperda population Bro-SEL developed 2.71-fold resistance to broflanilide, compared to the unexposed population UNSEL. At the same time, the fecundity and larval survival rate of the exposed population Bro-SEL were significantly decreased and the population parameters (intrinsic rate of increase, finite rate of increase and net reproductive rate) were also significantly decreased, as compared to those in UNSEL. The Bro-SEL population had the relative fitness of 0.35. The carboxylesterase activities in the 3rd instar larvae of Bro-SEL were significantly increased by 1.62- and 1.61-fold, respectively, when using α-NA and β-NA as the substrates, but the activities of cytochrome P450 monooxygenase and glutathione S-transferase in the 3rd instar larvae of Bro-SEL had no significant change as compared with those in the unexposed population UNSEL. Bioassay against the 3rd instar larvae of S. frugiperda revealed that both PBO and TPP had significant synergistic effects on broflanilide, with the synergistic ratios of 1.31 and 1.42, respectively.【Conclusion】 These results showed that there was little change in the toxicity of broflanilide to S. frugiperda population after 10 generations of selection by the insecticide broflanilide, indicating that S. frugiperda has a low risk of metabolic resistance to broflanilide, but the population development and reproduction of S. frugiperda have high fitness cost, and broflanilide is a good alternative agent for controlling S. frugiperda.

Key words: Spodoptera frugiperda, broflanilide, fitness, detoxification enzyme, pesticide resistance