Abstract

Flubendiamide, a diamide insecticide, is widely used for controlling the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae). This study evaluated the resistance risk, associated fitness costs, and underlying metabolic mechanisms of flubendiamide resistance in FAW. After 20 generations of laboratory selection, FAW developed a 22-fold increase in resistance, with a realized heritability ( h 2 ) of 0.099. Compared with the unselected strain (UN-SEL, F0), the flubendiamide-selected populations (Flu-SEL, F10 and F20) exhibited significantly prolonged larval (1st-6th instars) and pupal developmental times, extended total pre-oviposition period (TPOP) and mean generation time ( T ), and reduced pupal weight, fecundity, and egg hatchability. Biochemical assays revealed elevated activities of cytochrome P450 monooxygenases (P450), carboxylesterases (CarE), and glutathione S-transferases (GST) in the Flu-SEL populations. Synergist assays further indicated that the P450 inhibitor piperonyl butoxide (PBO) significantly enhanced flubendiamide toxicity in the Flu-SEL (F20) population. Transcriptome analysis identified 3292 differentially expressed genes (DEGs) between Flu-SEL (F10/F20) and UN-SEL (F0) populations, including multiple detoxification-related genes. These findings provide new insights into the molecular basis of flubendiamide resistance in FAW and offer critical information for the development of more effective insecticide resistance management strategies.