Large‐Scale Monitoring, Biochemical Mechanism, and Fitness Cost of Resistance to Chlorfenapyr in a Near‐Isogenic Strain of Spodoptera litura (

ABSTRACT

Spodoptera litura is a globally important polyphagous herbivore that has developed resistance to many widely used insecticides. Chlorfenapyr is a pyrrole insecticide with demonstrated efficacy against lepidopteran pests, but the susceptibility baseline and field‐evolved resistance in S. litura remain poorly characterized. In this study, we built a near‐isogenic strain (JZ‐NIL) based on one field‐collected chlorfenapyr‐resistant population of S. litura and characterized patterns of cross‐resistance, fitness costs, and mechanism of metabolic resistance. In comparison with the susceptible Lab‐S strain, the field‐sampled JZ population displayed approximately 225.0‐fold resistance to chlorfenapyr. The JZ‐NIL strain was built and showed 124.2‐fold chlorfenapyr resistance, with no apparent cross‐resistance to broflanilide, chlorpyrifos, chlorantraniliprole, emamectin benzoate, indoxacarb, and spinetoram. Assays of enzyme activity and tests of synergism showed that diethyl maleate (DEM) made a synergistic ratio of 1.9 against chlorfenapyr, and glutathione S ‐transferase (GST) activity in JZ‐NIL was 1.8‐fold significantly higher than in the strain of Lab‐S, indicating that GST‐mediated metabolism contributes to chlorfenapyr resistance. In addition, pupation rate, fecundity, and hatchability were significantly lower in JZ‐NIL than in Lab‐S. The relative fitness of JZ‐NIL was 0.54 compared with Lab‐S. Overall, these results indicate that GST‐mediated detoxification contributes to chlorfenapyr resistance in S. litura and that this resistance is associated with significant fitness costs. Further studies are needed to clarify the metabolic and target‐site mechanisms underlying chlorfenapyr resistance.