Exposure to sublethal hexaflumuron delays development and reduces reproductive potential in the fall armyworm (Lepidoptera: Noctuidae) across generations

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae), is a major global pest whose management increasingly relies on insect growth regulators (IGRs) to mitigate resistance to conventional insecticides. This study evaluated the sublethal and transgenerational effects of hexaflumuron-a benzoylurea IGR-on FAW through a 2-generation laboratory bioassay. Newly molted third instars were exposed to diet-incorporated hexaflumuron, yielding LC10 and LC25 values of 0.485 and 0.898 mg L-1, respectively. Sublethal exposure reduced F0 pupal mass and decreased adult longevity and fecundity. Age-stage, two-sex life-table analysis was conducted for the untreated F1 offspring only and showed dose-dependent demographic costs. Offspring of exposed parents exhibited prolonged development (egg-to-adult period: 30.64 to 40.26 d at LC25), shorter adult lifespans (females: 10.33 to 8.00 d; males: 8.22 to 6.72 d), and reduced lifetime fecundity (1058.6 to 829.3 eggs female-1). Key population parameters declined, including net reproductive rate (R0: 508.1 to 273.7 offspring), intrinsic rate of increase (r: 0.176 to 0.123 d-1), and finite rate of increase (λ: 1.193 to 1.131 d-1), while mean generation time increased (T: 35.4 to 45.5 d). These results show that low-lethal hexaflumuron exposure imposes lasting demographic costs on FAW populations and highlight the importance of incorporating sublethal and transgenerational endpoints when integrating benzoylurea IGRs into FAW integrated pest management and resistance management programs.