Fitness Cost of Methoxyfenozide and the Effects of Its Sublethal Doses on Development, Reproduction, and Survival of Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)

In the present study, two experiments were designed to investigate the lethal and sublethal effects of methoxyfenozide on Spodoptera litura (F.). The first experiment was conducted to explore the fitness cost of methoxyfenozide resistance in a methoxyfenozide-resistant strain (selected with methoxyfenozide for 13 consecutive generations), leading to resistance ratio to methoxyfenozide 83.0- and 2359-fold higher when compared to the field and susceptible populations with a fitness cost of 0.17. In the second experiment, second instars of the susceptible strain were treated with sublethal doses of methoxyfenozide (LC30, LC20, and LC10) by diet incorporation for larval feeding for 3 days. It was observed that higher concentrations of methoxyfenozide significantly prolonged the larval and pupal development time of S. litura as compared to the control treatment. The number of eggs per female, egg hatching, sex ratio, and longevity of adults of methoxyfenozide-treated groups was greatly reduced as compared to untreated S. litura. Our data clearly indicated that fitness cost of methoxyfenozide and its sublethal effects on S. litura has an important impact on its population dynamics.