Effects of methoxyfenozide on the development, survival, and reproduction of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae)

The toxicity and sublethal effects of methoxyfenozide were evaluated in third instars of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) that fed on contaminated semisynthetic diet. The LC50 value was estimated at 0.23 mg of active ingredient [AI]/kg diet (range of 95% C.I.: 0.17–0.37) at 264 h after treatment. The effects on development, survival, and reproduction were observed in third instars of this pest that survived exposure to an LC25 concentration of methoxyfenozide. The larvae from the insecticide treatment exhibited lower pupal weights, an increase in both larval and pupal development times and a higher frequency of malformations of the wings in adults than untreated larvae. Adults from the methoxyfenozide treatment did not show reduced fecundity (mean cumulative number of eggs laid per female) but fertility as measured by the percentage of eggs hatched (fertility) was significantly reduced compared to untreated control insects. No significant effects were observed on pupal sex ratio. We concluded that the lethal and sublethal effects of methoxyfenozide are likely to have a significant impact on S. exigua populations on treated crops.