Toxicity of selected insecticides to fall armyworms (Lepidoptera: Noctuidae) in laboratory bioassay studies

Efficacy of conventional and experimental insecticides against the fall armyworm, Spodoptera frugiperda (J. E. Smith), was evaluated in laboratory bioassays. In a laboratory diet bioassay, third instars of a laboratory-strain were more susceptible to novel insecticides, including chlorfenapyr, methoxyfenozide, spinosad, and tebufenozide, than to a recommended insecticide, thiodicarb. In other laboratory bioassays, fall armyworms were fed field grown cotton leaves, white flowers, or bolls treated with one of two recommended insecticides, L-cyhalothrin or thiodicarb, or one of four experimental insecticides, chlorfenapyr, emamectin benzoate, methoxyfenozide, or spinosad. First instar mortality was significantly greater on leaves treated with chlorfenapyr, L-cyhalothrin, or thiodicarb than for the untreated control at 24 h after infestation (HAI). First instar mortality was significantly greater on leaves treated with all insecticides, with the exception of methoxyfenozide, than for the untreated control at 48 HAI. Likewise, first instar mortality was significantly greater on white flowers treated with all insecticides, with the exception of methoxyfenozide, than for the untreated control at 24 HAI. First instar mortality on white flowers treated with all insecticides was significantly greater than the untreated control at 48 HAI. Fifth instar mortality on bolls was not significantly different among treatments at 1 day after infestation (DAI). At 3 and 5 DAI, fifth instar mortality was significantly greater on bolls treated with all insecticides, with the exception of methoxyfenozide and spinosad, than for the untreated control. At 7 DAI, fifth instar mortality was significantly greater on bolls treated with all insecticides, with the exception of spinosad, than for the untreated control. These data indicate that these recommended and experimental insecticides are effective in controlling early fall armyworm instars on cotton if larvae come in contact with these insecticides. /// La eficacia de insecticidas convencionales y experimentales contra el gusano cogollero del maíz, Spodoptera frugiperda (J. E. Smith), se evaluó con bioensayos de laboratorio. En un experimento de dieta, se documentó que instares terceros de una colonia de laboratorio eran más susceptibles a los insecticidas nuevos, incluyendo a chlorfenapyr, methoxyfenozide, spinosad, y tebufenozide, que a un insecticida recomendado, thiodicarb. En otros experimentos de laboratorio, los gusanos cogol