Insecticide resistance remains an important issue in cotton, Gossypium hirsutum (L.) production. Bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.) are annual pests of cotton in the southern United States. Beet armyworm Spodoptera exigua (Hübner), and fall armyworm, Spodoptera frugiperda (J. E. Smith) are occasional cotton pests. Spinosad, indoxacarb, and pyridalyl are novel compounds that have demonstrated efficacy against lepidopteran cotton pests. The objectives were to evaluate bioassay method(s) for indoxacarb and pyridalyl and to generate baseline responses of laboratory colonies of bollworm, tobacco budworm, beet armyworm, and armyworm. The adult vial test (AVT) was used to determine responses of lepidopteran cotton pests to indoxacarb, pyridalyl, and spinosad. The LC50 values of indoxacarb and pyridalyl for these insect species exceeded 100 mg/vial, with two exceptions. Dose-mortality values of indoxacarb and pyridalyl were higher than discriminating concentrations of cypermethrin, methomyl, profenofos, and endosulfan used in the AVT for monitoring susceptibility of tobacco budworm and bollworm. These results indicate that the AVT may not be the most efficient test method for indoxacarb and pyridaly for susceptibility monitoring programs. Indoxacarb and pyridalyl were evaluated with diet overlay bioassays using first instar (2-day old) larvae of each species. The LC90 values of indoxacarb for these insect species ranged from 1.5-45.5 ppm. Dose-mortality values (LC90) of pyridalyl for these insect species ranged from 3.6-24.3 ppm. Results from diet overlay bioassays indicate this is a more efficient test method than the AVT for indoxacarb and pyridalyl.
Species 1: Lepidoptera Noctuidae Helicoverpa zea (Bollworm, Corn earworm)
Species 2: Lepidoptera Noctuidae Heliothis virescens (Tobacco budworm)
Species 3: Lepidoptera Noctuidae Spodoptera exigua (Beet armyworm)
Keywords: Insecticide bioassays
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