Baseline susceptibility of Helicoverpa armigera (Hübner) to emamectin benzoate, chlorantraniliprole, and indoxacarb was determined in feeding assays on insecticide-incorporated artificial diet in the laboratory. The intraspecific variation of H. armigera was established from field populations collected between September 2012 and March 2013, primarily from commercial farms across eastern Australia. Emamectin benzoate had the highest toxicity with a median lethal concentration (LC50) of 0.01 µg/ml diet (n = 20 strains). The LC50 for chlorantraniliprole was 0.03 µg/ml diet (n = 21 strains), while indoxacarb had the lowest relative toxicity with an average LC50 of 0.3 µg/ml diet (n = 22 strains). Variation in susceptibility amongst field strains was 2.3-fold for emamectin benzoate and 2.9-fold for chlorantraniliprole and indoxacarb. Discriminating concentrations of 0.2, 1, and 12 µg of insecticide per milliliter of diet for emamectin benzoate, chlorantraniliprole, and indoxacarb, respectively, were calculated from toxicological data from field H. armigera strains as a first step in resistance management of these classes of insecticide in Australia. The low intraspecific tolerance, high slope values, and goodnessof-fit to a probit binomial model obtained in this study suggest that a feeding assay using diet incorporated insecticide is an effective laboratory method for measuring the dose—responses of these classes of insecticides in H. armigera.
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