Baseline Susceptibility of Helicoverpa punctigera (Lepidoptera: Noctuidae) to Indoxacarb, Emamectin Benzoate, and Chlorantraniliprole

Abstract

Susceptibility in Helicoverpa punctigera (Wallengren) to emamectin benzoate, chlorantraniliprole, and indoxacarb was established from feeding assays on insecticide-incorporated artificial diet in the laboratory. The variation in dose responses was examined in H. punctigera field populations collected in eastern Australia between September 2013 and January 2016 and compared with a laboratory strain. Chlorantraniliprole was the most toxic insecticide with an average LC50 of 3.7 µg of insecticide per liter of diet (n = 12 field strains). The average LC50 for emamectin benzoate was 5.6 µg of insecticide per liter of diet (n = 11 field strains), whereas indoxacarb had the lowest toxicity with an average LC50 of 172 µg of insecticide per liter of diet (n = 14 field strains). Variation in susceptibility between field strains was low at 1.9-, 2.4-, and 2-fold for chlorantraniliprole, emamectin benzoate, and indoxacarb, respectively. Narrow ranges of intra-specific tolerance, high slopes, and goodness-of-fit to a probit binomial model suggested feeding bioassays using insecticide-incorporated diet were a more effective laboratory method for measuring dose responses of these insecticides in H. punctigera than traditional topical bioassays. We propose discriminating concentrations of 0.032, 0.026, and 4 µg of insecticide/ml of diet for chlorantraniliprole, emamectin benzoate, and indoxacarb, respectively, to monitor insecticide resistance in H. punctigera. Although the potential for H. punctigera to develop insecticide resistance is considered low based on historical records, recent changes in population dynamics of this species in eastern Australia may have increased the risk of resistance development.

Keywords: insecticide; management; monitoring; resistance.