Baseline toxicity of emamectin and spinosad to Helicoverpa armigera (Lepidoptera: Noctuidae) for resistance monitoring

Acute toxicity studies of emamectin and spinosad against Helicoverpa armigera revealed that the pest is highly susceptible to both the insecticides. The median lethal dose (LD₅₀) of emamectin is 3.86 × 10⁻³ µg per larva. The median lethal concentrations (LC₅₀) of emamectin and spinosad were found to be 0.09 and 2.94 ppm, respectively. The discriminating doses were fixed based on the LC₉₅ of the susceptible population of H. armigera as 0.80 ppm for emamectin and 10 ppm for spinosad. Resistance was not observed when the discriminating doses of emamectin and spinosad were applied on field-collected populations of H. armigera from two intensive cotton growing areas, Coimbatore and Madurai, India.