Monitoring the susceptibility to insecticides in Helicoverpa armigera (Lepidoptera: Noctuidae) populations in Brazil

Helicoverpa armigera was officially detected in Brazil in 2013. This pest has been more difficult to control with some conventional insecticides in comparison with other lepidopteran pests attacking Brazilian agriculture. Understanding the current susceptibility of H. armigera populations to insecticides is crucial to implement Insect Resistance Management Program in Brazil. In this study we characterized the concentration-response lines for some insecticides such as indoxacarb, deltamethrin, thiodicarb, chlorpyrifos and chlorfenapyr. Topical bioassay method was used to deltamethrin, thiodicard and chlorpyrifos; and diet-overly bioassay to indoxacarb and chlorfenapyr, using third instar larvae. The LC₅₀ ranged from 0.19 to 0.57 µg a.i./cm² for indoxacarb, 0.29 to 0.69 µg a.i./cm² for chlorfenapyr, 0.21 to 0.55 µg a.i./larvae for chlorpyrifos, 0.88 to 4.87 µg a.i./larvae to thiodicarb and pyrethroids presented a LC₅₀ higher than 10 µg a.i./larvae. Diagnostic concentrations (LC₉₉) were defined for monitoring H. armigera susceptibility to insecticides.