Esterase activity in homogenates of Helicoverpa armigera (Hubner) (Lepidoptera: noctuidae) exposed to different insecticides and the behavioral effect

Abstract

The toxicity of some insecticides to Helicoverpa armigera was studied through sublethal effects, evaluating the enzymatic activity of esterase and the behavioral response. The commercial formulation of insecticides selected were chlorpyrifos, spinosad, indoxacarb, chlorantraniliprole, lambda-cyhalothrin and Bacillus thuringiensis, corresponding the most used by farmers to control of H. armigera. To determine the esterase activity, the larvae were fed with soybean leaf discs dipped in insecticide solution using the lethal concentration (LC₅₀). For the behavioral response, filter paper were immersed in three concentrations of insecticides (LC₅₀, LC₉₅ and recommend dose.), then the behavior of the larvae observed in Videomex-One. The results for the enzymatic activity showed an increase in the activity of the esterase, with variation along the treatments and the time of exposure of the insects to the insecticides. With exception of spinosad, other insecticides showed an increase in EST-α activity, 6 and 24 hours after contact of caterpillars with insecticide.Different behavioral patterns of walking (walking distance, walking speed and resting time) were observed for H. armigera exposed to different insecticides. H. armigera exposed to chlorpyrifos, lambda-cyhalothrin and B. thuringiensis insecticides show greater esterase activity. Regarding walking behavior, the results confirms enzymatic activity, where H. armigera have behavioral alteration after exposure to insecticide.