Toxicity of insecticides to Chrysodeixis includens and their direct and indirect effects on the predator Blaptostethus pallescens

Abstract

AbstractThe soybean looper Chrysodeixis includens (Lepidoptera: Noctuidae) is a pest of the soya bean, and increasing populations have been observed on several crops in Brazil. Control of this pest is accomplished using insecticides, particularly with new products recently launched in the market. The effectiveness of these insecticides against C. includens and their impact on natural enemies need further study. Therefore, this study aimed to determine the toxicity of nine insecticides for C. includens and their effects on the Blaptostethus pallescens. Toxicity was increased via the addition of an insecticide synergist, and behavioural changes in Blaptostethus pallescens, an anthocorid predator of C. includens, were assessed. Except for acephate, all other insecticides showed high toxicity to C. includens (mortality >80%). The estimated lethal time (LT50) for C. includens was shorter for methomyl, cartap and spinosad than others six insecticides tested in this work. Chlorantraniliprole, chlorfenapyr, deltamethrin, flubendiamide, indoxacarb and spinosad showed selectivity for the predator B. pallescens and exhibited a lower toxicity to the predator than to C. includens. The detoxifying enzymes monooxygenase and glutathione S‐transferase may be involved in the selectivity mechanisms of these insecticides for the predator based on the results obtained with the synergized insecticides. Only the insecticides cartap, indoxacarb and spinosad changed the behaviour of the predator B. pallescens. These three insecticides are repellent, and the predator avoids them. However, the predator tended to remain on the surface treated with flubendiamide longer. Our results suggest that the insecticides chlorfenapyr, chlorantraniliprole, flubendiamide, spinosad and indoxacarb are the most promising compounds for use against C. includens. These compounds also preserve populations of B. pallescens and allow more sustainable integrated pest management programmes.