Toxicity and residual activity of insecticides to Grapholita molesta (Lepidoptera: Tortricidae) in apple orchards: implications for insecticide resistance management.

Abstract

Organophosphate (OP) insecticides have been used to control Grapholita molesta (Busck, 1916) in Brazil since 1990. However, the evolution of pest insecticide resistance and toxicological reassessments has led to the replacement of OPs with other chemical groups. This study evaluated the toxicity of the insecticides abamectin + cyantraniliprole (1.1 + 3.7 g a.i./100 L-1), acetamiprid + etofenproxi (9.1 + 16.5 g a.i./100 L-1), emamectin benzoate (0.5 g a.i./100 L-1), Sophora flavescens (Fabales: Fabaceae) (22.8 g a.i./100 L-1), phosmet (87.5 g a.i./100 L-1), and indoxacarb (11.2 g a.i./100 L-1) to eggs, larvae, and adults of G. molesta. Additionally, the residual activity of these insecticides in apple orchards was assessed, and the diagnostic concentration for resistance monitoring was estimated using LC99 values (Lethal Concentration that causes 99% mortality in a susceptible population). In larval studies, all insecticides resulted in mortality rates of more than 90%. The insecticide acetamiprid + etofenproxi reduced larval hatching by 99%. This insecticide with phosmet and Sophora flavescens caused over 80% adult mortality and had a 14-day residual activity in apple orchards. The estimated LC99 (μg.ml-1) for resistance monitoring were 1.75 (indoxacarb), 6.45 (metaflumizone), 9.10 (acetamiprid + etofenproxi), 9.67 (Sophora flavescens), 36.13 (phosmet), and 45.61 (abamectin + cyantraniliprole). The insecticides evaluated have high toxicity for G. molesta, being new tools for integrated pest management and for insecticide resistance management in apple orchards.