The Impact of Six Insecticides on Coccinella septempunctata: A Risk Assessment for Biological Control.

Abstract

Coccinella septempunctata is an important predator of aphids in many cropping systems, but its populations face threats from insecticide applications. This study assessed the selectivity and toxicity of six registered insecticides, spiromesifen, deltamethrin, lambda-cyhalothrin, abamectin, chlorfenapyr, and imidacloprid, to identify options compatible with the conservation of C. septempunctata in bean fields. The insecticides were applied to eggs, third-instar larvae, pupae, and adults, with distilled water serving as the control treatment. Insecticide exposure significantly affected survival, development, and reproductive performance depending on the compound and developmental stage. Spiromesifen was the least toxic, causing minimal effects on egg viability and no significant reductions in adult fecundity when exposure occurred during larval or adult stages. Chlorfenapyr also showed comparatively moderate effects, although some reductions in egg viability and adult reproduction were observed. In contrast, deltamethrin caused extreme toxicity, resulting in complete egg mortality and preventing survival of larval and adult stages. Abamectin, lambda-cyhalothrin, and imidacloprid resulted in major lethal and sublethal effects, including delayed development, fewer adults emerging, and significant reductions in fecundity and egg viability. Exposure during immature stages led to severe carry-over effects that impaired the reproductive capacity of surviving adults. We conclude that spiromesifen and, to a lesser extent, chlorfenapyr appear comparatively safer for C. septempunctata and may be considered for integration into integrated pest management programs aimed at conserving natural enemies. However, further field studies are required to confirm their ecological compatibility under realistic exposure conditions. Future studies should investigate different concentrations and exposure routes.