Evaluating the biorational profile of selected insecticides in Spodoptera littoralis: from nutritional disruption and genotoxicity to in silico risk analysis

Abstract

Spodoptera littoralis is a highly destructive pest that threatens various economically important crops. This study evaluated the sublethal effects of five insecticides (Chlorantraniliprole, thiacloprid, emamectin benzoate, indoxacarb, and Bacillus thuringiensis) on the nutritional indices and growth of 3rd and 5th instar larvae using leaf-dip bioassays at LC10 and LC50 concentrations. The food conversion efficiency and larval growth rate were analyzed. The safety of the selected insecticides was determined using genotoxicity assay. In silico analysis; a Computational modeling to predict off-target safety and ecological risk, offers a holistic understanding of both the efficacy and safety profiles of insecticides application. The results revealed significant sub-lethal effects on feeding and growth. B. thuringiensis exhibited the highest feeding deterrence index (FDI) to more than 50% for 5th instar larvae. Conversely, Coragen and Indoxacarb showed moderate FDI effects. Thiacloprid at LC50 caused the greatest reduction in the efficiency of conversion of ingested food (ECI). The relative growth rate variably changed across all treatments, values were negative for most treatments, indicating growth inhibition, with Thiacloprid causing the greatest reduction. Impaired food conversion efficiency was detected across treatments, particularly for Thiacloprid and Coragen. Approximate Digestibility (AD) remained high across treatments, with Coragen (99.393%) and B. thuringiensis (99.276%) showing the highest AD values. The comparative genotoxicity analysis through the comet assay revealed that the maximum DNA damage occurred after feeding on Thiacloprid-treated plant leaves, corresponding to a type II effect (25–45% damage). Meanwhile, the bacterial treatment revealed a type I effect corresponding to 0–25% damage. Toxicity studies were supported by in silico physico-chemical properties and toxicity profile. The immunotoxicity, respiratory, oral and dermal toxicity, potential hepatotoxicity and aquatic toxicity were the primary hazards of emamectin benzoate identified in silico. Conversely, it was anticipated that mutagenicity, skin sensitisation and irritation and inhalation toxicity would be low. The findings emphasise that microbial insecticides such as B. thuringiensis are effective feeding deterrents with moderate sublethal effects on food utilisation, whereas chemical insecticides such as Thiacloprid and Coragen significantly disrupt growth and nutrient assimilation. These results provide critical insights into the use of insecticides in integrated pest management programs for S. littoralis.