Laboratory-based in vivo Exposure of Fall Armyworm (Spodoptera frugiperda) Larvae to Ocimum suave Extracts

Abstract

The Fall Armyworm (Spodoptera frugiperda) threatens cereal production in sub-Saharan Africa, where reliance on synthetic pesticides poses resistance, health, and sustainability risks. This study evaluated insecticidal and antifeedant efficacy of crude Ocimum suave extracts (water, methanol, dichloromethane, hexane) from leaves, stems, and roots against second-instar FAW larvae under laboratory conditions. Larval mortality and antifeedant activity were recorded at 12, 24, and 48 hours post-treatment, with a synthetic pesticide (Karate) as positive control. Data was analyzed by R software (version 4.3.0), normality was checked using the Shapiro-Wilk test. All O. suave extracts showed significant bioactivity versus the negative control. The aqueous extract exhibited the highest overall efficacy, with robust, dose dependent insecticidal and antifeedant effects, likely due to polar compounds such as phenolics and flavonoids. Methanolic and hexane extracts showed considerable but lesser toxicity. As expected, the synthetic pesticide induced the fastest and highest mortality. Findings indicate that polar bioactive compounds in aqueous O. suave extract effectively inhibit feeding and cause larval death. Thus, Ocimum suave especially as a water extract holds significant potential for managing S. frugiperda within integrated pest management. Further research is needed to identify active compounds, develop stable formulations, and validate field efficacy.