Evaluation of chemical composition of Mesosphaerum suaveolen as a potential insecticide for Anopheles gambiae

Abstract

Introduction: Mesosphaerum suaveolens (Lamiaceae), commonly found in tropical regions, is traditionally used for its medicinal and insect-repelling properties. Increase in resistance of Anopheles gambiae to synthetic insecticides coupled with growing concern of mammals’ health and the environment has pose a great need for safer insecticide(s). Thus, the aim of this study was to evaluate the chemical composition of M. suaveolens as a potential natural alternative for mosquito control. Methodology: Aerial parts of the plant were collected, shade-dried, pulverized, and extracted using n-hexane in a Soxhlet extractor. This was followed by the preliminary phytochemical screening, and GC-MS analysis of the crude extract at the Multipurpose Lab, ABU Zaria, Nigeria. Insecticidal efficacy of GC-MS identified compounds was evaluated using the CDC bottle bioassay on adult A. gambiae at concentrations of 2000, 4000, and 6000 µg/bottle. Findings: The preliminary qualitative phytochemical analysis revealed the presence of high concentration of terpenoids, with minute concentrations of alkaloids, tannins, saponins, and glycosides. From GC-MS analysis, eight potential insecticidal compounds were identified, including caryophyllene, caryophyllene oxide, phytol, and spathulenol. Results of insecticidal efficacy showed a dose-dependent increase in mortality: 44%, 83%, and 100% respectively within 24 hours. Probit regression gave LC₅₀ = 666.59 µg/bottle and LC₉₅ = 1,571.95 µg/ bottle. Although ANOVA showed no statistically significant differences among treatment groups (P = 0.125), the consistent mortality trend confirms the biological relevance of the extract. Conclusion: This study highlights M. suaveolens as a promising candidate for developing plant based, eco-friendly insecticides in mosquito vector control programs.