Insecticidal properties of Clausena austroindica leaf essential oil and its major constituent, trans-anethole, against Sitophilus oryzae and Tribolium castaneum

In this study, the chemical profile of the leaf essential oil of hitherto uninvestigated shrub Clausena austroindica B.C.Stone & K.K.N.Nair and its insecticidal potential against two stored product pests, Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) are being investigated. Essential oils from the leaves of C. austroindica collected from two locations in south India were isolated by hydrodistillation and analyzed by gas chromatography-flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS). Six to eight compounds comprising 99.41–99.44% were characterized with trans-anethole (phenyl propanoid) as the major component (95.12–97.44%) in leaf essential oils. Trans-anethole was isolated from the leaf oil by column chromatography, characterized by Fourier Transform Infrared (FT-IR), ultraviolet-visible (UV-Vis), 1H-, 13C- and distortionless enhancement by polarization transfer (DEPT 135) nuclear magnetic resonance (NMR) spectroscopy, and quantified by external standardization. Insecticidal activity of C. austroindica leaf oil and trans-anethole were assessed against the rice weevil (S. oryzae) and red flour beetle (T. castaneum) by contact and fumigant toxicity assays. Mammalian cell toxicity of C. austroindica leaf oil and trans-anethole was also tested against L929 cell lines using (3-(4,5-dimethylthiazol-2-yl)−2,5-diphenyltetrazolium bromide) MTT assay and quantification of reactive oxygen species (ROS). C. austroindica leaf oil and trans-anethole demonstrated superior contact and fumigant toxicities against adult beetles of S. oryzae and T. castaneum. C. austroindica leaf oil and trans-anethole showed potential fumigant toxicity against S. oryzae (lethal concentration 50 (LC50) 38.80 & 76.98 µL/L) and T. castaneum (LC50 35.65 & 29.10 µL/L). Relatively less prominent viz., S. oryzae: LC50 leaf oil 469.70 µL/L, trans-anethole 2543.20 µL/L; T. castaneum: LC50 leaf oil, 1090.70 µL/L, trans-anethole 2050.84 µL/L, but significant contact toxicities were displayed by the leaf oil and trans-anethole against the two stored product pests. Both C. austroindica leaf oil and trans-anethole (< 2.0 µg/mL) have not demonstrated any mammalian cell (L929 cell line) toxicity. Our study demonstrates the potential of C. austroindica leaf essential oil as a new botanical insecticide for controlling stored product pests. Its major component, trans-anethole, also showed prominent insecticidal activity.