Chemical and biological investigation of Plectranthus amboinicus essential oil in the control of Sitophilus oryzae L.

The study investigates the potential of Plectranthus amboinicus essential oil as a natural alternative to synthetic insecticides for controlling the rice weevil (Sitophilus oryzae), a major pest in stored grains. Gas Chromatography-Mass Spectrometry (GC-MS) analysis revealed that the oil contains high concentrations of bioactive compounds such as carvacrol, caryophyllene, γ-terpinene, o-cymene, and caryophyllene oxide, which are likely responsible for its insecticidal effects. The fumigant activity of the oil showed considerable efficacy, with lethal concentration (LC50) values of 48.28 µL L-1 after 24 h and 20.16 µL L-1 after 48 h of exposure, demonstrating its potency in killing S. oryzae. Additionally, contact toxicity tests revealed LC50 values of 6.76 µL/cm2 at 24 h and 3.54 µL/cm2 at 48 h, indicating moderate effectiveness when applied directly. Probit analysis and other statistical methods were employed to determine LC50 values and dose-response relationships. While the results suggest the potential of P. amboinicus oil as a natural pest control agent, further studies are needed to refine its application and evaluate its feasibility within integrated pest management systems.