Studies on essential oils, Part 33: chemical and insecticidal investigations on leaf oil of Coleus amboinicus Lour.

Chemical investigations of the leaf essential oil of Coleus amboinicus by GC and GC–MS techniques indicated the presence of six components, accounting for 97% of the total oil. The major component was thymol (94.3%), followed by carvacrol (1.2%), 1,8‐cineole (0.8%), p ‐cymene (0.3%), spathulenol (0.2%), terpinen‐4‐ol (0.2%) and an unidentified component (1.4%). The oil was insecticidal to white termites ( Odontotermes obesus Rhamb.) with 100% mortality at a dose of 2.5 × 10 −2 mg/cm 3 for 5 h exposure. This oil was also more active than the synthetic insecticides, Thiodan and Primoban‐20, against termites, although it was ineffective against Tribolium castaneum, a stored product pest.