Ajwain, Trachyspermum ammi (L.) Constituents/Some Derivatives as Stored Grain Protectant against Sitophilus oryzae

Extraction of ajwain seed (Trachyspermum ammi (L.) essential oil, isolation and derivatization of compounds and testing of insecticidal activity against rice weevil are reported. GC-MS analysis of the essential oil showed the presence of mainly monoterpene hydrocarbons (35.91%) and oxygenated monoterpenes (60.57%). Thymol (31.4%) was the major constituent whereas α-pinene (4.44%) and silphine (3.53%) were the minor compounds. The essential oil, its fractions and thymol along with its derivatives (thymyl phenyl ether, thymyl acetate, o-nitro thymol and azo-derivatives) were evaluated against Sitophilus oryzae at four concentrations (1.0–4.0 mg g⁻¹) for their effect on insect mortality and repellency. Thymol was more effective as compared to essential oil or its fractions. Among the thymol derivatives, thymyl phenyl ether was the most effective and showed complete mortality on the 5^th d of exposure. The other derivatives did not show complete mortality even after 7 d of exposure. Based on the results, thymol could be used as a stored grain protectant against S. oryzae.