Fumigant Compounds from the Essential Oil of Chinese Blumea balsamifera Leaves against the Maize Weevil ( Sitophilus zeamais )

Essential oil of Chinese medicinal herb, Blumea balsamifera leaves, was found to possess fumigant toxicity against the maize weevils, Sitophilus zeamais . The main components of the essential oil of B. balsamifera were 1,8‐cineole (20.98%), borneol (11.99%), β ‐caryophyllene (10.38%), camphor (8.06%), 4‐terpineol (6.49%), α ‐terpineol (5.91%), and caryophyllene oxide (5.35%). Bioactivity‐guided chromatographic separation of the essential oil on repeated silica gel columns led to isolate five constituent compounds, namely, 1,8‐cineole, borneol, camphor, α ‐terpineol, and 4‐terpineol. 1,8‐Cineole, 4‐terpineol, and α ‐terpineol showed pronounced fumigant toxicity against S. zeamais adults (LC 50 = 2.96 mg/L, 4.79 mg/L, and 7.45 mg/L air, resp.) and were more toxic than camphor (LC 50 = 21.64 mg/L air) and borneol (LC 50 = 21.67 mg/L air). The crude essential oil also possessed strong fumigant toxicity against S. zeamais adults (LC 50 = 10.71 mg/L air).