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 (LC50 = 2.96 mg/L, 4.79 mg/L, and 7.45 mg/L air, resp.) and were more toxic than camphor (LC50 = 21.64 mg/L air) and borneol (LC50 = 21.67 mg/L air). The crude essential oil also possessed strong fumigant toxicity against S. zeamais adults (LC50 = 10.71 mg/L air).