Insecticidal activities of constituents of Litsea cubeba fruit extracts effective against the maize weevil (Coleoptera: Curculionidae)

In this study, we investigated the insecticidal activities, including contact toxicity, fumigant toxicity, and repellent activity, of Litsea cubeba fruit extracts against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). The extracts, obtained by liquid–liquid extraction in n-hexane, ethyl acetate, chloroform, and water were analyzed by gas chromatography–mass spectrometry. Among the different extract types, chloroform extracts exhibited the strongest repellent, contact, and fumigant activities against S. zeamais. The main components of the chloroform extracts were identified as laurine (21.15%) and 2,6-diisopropyl aniline (16.14%), followed by chlorobutanol (10.54%), 3-O-methyl-N-acetyl-d-glucosamine (10.03%), and 6-methyl-5-hepten-2-one (8.33%). Among the identified components of the chloroform extracts, chlorobutanol showed the strongest fumigant toxicity (LD(50) = 21.91 mg/liter), contact toxicity (LD(50) = 54.25 µg/adult), and repellent activity against S. zeamais. These results indicate that L. cubeba fruit extracts possess natural insecticide-like activities against S. zeamais.