Molluscicidal and insecticidal properties of sesquiterpene lactones and extracts of Magnolia grandiflora L.

Leaves and the stem bark of Magnolia grandiflora L. were extracted with dichloromethane. Repeated column chromatography followed by crystallization of two extracts led to isolate the two germacronolide sesquiterpene lactones costunolide and parthenolide. Epoxidation of parthenolide with m-chloroperbenzoic acid yielded 1,10-epoxyparthenolide. The structure of the compounds was identified by extensive spectroscopic analysis and compared with those found in the literature. Extracts and sesquiterpenes were evaluated for their molluscicidal and mosquitocidal activities on the freshwater snail, Biomphalaria alexandrina (Ehrenberg) and terrestrial snails, Theba pisana (Muller) and Eobania vermiculata (Muller), and mosquito larvae of Culex pipiens L. Parthenolide revealed the strongest molluscicidal activity among the tested extracts and compounds against the fresh water snail with LC50 value of 14.65 µg ml^-1. This compound also showed the most potent molluscicidal activity against terrestrial snails. It was more toxic than a reference pesticide methomyl to T. pisana after 24 hours of treatment Extracts and sesquiterpenes were less toxic to C. pipiens larvae than the fresh water snail. Costunolide exhibited the highest mosquitocidal activity among the extracts and the isolated compounds with LC50 value of 58.48 µg ml^-1. This is the first report on the molluscicidal and insecticidal activities of extracts and sesquiterpene lactones of M. grandiflora.