Insecticidal Activity and Alkaloid Components of Stemona spp. in Thailand

Stemona species have been traditionally used as natural pesticides and medicinal plants. Despite their diversity, the same vernacular name of “Non Tai Yak” has been used for various species in Thailand because of their similar root shapes. However, a variation in phytochemical constituents of different species was observed, leading to their different biological activities. This study determined the insecticidal activities of various species growing in Thailand. The samples representing 7 species and one unidentified species, probably closely related to S. collinsiae, were tested using chronic feeding bioassays with neonate larvae of the polyphagous pest insect Spodoptera littoralis Boisduval (Lepidoptera, Noctuidae). Potent insect toxicity was observed in all S. collinsiae, the unidentified species, and some samples of S. curtisii. S. kerrii as well as S. aphylla and S. ruprestris showed low to moderate activity. S. tuberosa and S. phyllantha showed no marked insecticidal activity. Stemofoline and didehydrostemofoline were found to be the major compounds in the active samples, clearly demonstrating the higher insecticidal effect than the other alkaloids. Thus, stemofoline and didehydrostemofoline sould be used as bioactive chemical markers for the quality assessment of Stemona roots, their extracts and final products for further pharmaceutical and agricultural developments.