A laboratory assessment of the potential molluscicidal activity of some Nigerian plant species used as anthelmintics

Laboratory studies were conducted to determine the potential molluscicidal activity of five Nigerian plant species used in alternative medicine practice as anthelmintics. Laboratory-bred adult Biomphalaria pfeifferi, the snail host of Schistosoma mansoni in Nigeria, and their viable 0- to 24-hour-old egg masses were separately exposed for 24 hours, in replicated bioassays, to 7.81-4 000 mg l(-1) concentrations of crude ethanolic extracts of the leaves and roots of Annona senegalensis, Anogeissus leiocarpus, Crotalaria retusa, Dalbergia sissoo and Vernonia amygdalina. Fruits and stem bark of D. sissoo were also investigated. The 24-hour LC50 and LC90 values of extracts for target organisms were calculated using probit analysis. Susceptibility of target organisms to extracts varied with the plant species and morphological part. Egg masses and adult snails were most susceptible to D. sissoo fruit extract (LC90 values of 89.29 and 74.33 mg l(-1), respectively) and least susceptible to V. amygdalina leaf extract (LC90 values of 11 864.09 and 6 241.61 mg l(-1), respectively). Concentration-dependent behavioural responses and embryo deaths at the gastrula/exogastrula and/or prehatch snail stages of development were observed in exposed snails and egg masses, respectively. Tested extracts of A. senegalensis, A. leiocarpus, C. retusa and V. amygdalina did not show appreciable toxicities to B. pfeifferi egg masses or adults. For demonstrating significant molluscicidal activity (LC90 < 100 mg l(-1)) and toxicities to egg masses, we recommend further studies on the ethanolic extracts of D. sissoo fruits and roots.