Isolation of insecticidal lectin-enriched extracts from African yam bean (Sphenostylis stenocarpa) and other legume species

Insecticidal lectins were isolated from 20 resistant Vigna and non-Vigna le gumes and tested againstn 3 pests of cowpea namely: Maruca vitrata, Calloso bruchus maculatus and Clavigralla tomentosicollis. Crude lectins were separ ated from seeds using sodium chloride extraction, ammonium sulfate fraction ation, and dialysis. SDS-PAGE indicated the molecular size of ca. 30 kDa fo r the most intense (and presumably active) band. Haemagglutination assays u sing trypsin-treated rabbit erythrocytes suggested that lectins were among the extracted proteins. Extracts from Lablab purpureus and Sphenostylis ste nocarpa both non-Vigna spp., caused greater agglutination than those from t he wild Vigna species. Bioassays on all three insect species using the lect in extracts incorporated in either artificial cowpea seeds (5% w/w) or in m odified Vanderzant legume pod borer diet (1% w/v) indicated that the non-Vi gna extracts were highly toxic to the insects. Mortality after 10 days was > 80% in the most toxic extracts. The extract from one of the accessions of Sphenostylis stenocarpa, an edible legume, was singled out for lectin puri fication and future gene cloning with the view of using it for engineering resistance to cowpea pests.