Resistance of ten elite African yam bean cultivars to the bean weevil Callosobruchus maculatus

The African yam bean Sphenostylis stenocarpa is a nutritious under-exploited legume from Africa, with a potential to contribute greatly towards food security. The seed of this crop is attacked by the bean weevil Callosobruchus maculatus during storage, which can render them unfit for consumption or replanting. Insect-resistant varieties would be ideal and desired as these will require little or no additional costs for insecticides from farmers and will offer immense and long-term health, economic and environmental benefits to the farmers and consumers. In this study, standard procedures were followed to ascertain the resistance of 10 elite S. stenocarpa cultivars to stored product insect pests, C. maculatus and the maize weevil Sitophilus zeamais. Under conditions of natural infestation, seven (7) tropical S. stenocarpa accessions (TSs 9, 10, 33, 60, 93, 126 & 349) were resistant to C. maculatus and had no infestation at all while 3 accessions (TSs 23, 111 & 116) were susceptible.  When the accessions were subjected to intentional infestation with C. maculatus, they showed varying levels of resistance, with TSs 93 as the most resistant accessions and TSs 23 as the least resistant accession. The maize weevil, S. zeamais however failed to establish on S. stenocarpa seeds. While lectin has been implicated in insect resistance by S. stenocarpa, this study found no significant correlation between lectin and the resistance of different accessions. Elite cultivars of the African yam bean S. stenocarpa that are resistant to its major insect pest C. maculatus have been identified in this study. These resistant cultivars will be of significance to future breeding programmes and food security in developing tropical countries and beyond.