Evaluation of susceptibility of some elite cowpea cultivars to attack by Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Fifteen elite cowpea cultivars were evaluated for their susceptibility to attack and damage by the most destructive storage pest, Callosobruchus maculatus (F.), based on the number of eggs laid, total developmental time, percentage adult emergence, seed weight loss, and growth index. Significantly, more eggs were laid on the seeds of Bengpla, California and Clemson genotypes than on those of the other cultivars. The mean developmental time (days) of C. maculatus ranged from 21.4 days on California 20 to 25.7 days on Sul 518-2 (Marfo tuya), and was significantly different between the cowpea cultivars. Adult emergence was considerably high on Bengpla, California and Clemson genotypes, but low on IT94K-445-2, Melack, and Sul 518-2. Weight loss ranged from 7 to 35.6 per cent and was significantly different between cultivars. The IT94K-445-2, IT98K-279-3 and Valenga cultivars had the least damage whilst California 11, IT87KD-1951 and Bengpla had the highest loss in seed weight. Overall, the susceptibility indices which ranged from 4.8 to 9.4 indicated that IT94K-445-2, Melack, Sul 518-2 and IT98K-279-3 were the least susceptible, whereas Bengpla, California and Clemson were the most susceptible cultivars. Therefore, it is recommended that IT94K-445-2, Sul 518-2, Melack, and IT98K-279-3 that have some degree of resistance to C. maculatus in this study should either be promoted or incorporated into breeding programmes because this will help to considerably reduce storage losses that farmers incur. Quinze varietes de dolique elite etaient evaluees pour leurs predispositions a l'attaque et au ravage par le ravageur de stockage le plus destructeur, Callosobruchus maculatus (F.) fondees sur les variables suivantes; la quantite d'oeufs pondus, la totalite de temps de croissance, le pourcentage d'emergence en adultes, la perte de poids de graine et l'indice de croissance. Considerablement, plus des oeufs etaient pondus sur les graines de genotypes de Bengpla, de Californie et de Clemson que sur les autres varietes. Le temps (jours) moyen de croissance de C. maculatus variait de 21.4 jours sur Californie 20 a 25.7 jours sur Sul 518-2 (Marfo tuya) et etait considerablement different entre les varietes de dolique. Emergence en adultes etait considerablement elevee sur les genotypes de Bengpla, de Californie et de Clemson et faible sur 1T94K-445-2, Melack et Sul 518- 2. La perte de poids variait entre 7% et 35.6% et etait considerablement differente entre les varietes. 1T94K- 445-2, IT98K-279-3 et Valenga ont subi le moindre ravage alors que Californie 11, IT87KD-1951 et Bengpla avaient les pertes de poids de graine les plus elevees. D'ensemble, les indices de predisposition qui variaient de 4.8 a 9.4 indiquent que 1T94K-445-2, Melack, Sul 518, 1T98K- 279-3 etaient les moindres predisposees alors que Bengpla, Californie et Clemson etaient les varietes les plus predisposees. Il est donc recommande que 1T94K-445- 2, Sul 518-2, Melack et 1T98K-279-3 qui avaient une certaine mesure de resistance a C. maculatus dans l'etude actuelle, devraient etre soit encourages soit incorpores dans les programmes de reproduction puisque cela va aider a reduire considerablement les pertes de stockage que les agriculteurs subissent. Ghana Journal of Agricultural Science Vol. 40 (1) 2007: pp. 73-80