VARIETAL SUSCEPTIBILITY OF COWPEA (VIGNA UNGUICULATA L.) TO THE STORAGE BEETLE, CALLOSOBRUCHUS MACULATUS F. (COLEOPTERA: BRUCHIDAE)

Abstract

Twenty-two cowpea genotypes, comprising eighteen elite lines from the CSIR-Savanna Agricultural Research Institute, and three improved cultivars from the International Institute of Tropical Agriculture were evaluated for their susceptibility to infestation and damage by the storage beetle, Callosobruchus maculatus F. The assessment of their relative susceptibilities was based on oviposition, mean developmental period, adult emergence, seed weight loss and growth index. The results showed that the number of eggs laid on the seeds was significantly different among the genotypes. More eggs were laid on seeds of SARC 3-122-2, Marfo-Tuya and SARC 1-119-2, while SARC 1-132-1, SARC 1-91-1 and SARC1-13-2 recorded the least egg load. The mean development period was also significantly higher on SARC 3-122-2, SARC 4-75 and Marfo-Tuya (21.1-21.5 days), and lower on SARC 1-57-2, SARC 1-136-2 and Apabgaala (18.4-18.9 days). A significantly higher number of adults emerged from SARC 1-34-2, SARC 1-136-2 and Apabgaala, while SARC 1-132-1, SARC 3-103-1 and SARC 1-119-2 recorded the least. Moreover, Apabgaala, SARC 1-36-1 and Marfo-Tuya recorded the highest percentage weight loss (24.0-29.4%) while SARC 1-132-1, SARC 3-90-2 and SARC 3-103-1 recorded the least (4.3-9.6%). Overall, SARC 1132-1, SARC 3-90-2, SARC 1-91-1, SARC 1-13-2 and SARC 3-103-1 consistently demonstrated high tolerance to to infestation by C. maculatus and therefore, should be promoted or incorporated into further breeding programmes to help minimize the high grain losses incurred by farmers during storage.