Evaluation of the Susceptibility of Elite Cowpea Cultivars to Attack By Callosobruchus Maculatus.

Cowpea (Vigna unguiculata L) Walpers is the most widely adopted grain legume crop in the semi-arid tropics. However, a wide spectrum of insect pests attack the crop  in the field and storage causing severe damage. Among the cowpea pests is the storage beetle, Callosubruchus maculatus (Fabricus) that can render unprotected grain unsuitable for use as food or seed within six months of storage. To reduce both over dependency on chemicals for control and seed loss due to bruchid attack, the search for host plant resistance in cowpea has intensified in recent years. A study was conducted at the Savanna Agricultural Research Institute,, Nyankpala, Ghana in 2007 to evaluate twenty-two cowpea cultivars for susceptibility to damage by C. maculatus. .  The number of eggs laid on the cowpea seeds was significantly different among the cultivars. More eggs were laid on seeds of cultivars SARC 3-122-2, MARFO-TUYA, SARC 1-119-2, SARC4-75 and IT97K-499-35 whereas SARC 1-132-1, SARC 1-91-1, SARC -1-13-2, SARC 3-90-2 and SARC1-57-2 recorded the least. The total development period was also significantly higher on SARC3-122-2, SARC4-75, and MARFO-TUYA, and lowest on SARC1-57-2, SARC1-136-2, SARC1-94A-2 and APAGBAALA. Percentage adult emergence differed among cultivars, ranging from 47.3 to 92.8%. More adults emerged from the seeds of cultivars SARC 1-34-2, SARC1-136-2, SARC1-57-2, APGBAALA and SARC1-36-1 while SARC 1-132-1, SARC3-103-1, SARC1-119-2 and SARC 1-94A-2 recorded the least emerged adults. Cultivars APAGBAALA, SARC1-36-1, SARC1-119-2 and MARFO-TUYA sustained the highest percentage weight loss (24.0-29.4%) while SARC1-132-1, SARC3-90-2, SARC3-103-1 and SARC1-13-2 sustained the least (4.3-9.6%). Cultivars SARC1-132-2, SARC3-90-2, SARC1-91-1 and SARC1-13-2 had susceptibility index (S.I) ranging from 5.3 to 6.3 and were the least preferred by the bruchids (resistant). The resistant cultivars identified in this study could be used as sources of resistance genes for introgression into cowpea breeding populations in West Africa.