Assessment of Bruchid (Callosobruchus maculatus) Tolerance of Some Elite Cowpea (Vigna unguiculata) Varieties

Abstract: The resistance of cowpea to bruchid infestation has been a major concern to plant breeders as some elite cowpea varieties become susceptible to the polymorphic nature of this storage insect pest. The current status of ten bruchid resistant varieties collected from the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria was evaluated for bruchid tolerance. Each of the varieties was infested with two pairs of bruchids and comparative data was taken for 60 days. Results showed a delay in bruchid emergence with mean development period for successful adult emergence ranging from 32-47 days. Nine of the varieties studied showed percentage seed damage above 80% and percentage pest tolerance below 50%. Susceptibility index indicates that seven of the studied varieties to be moderately resistant and the remaining three to be resistance to the bruchid infestation with TVu 11953 being the most resistant of all with index 1.78. Analysis of seed coat resistance indicated no significant difference in number of eggs laid, mean bruchid development time, percentage bruchid emergence, percentage seed damage and susceptibility index between the smooth and rough seed coats. The study indicates other factors, not seed coat nature to be responsible for bruchid resistance in cowpea.