Effects of initial infestation levels on damage to resistant and susceptible cowpea byCallosobruchus maculatus(Fabr.)

Cowpea cultivars Ife Brown and IT84S-2246-4 were screened for resistance and susceptibility to Callosobruchus maculatus (Fabr.) infestation using different insect densities. The number of eggs laid on the seeds; number of seed bearing eggs and seed without eggs; mean number of eggs per seed; number of F1 progeny; number of seed with and without holes; mean number of seed with hole; and developmental time increased as insect population increased. Significantly, more eggs were laid on the seed of Ife Brown (Susceptible cowpea variety) than on IT84S-2246-4. However, low adult emergence and high development period were observed on IT84S-2246-4, indicating clear cultivar difference at all insect population. The assessment of the first filial generation (F1 progeny) of the two varieties showed further that oviposition reduced in the insect that emerged from IT84S-2246-4 (resistant variety) when reared on Ife Brown cowpea seeds. Irrespective of cowpea varieties used in the experiment, egg laid and adult emergence by C. maculatus significantly increased with an increase in insect density.