The effect of time of harvest on the damage caused by the cowpea weevil Callosobruchus maculatus (Fab.) (Coleoptera: Bruchidae)

The effect of time of harvest on the level of damage caused by Callosobruchus maculatus on cowpea was studied. Cowpea (Vigna unguiculata) (variety Asontem) was planted on 9 raised beds each measuring 2.4 x 2.4 m, 3 each for early, mid and late harvests that is, 60,70 and 80 days after germination respectively. Each plot had 20 plant stands. The plants were sprayed with PAWA (Lambda cyhalothrin) at 5 weeks after germination and with Cymethoate at flower bud and pod formation stages. Harvesting was done by hand-picking pods from the inner rows of plants. The harvested pods were sun-dried and the seeds were removed and stored in sealed transparent bottles. The number of adult weevils emerging were collected and counted weekly for 8 weeks. Percent weight loss, damaged seeds and seed holes were noted for each harvest time. Mean number of emerged adults ranged from 1.7 for 60 days of harvest to 136.7 for 80 days of harvest. Significantly higher % damage was recorded for the 80 days harvest than the 60 and 70 days harvest (P= 0.0001). Percent weight loss for the different harvest times however did not differ significantly (P=0.571). Prompt harvest of matured cowpea pods would reduce the destruction of stored cowpea by C. maculatus.  Key words: Callosobruchus maculatus, cowpea, damaged seeds, holes, weight loss.