Effect of grain splitting on biology and development of Callosobruchus Maculatus (Coleoptera: Bruchidae) in storage

Abstract

Bruchids belonging to Callosobruchus spp. Order Coleoptera are the main storage loss causative pests on cowpea grains in East Africa. Losses have been estimated to be as high as 5-15 % within a few months of storage at farmers’ level. In this study the effect of grain splitting on the biology of C. maculatus was investigated. The cowpea grain treatments compared included split grains + no testa, split grains with testa, compared with whole un-split cowpea grains. Gravid female 4-day old C. maculatus were allowed to oviposit on the cowpea grain which had been pre-conditioned to 12% moisture content, then removed. Data on oviposition, adult eclosion and weights of emergent adults were collected over 3 weevil development generations. Mean separations were done using Analysis of Variance. There was significant reduction (P< 0.05) in oviposition and emergent adults for C. maculatus at F1, F2 and F3 generations on spilt compared to whole grains. Mean oviposition levels on split grain without testa was with only 1.3 ± 1 eggs compared to 258 ± 14 eggs in the controls at F3. Oviposition levels reduced with generation time in all the treatments. The control had the highest adult weevil emergence and mean adult weevil weights (78.8 ± 6.9) with no emergent adults from completely split grains at F3. Mean weevils were highest in the controls and reduced with generation time with least adult weights from the split grain. In this study we conclude that grain splitting reduces development of C. maculatus spp. and could be a viable option in the integrated management of this bruchid pest during storage at farmer level.