Comparative study on the effects of storage period of neem (Azadirachta indica A. Juss) seed oil in controlling Callosobruchus maculatus (F.) infestion of stored cowpea grains

Abstract

The efficacy of the storage period of neem (Azadirachta indica A. Juss.) seed oil (NSO) for the management of Callosobruchus maculatus (F.) infestation of stored cowpea grains was investigated. Fifteen gram cowpea grains of Banjara, a local cowpea cultivar, were treated with NSO stored for 0/freshly prepared, 2, 8, 10 and 15 years, each applied at four dosages (0.00/untreated control, 0.02, 0.04 and 0.08 ml) and in four replicates laid out in a completely randomized block design (CRBD) in the laboratory. One-way analysis of variance (ANOVA) was used to analyze data collected, and significant means at P<0.05 were separated using the least significant difference (LSD). At 0.02 and 0.04 ml dosages, the mean number of C. maculatus eggs laid, severity of grain damage and developmental period of C. maculatus were significantly lower on cowpea grains treated with NSO stored for 2 and 8/10 years, but not amongst NSO storage periods when treated at 0.08 ml. For cowpea grains treated with 0.04 and 0.08 ml dosages, the mean number of emerged C. maculatus adults, percentage grain damage and susceptibility index were not significantly different amongst all NSO storage periods. Also, for each of these parameters, no interaction existed between the storage period of NSO and dosages applied. These results indicate that when applied at moderate to high dosages, NSO, freshly prepared or stored for between 2 and 15 years can effectively manage C. maculatus infestation of cowpea grains.

Key Words: Cowpea grain, Callosobruchus maculatus, neem seed oil, storage period, dosages and Banjara.