Assessment of the insecticidal potentials of the aqueous extracts of some tropical trees as protectant of cowpea seeds from Callosobruchus maculatus infestation

The test plants, Anacardium occidentale, Azardirachta indica, Eucalptus citriodore, Psidium guajava, Gliricidia septum, Dennetia tripetalia and Monodora tenuifolia were extracted with water. The efficacies of the extracts of the test plant as toxicant and grain protectants against Callosobruchus maculatus were investigated using contact toxicity, oviposition and adult emergence as indices. The long-term protectant ability of the aqueous extracts from the test plants on the treated cowpea seeds was also investigated using seed damage, weight loss and seed germination as indices. The results obtained showed that aqueous extracts from Eucalptus citriodora was most toxic to Callosobruchus maculatus, followed by those of Anacardium occidentale, then Monodora tenuifolia and Azardirachta indica. The least toxic extracts on the insects were those of Psidium guajava and Gliricidia sepium. Extracts from Eucalptus citriodora and Anacardium occidentale almost completely prevented infestation and damage of the treated cowpea seeds for a period of three months. Damages of 41.46%, 29.73%, 28.70% and 27.29% were recorded in aqueous extracts from Psidium guajava, Monodora tenuitolie, Gliricidia sepium and Dennetia tripetalia respectively. Mostly all the treated seeds germinated. The results obtained from this study revealed that aqueous extracts from all the test plants were effective in controlling cowpea storage bruchids, Callosobruchus maculatus and could serve as alternatives to synthetic insecticides for protection of stored cowpea seeds against bruchids.