Field trials with plant products to protect stored cowpea against insect damage

Plant products were evaluated under field conditions for their efficacy as insecticides against the cowpea beetle, Callosobruchus maculatus, on stored cowpea. Seeds, mixed with finely ground clay and three volatile oils were stored in air-tight jerry-cans and canisters. Pods were treated with leaf powders of two plant species and stored in traditional palm-leaf huts. Beetle damage was evaluated before and after storage. The treatments did not prevent damage, but after treatment with oils, fewer beans showed beetle emergence holes; also, the percentage of uninfested beans and the weight of one litre of beans were each higher than for untreated beans. The percentage of germination of stored beans was highest after treatment with Ocimum basilicum oil. Leaf powder of Momordica charantia was effective against weight loss of stored seeds, whereas Ficus exasperata caused a decrease in both the percentage of infested beans and the number of emerged beetles, and more parasitoids emerged than from untreated beans. Laboratory tests on the effect of the oils on the development of the beetle and on bean germination did not reveal effects of the oils. We compare data obtained from the laboratory and with those obtained in the field