Influence of selected legume seeds on emergence of Callosobruchus maculatus (F.) and its susceptability to Azadirachta indica (A. Juss) aqueous leaf extracts

In the absence of effective protection, grains of legumes may be completely decimated when attacked in storage by the cowpea bruchid, Callosobruchus maculatus. The use of botanical insecticides has been reported as ecologically innocuous alternatives to conventional insecticides for the control of C. maculatus in stored legume grains. This study thus investigated how legume type influenced the emergence of C. maculatus and its susceptibility to the aqeous extract of neem leaf (a botanical based insecticide). Thirty (30) C. maculatus adults from the same population were reared for 4 generations on improved varieties of cowpea (IT89KD391), mung bean (NM 92) and soybean (TGX 1448) seeds under laboratory conditions. While both cowpea and mung bean supported the emergence of adult C. maculatus in all the four filial generations studied, emergence in soybean terminated after first filial generation. Susceptibility of fourth filial generation adult beetles from cowpea and mung bean to neem leaves aqueous extracts was subsequently tested by contact application. Treated adult C. maculatus of the mung bean line were found to be significantly (P<0.05) more susceptible to the botanical extract than those of the cowpea line. It was thus concluded that cowpea and mung bean seeds are more suitable for the emergence of adult C. maculatus than soybean seeds and that its management in storage with neem leaves aqueous extract should be done bearing in mind that the type of legume being treated might influence the effectiveness of the botanical insecticide.