Investigation of insecticidal activities of essential oil extracted from some selected plants against maize and bean weevils

Abstract

Maize and beans are the worldwide basic staple foods especially in the developing countries but unquantifiable amount is lost through insect pest infestations. Sitophilus zeamais Motschulsky and bean weevils are among the dominant pest of maize grains beans in tropics. They usually infest maize and beans either just prior to harvest or during storage in traditional structures such as granaries, nylon bags, gourds, storage rooms in a house and warehouse. Adult weevils perforate the grains as they feed and females lay hundreds of eggs inside which continue to destroy the kernel as they develop. This result into loss of agronomic, nutritional and commercial value of the grains causing high level of food insecurities and stunted economic growth leading a vicious cycle of poverty. Currently, the control of Bean weevils and Sitophilus zeamais predominantly depend on the use of synthetic insecticides. However, the use of synthetic insecticides has implications with regard to human health and environmental risks, problem of pest resistance and resurgence of insect infestation. Therefore, new and efficient substance with low environmental impact are needed to control insect pests during grain storage. The objective of this research is to establish the insecticidal activity of selected local plants (such asgarlic and lemongrass) to extract their essential oil, determine repellency effect and contact toxicity which are, safer and environmentally-friendly insecticides. In the study, plant materials will be collected, extracted, steam distilled and applied on insects. This research study aimed at extracting essential oil from garlic bulbs and lemongrass, and determination of the repellency and toxicity effect rate against maize and bean weevils when essential oil is used as an insecticide. Garlic and lemongrass essential oil was extracted by hydro distillation using distillation apparatus for 14 hours and yield was 8ml each. Garlic and lemongrass essential oil contained active ingredients which show repellency and toxicity effect against of maize and bean weevils. The repellency and contact toxicity was determined by using a total of 100 maize weevils and 100 bean weevils in five different concentrations of 72.7%, 66.6%, 57.1%, 40% and 0.00%, first dilution yielded 70%, second concentration yielded 50%, third dilution yielded 40%, fourth dilution yielded 20%, and zero dilution yielded 0.00%s , Generally, from the above results, bean weevils are said to be more susceptible to garlic EO and lemongrass compared to the maize weevils, this is because the bean weevils had a high repellency and mortality rates as compared to maize weevils as subjected to both oils at the same time. It has also been noted from the above that the repellent effects of garlic and lemongrass oils are more effective compared to the contact toxicity since at 57.1%v/v concentration, gave 100% of the insects had been repelled away as soon as the oil was administered and 90% of the insects were dead after 25minutes when garlic and lemongrass oil was sprayed over their bodies. More research to be done on the toxicity of prolonged use of organic insecticide on human. There is need also to elucidate the precise mechanisms by which they exert their insecticidal effect