Evaluation of the insecticidal effects of <i>Hyptis suaveolens</i> (L.) for the management of <i>Callosobruchus maculatus</i> (F.) on two varieties of cowpea, <i>Vigna unguiculata</i> walp

Abstract

Studies were conducted at the laboratory of the department of Crop, Soil and Pest Management, the Federal University of Technology Akure, Ondo State, Nigeria to test the insecticidal effects of powder from the leaf of Hyptis suaveolens (L.) for the management of Callosobruchus maculatus (F.) on Oloyin and Ife brown varieties of cowpea, Vigna unguiculata Walp. Five levels of the powder,0.00, 0.05g, 0.1g, 0.2g and 0.3g per 20g of cowpea varieties were evaluated against Callosoruchus maculatus under laboratory conditions of 25-28 o C, 65-75% RH). Mortality of C. maculatus was assessed at 24hours, 48hours and 72hours after treatment application. Data were taken on oviposition, seeds with and without eggs, seeds with and without holes, adult emergence, seed weight loss and germination tests. The results from the study revealed that the percentage mortality increased significantly with concentrations. Highest number of C. maculatus died in seeds treated with 0.3g of the powder. Reduced values were obtained on treated seeds compared to the untreated and were significantly different at p<0.05. Treated seeds had fewer eggs laid, reduced emerged adults and seeds with eggs. Similar result was also observed for seeds with and without holes. Untreated seeds germinated better than the treated seeds and showed statistical differences. Significantly higher weight loss was recorded in the untreated seeds compared with the seeds treated with 0.3g of hyptis powder. The results obtained in this study showed that the tested powder exerts protectant effects on the cowpea seeds and that the powder of Hyptis suaveolens is a potential bioinsecticide in the management C. maculatus. Therefore it is recommended that higher rates of the powder and other components such as oil, water extract and ash of the plant should be investigated.