Repellent Effects of Ocimum Suave Extracts and Compounds against Prostephanus Truncatus Horn

Abstract

Insect pests cause significant loses to maize grains in storage. Larger grain borer (Prostephanus truncatus Horn) is one of the most important pests of stored maize. Synthetic pesticides are commercially available for managing the pests. However, some of the chemicals have been banned from use because of their adverse effects on environment and living organisms. Therefore, it is necessary the search for alternative control methods that are effective and environmentally friendly. This study determined the repellence activity of extracts and compounds from Ocimum suave for control of P. truncatus. Repellence activity was measured after exposing the insects to test materials for 2, 5, 24, 48 and 96 hours. Chromatographic analysis of extracts from O. suave yielded five compounds and were identified as β-sitosterol, stigmasterol, β-amyrin, lupeol and betulinic acid. The insects were repelled most by the essential oil (mean repellency = 4.61 cm) with repellence distances of 5.83 and 5.38 cm after 2-hours and 5-hours exposure durations respectively. Repellence activity of organic solvents extracts was in the order of n-hexane > ethyl acetate > methanol while that of isolated compounds was in the order of betulinic acid > lupeol > β-amyrin > β-sitosterol > stigmasterol. Findings from this study revealed that extracts of O. suave are effective against P. truncatus which destroy maize and other cereal grains both in the field and in storage.