Laboratory Evaluation of the Toxic and Repellent Effects of Three Edible Oils on Cowpea Bruchid, Callosobruchus maculatus (F.) [Coleoptera: Bruchidae].

Abstract

Toxicity and repellency of the oil extracted from benniseed (Sesamum indicum L.), olive (Olea europaea L.), and horseradish (Moringa oleifera Lam.) were evaluated in the laboratory on cowpea bruchid, Callosobruehus maeulatus (F.), at 28- 31°C and 41-72% RH. The tests were laid in completely randomized design with four replications per treatment. The rates of oil tested for toxicity were 0 (control), 0.10,0.20,0.30,0.40 and 0.50 g/10 g cowpea seeds. The repellency test was conducted in Petri dish containing treated and untreated Whatman No.1 filter paper; the rates of oil tested were 0 (control), 0.5, 1.0, 1.5 and 2.0 g/30 cm”. LC50 was calculated from probit analysis of toxicity data while repellency data were analyzed with GENSAT 2005 programme. The oil from each of benniseed, olive, and horseradish caused significantly higher (P<0.05) mortality to C maculatus adults at 24 h post-treatment compared to the control treatment; the olive oil was the most potent ( LC50 of 0.125 g/10 g seed) and benniseed oil the least potent (LC50 of 0.279 g/ 10 g seed). At the highest rate of application, the three oils evoked Class V repellency (81.0% for horseradish; 81.0% for olive, and 91.8% for benniseed). The toxicity and repellent effects of the oils imply that stored cowpea seeds can be adequately protected against C. maculatus.