We tested the effectiveness of volatile oils of Lippia adoensis Hoschst, Cymbopogon citratus (DC) Stapf., Eugenia uniflora L., Lantana camara L., and Chromolaena odorata (L.) King and Robinson at a dose range of 5 to 50 p.1 in protecting 9.9 g (50 seeds) of stored cow pea from infestation by the cowpea weevil, Callosobruchus maculatus F. The effectiveness of the oils as fumigants ranked as follows: L. adoensis > C. citratus > E. uniflora. Oils of L. camara and C. odorata were unsuitable for fumigation purposes. At doses of 5 to 20 μl, oil of L. adoensis protected cowpea from weevil attack. At 5 μl, volatile oil of L. adoensis was as effective as 20 μ1 each of E, uniflora and C. odorata, and only slightly inferior to C. citratus. Insecticidal activity of L. adoensis against C. maculatus was unequalled by any other oils tested. The effective doses of these oils did not impair the viability of treated cowpea.

The efficacy of the powder and volatile oil of Piper guineense Schum & Thonn at protecting cowpea against seed beetle, Callosobruchus maculatus (F.) was tested in the laboratory. At low concentrations the powder significantly reduced oviposition and adult emergence while oviposition was completely suppressed at a higher concentration of 42%. The same concentration provided adequate protection for the same amount of cowpea placed in containers of different volumes. The powder, however, did not show any fumigant effect. Volatile oil at 0.002 and 0.005% significantly reduced oviposition and adult emergence, while oviposition was completely suppressed at 0.02% and above. Weight loss of seeds at 90 days after treatment with volatile oil decreased as concentration of the oil increased. The practical significance of the results in small scale storage of cowpea is discussed.