Optimizing the Use of Essential Oils to Protect Stored Cowpeas from Callosobruchus Maculatus (Coleoptera: Bruchinae) Damage

Abstract

Essential oils extracted from native aromatic plants are currently considered as promising alternatives to protect stored cowpeas from pests inWest Africa. The optimal application of essential oils has not yet been investigated. One key factor to consider would be the practical considerations of cowpea storage, such as quantity of seeds and type of storage container. For this purpose, we tested the efficacy of essential oils extracted from four native plants in controlling Callosobruchus maculatus, the major pest of stored cowpeas. First, we evaluated Callosobruchus maculatus mortality rate in relation with increasing amount of cowpeas. Then, experiments were conducted with essential oil in two different materials: plastic and aluminium in order to determine the weevil perforation index, the intrinsic rate of natural increase and the rate of cowpea germination. In fine, aromatized powder mixed with cowpea seeds are used against Callosobruchus maculatus by evaluating the mortality rate. The quantity of seeds influenced the efficacy of pure Lippia multiflora and Hyptis spicigera essential oils, whereas essential oils from Ocimum americanum and Hyptis suaveolens were not affected by stock size. The type of storage device used influenced the effectiveness of essential oils tested, plastic containers being more suitable than aluminium ones. Ocimum americanum used as contact insecticide in different aromatized powders exhibited variable toxic effects on C. maculatus.We conclude that essential oils appear to be safe alternatives to insecticides for long-duration storage of cowpeas.