Bio-insecticide potential of three aromatic plants of Burkina Faso (<I>Ocimum americanum L., Cymbopogon schoenanthus L. and Hyptis suaveolens</I> Poit.) and their importance in cowpea seed conservation

Abstract

Cowpea is an important source of food and income for the populations of sub-Saharan Africa in general and particularly in West Africa. However, farmers face storage and conservation problems. During storage in granaries, cowpea seeds are attacked by insects causing decreased grain weight and quality and sometimes a loss of germination capacity. Traditionally, farmers have used aromatic plants to limit insect damage. The aim of the present study is to test the insecticidal potential of three aromatic plants (Ocimum americanum L., Cymbopogon schoenanthus L. and Hyptis suaveolens Poit.). Cowpea seeds were mixed with increasing amounts of powder from each of the three plants and stored in plastic boxes for 10 month. The results showed that the number of defective seeds varied according to the treatment. O. americanum was the most efficient; the smallest effective dose of powder was 12%. For C. schoenanthus and H. suaveolens, the smallest effective doses were 16% and 18% respectively. With such treatments, no defective seeds and no live or dead weevils were found. Considering all treatments, the cowpea average loss recorded was 6.92 g for O. americanum, 29.46 g for C. schoenanthus and 36.40 g for H. suaveolens. The average loss recorded in the control was 82.23 g. The powders of the three plants had virtually no effect on the seed germination rate after storage. Storage of cowpeas can be considerably improved using all three aromatic species, but O. americanum was the most efficient.
 Keywords: Africa, insect damage, cowpea, storage, aromatic plants, powder.