Bioefficacy of Selected Plant Extracts against Sitophilus zeamais on Post-Harvest Management of Zea mays

Abstract

Maize (Zea mays L.) is the most important cereal crop in Kenya with 90% of the total population relying on it as the main staple food. Post-harvest loss in maize is caused by insect pests such Sitophilus zeamais and Larger grain borer and the can sometimes be up to 90 percent. Synthetic chemicals are used to manage weevil infestation in maize. However, chemical residues have been detected on the stored maize prior to consumption. Additionally, continuous uses of synthetic chemicals have led to development of pest resistance reducing their effectiveness. This study therefore sought to evaluate a possible use of Ocimum kilimandscharicum essential oil to manage Sitophilus zeamais. The study also determined the effect of pretreating baglets with aqueous extracts of A. indica and W. ugandensis to enhance efficacy of O. kilimandscharicum oil. Laboratory experiments were carried out to establish insecticidal property of O. kilimandscharicum oil. Additionally, on farm experiments were carried out to establish the oil’s effectiveness and longevity. Maize grains were treated with O. kilimandscharicum oil in the first experiment and in the second treated maize grains were put in miniature synthetic bags treated with aqueous extracts of A. indica and W. ugandensis and stored in a granary for six months. On-farm experiment revealed that O. kilimandscharicum oil doses were effective against S. zeamais as compared with untreated maize grains. However, 10 ml per 1kg of maize grains was the best dosage. Weight loss in maize grains was proportional to the number of holed grains. Replenishment of the oil after the third month (at 6 ml, 8 ml and 10 ml) reduced significantly (p<0.0001) the number of holed grains as well as weight loss. Pretreatment of baglets containing maize grains with aqueous extracts of A. indica and W. ugandensis significantly improved protection of maize grains treated with O. kilimandscharicum oil. From the results of this study it can be concluded that plant extracts can offer a possible substitute to synthetic chemicals in post-harvest management of S. zeamais in stored maize. Use of essential oil of O. kilimandscharicum for post-harvest protection of maize grains against S. zeamais is therefore recommended.