Application of Two Ocimum Species Powders in the Control of Red Flour Beetles, Tribolium castaneum Herbst (Coleoptera: Tenebronidae), during Wheat Grain Storage

Abstract

Pest insects on stored goods are a problem everywhere in the world because they lower grain yields and quality. This has the impact of creating a significant danger to global food security, which could negatively affect people's well-being. In the human endeavor to lessen the threat caused by these insects, the use of synthetic chemical insecticides has unfavorable effects. Recently, there has been advancement in the use of botanicals and agricultural wastes in the control of these pests. This research investigated the effects of Ocimum gratissimum (African basil) and O. basilicum (common basil) powders against Tribolium castaneum infesting wheat grains in storage. Powders were tested singly and mixed at doses of 0.2, 0.4, 0.6, 0.8 and 1.0 g per 20 g of wheat grains. The following parameters were determined: adult mortality, adult emergence rates, seed damage %, weight loss %, and beetle perforation index. The data showed that two Ocimum powders were efficacious and their effectiveness increased with increasing the dosage and also the exposure time. The population of adult T. castaneum on treated wheat grains was significantly (p < 0.05) decreased by the two tested Ocimum species powders. After 24 hours of treatment, 1.0 g of O. basilicum powder caused 50% mortality of adult T. castaneum. However, the combination of O. gratissimum and O. basilicum powders caused 40% of beetles' mortality. On the other hand, O. gratissimum powder was the least toxic on adult T. castaneum with 30% only mortality. The lethal doses of both tested powders and their combination required to cause 50% mortality of the T. castaneum population after the first day of exposure were 1.09, 1.44, and 1.45 g, respectively. While, the lethal dose required to cause 90% mortality (LD₉₀) was 4.24, 8.44, and 5.38 g after the first day post exposure. This study demonstrated the toxicity of O. gratissimum and O. basilicum powders on the survival of T. castaneum on wheat grains. The least deadly dose was recorded on O. gratissimum. Therefore, it is recommended that poor resource farmers and food vendors use Ocimum powder as a biocontrol to manage the red-rust flour beetle in stored wheat grains.