Insecticidal and Repellent Effects of Some Local Plants Against the Rice Weevil (Sitophilus oryzae L.) Infesting Pearl Millet Stored in Northern Benin

The rice weevil, Sitophilus oryzae L. is a widely distributed storage insect pest that causes tremendous damage to stored pearl millet. Farmers employ synthetic chemical insecticides to overcome this constraint, which have significant impacts on human health and the environment. The use of plant extracts and plants can be an alternative to these insecticides. The objective of this study is to evaluate the insecticidal and insect repellent properties of powders and ethanoic extracts of Ocimum gratissimum L., Ocimum basilicium L., Parkia biglobosa (Jacq.) R.Br. ex G.Don., and Azadirachta indica A. Juss. against S.oryzae using antixenosis and antibiosis methods. Deltamethrine insecticide and Bextoxin served as positive controls for antibiosis and antixenosis tests respectively. Untreated pearl millet were used as negative control. According to the results, the leaf powders and ethanolic extract of the four plants had repellent properties and were more repellent than synthetic insecticides. The leaf powder of O. basilicium was more repellent after 1 h (88.24%) and 24 h (80.11%), while that of P. bligobosa was more repellent after 12 h of exposure (78.57%).The P. biglobosa extract exhibited the highest rate of repulsion against S. oryzae at 5% concentration after 2 h of exposure. Deltamethrine had a greater insecticidal effect than powders and resulted in complete mortality (100%) of S. oryzae adults from the first day of treatment. The ethanol extract of O. gratissimum caused the greatest contact toxicity (100% mortality) at 2.5% concentration after 21 days of treatment. Similarly O. gratissimum had a high fumigant toxicity (92.5% mortality) at 7.5 % (160 µL/L of air) of concentration after 24 h after exposure. The results of this study demonstrated that the powders and extracts of the four tested medicinal plants could be utilized as biopesticides, a potential alternative for controlling S. oryzae in stored pearl millet.