Insecticidal Activities of Azadirachta indica A.J (Meliaceae) leaf and Seed on Stored Grain Weevils and Toxicological Studies of Pesticide-protected Stored Grains in Nigeria

Abstract

Introduction: Azadirachta indica has been used in Nigeria for decades in traditional medicine for managing various diseases notably are fever, aches, common cold, as well as  urinary tract infections.

Methods: A. indica  leaves and seeds were prepared after air drying into powder forms(PF), aqueous extract(AE) and ethanol extract(EE). Two kilograms of dried leaves and seeds were each prepared by grinding with electronic blender into fine powder, fresh leaves and seeds were  each macerated in 1000mL of water in a basin while 2000g of the other powdered parts were extracted using cold maceration techniques in 1.5 litres of absolute ethanol and concentrated using rotary evaporator. The grains tested were maize, bean, millet and guinea corn; each bagged in 25Kg storage bags and arranged in randomized block design in the laboratory for 8 weeks. Various preparations of A. indica PF, AE, and EE were used to store the grains for the period. % Mortality of weevils, as well as oviposition deterrence were determined in each bag and for each preparation.

Results: The result showed that AE of leaf and seed exhibited 100% insecticidal and oviposition deterrence on Acanthoscelides obtestus (bean weevil) than maize and guinea corn weevil(Sitophilus spp.). Insecticidal activities increases with increased storage time. These results were comparable to the standard pesticide DD force at p≤0.05 (ANOVA).  Acute toxicity determination showed that  LD₅₀ value were  363.10 mg/Kg and 977.10 mg/Kg for beans and maize respectively.