Repellency and larvicidal activities of Azadirachta indica seed oil on Anopheles gambiae in Nigeria

Despite the recent decline in the global prevalence of malaria, the disease continues to be one of the major causes of morbidity and mortality among pregnant women and under-five children in Nigeria. The adoption of an integrated approach to malaria control including the use of bio-insecticide will further reduce the burden of malaria. This study determined the repellency and bio-insecticidal effects of Azadirachta indica oil on Anopheles gambiae in Ibadan, Nigeria. The study was experimental in design. Oil was extracted from the ground seed kernel of Azadirachta indica plants using N-hexane as a solvent. Larvicidal tests were carried out on 600 third and fourth instar stages of Anopheles gambiae using an aliquot of extracted oil emulsified with a surfactant (Tween 80) at concentrations ranging from 100 to 500 ppm. Mortality was recorded every 24 h for five days. Repellency tests were carried out by exposing Guinea pigs that were previously treated with the oil mixed with paraffin at 10–40%v/v concentrations, to 70 adult female Anopheles gambiae in netted cages. Data were analysed using descriptive statistics and ANOVA. The oil yield accounted for 40.0% weight of the ground seed kernel. The larvicidal effect was significant across the concentration of the emulsified Azadirachta oil ranging from 91.6-100.0%, compared to the control experiment ranging from 5-15% (LC50 and LC90: -1666.86 ppm and -2880.94 ppm respectively). A 100.0% larval mortality of Anopheles gambiae was recorded within three days at 500 ppm. All the concentrations of the oil solution also caused 100% inhibition of pupae formation. The repellent effect of adult Anopheles was significant (p < 0.05) across the concentrations but with varying degrees of protection. The highest repellent effect was observed at 40.0% (v/v). The possibility of using Azadirachta indica as bio-insecticide against Anopheles gambiae was established in this study.