Larvicidal Efficacy of Azadirachta indica, Ocimum gratissimum and Cymbopogon citratus Ethanolic Extracts against Culex quinquefasciatus Larvae

Abstract

Background: Effective and repeated control use of synthetic insecticides has led to the development of resistance development in mosquitoes. This problem has resulted in the need for the development of new strategies for selective mosquito larval control. The present work investigated the larvicidal efficacy of Azadirachta indica, Ocimum gratissimum, and Cymbopogon citratus ethanolic extracts against Culex quinquefasciatus mosquitoes. Methods: Extracts of A. indica, O. gratissimum, and C. citratus were obtained using 80% ethanol after their leaves had been previously air-dried for about 3-4 weeks. Thereafter, the solvent was evaporated with a rota-ry evaporator to eliminate any solvents still present. Twenty-five samples (in four replicates) of 2nd-3rd in-star larvae of C. quinquefasciatus were exposed to various concentrations (20 mg/L, 40 mg/L, 60 mg/L, 80 mg/L, and 100 mg/L) of each leaf extracts using WHO standard procedures. Data obtained were analyzed using the Statistical Package for Social Sciences (SPSS) for Windows, version 14, and statistical differences among mortalities induced by the different concentrations were obtained using Analysis of Variance (ANOVA) at a 95% confidence level (P= 0.05) with the aid of GraphPad prism 8. Results: There was an increase in the mortality rates of C. quinquefasciatus larvae as the concentration of each of the three leaf extracts increased over 24 hours. Eighty mg/L ethanolic extract of A. indica gave a mortality rate of 96.10% (24±0.1) after 24 hours of exposure, 100 mg/L of the same extract of A. indica gave a mortality rate of 100% (25.0. ±0.0) which is significantly (P < 0.05) higher than 96.1% (24±0.1) and 80.0 % (20.0±0.5) at the same conditions in C. citratus and O. gratissimum respectively. Eighty mg/L and 100 mg/L of ethanolic extract of C. citratus gave 51% (12.5±0.7) and 96.1% (24±0.1) mortality rates after 24 hours. However, ethanolic extract of O. gratissimum resulted in the least 80.0 % (20.0±0.5) motility rate of C. quinquefasciatus larvae with exposure to 100 mg/L concentration after a 24-hour duration of exposure. Conclusion: The study concluded that the ethanolic extract of A. indica was the most active, followed by that of C. citratus and then O. gratissimum. The extracts of A. indica, C. citratus, and O. gratissimum hold great larvicidal potential, and they are important tools that can be integrated into the Culex mosquito vector control programme