Evaluation of mosquito larvicidal activity of Azolla pinnata leaf extracts against the filarial vector Culex quinquefasciatus

Abstract

Vector control is a major challenge now-a-days when they became resistance against commonly available insecticides. As an alternative, preliminary laboratory evaluation of Azolla pinnata crude and chloroform: methanol solvent extract was carried out under laboratory trials for control of Culex quinquefasciatus. Crude and solvent extract (chloroform: methanol) extracts of A. pinnata leaves were examined for the larvicidal activity against all the larval instars (1^st to 4^th) of C. quinquefasciatus. Dose-dependent mortality assays were performed using the extracts. Further, determinations of LC₅₀ and LC₉₅ values were accomplished through log-probit analyses and regression analyses. The larvicidal activity was statistically justified through ANOVA analyses. Effects of the extracts were examined on non-target water fauna. Exposure to A. pinnata crude and chloroform: methanol extract increased the mortality of first to fourth-instar C. quinquefasciatus. All the graded concentrations showed significant (P <0.05) larval mortality and the results of the regression equation revealed that the mortality rates were positively correlated with the concentrations of the extracts (R² close to 1). LC₅₀ values of all instars after 24 h of exposure were between 86.99-294.06 ppm for crude and 48.87-111.44 ppm for chloroform: methanol extract. Chloroform: methanol extract is better than crude because the nature of biological components can be enhanced in presence of solvent and secondly the stronger extraction capacity could have produced a greater number of active constituents. The residual effect is noted even at the end of 72 h. A negligible toxicity to the larvae of Chironomus circumdatus was noticed as non-target organisms.