Larvicidal Activities of Leaf Extracts of Adansonia digitata L. (Malvales: Malvaceae) and Ficus sur Forssk (Rosales: Moraceae) against Culex quinquefasciatus Mosquito (Diptera: Culicidae)

Abstract

Due to the ineffectiveness of synthetic insecticides for sustainable control of Mosquito vectors, whose transmitted diseases are the major causes of morbidity and mortality in the world today, attention has been directed towards insecticide formulations of plant origin. This study was, therefore, carried out to evaluate the larvicidal potential of the methanolic and n-hexane crude extracts of leaves of Adansonia digitata and Ficus sur against fourth larval instar of Culex quinquefasciatus mosquito. The leaves of the plants were collected from Minna, Nigeria, pulverised, extracted and evaporated using Sohxlet apparatus, with methanol and n-hexane as solvents of extraction. The crude extracts of the leaves were screened for phytochemical constituents following standard methods. The larvae were obtained from a Laboratory colony of mosquitoes raised following standard protocols. Test concentrations of 0.0125, 0.025, and 0.05 mg/L of n-hexane and 0.1, 0.25 and 0.5 mg/L of the methanolic extracts were prepared and tested for larvicidal activities against the mosquito following the WHO standard protocols. Larval Mortality was recorded after 24 hours of exposure and mean mortalities computed. Lethal concentration values (LC 50 and LC 90 ) of the extracts were determined using Probit regression analysis. Phytochemical screening revealed the presence of Flavanoids, Tannin, Saponin, Alkaloids, Steroids, Terpenoid, Cardiac glycosides and Anthraquinone, whose presence were solvent- and plant-species-dependent. There were significant differences in the recorded mortality between the various concentrations of each extracts, the solvents types and plant species. The n-hexane extracts of both plants showed significantly higher larvicidal efficacy against the larvae than their methanolic counterpart. While the n-hexane extract of A. digitata was more potent than its F. sur counterpart, the latter’s methanolic extract was more potent than the former. The median (LC 50 ) and upper (LC 90 ) Lethal concentration of methanolic and n-hexane crude extracts of A . digitata leaf were 0.15 and 0.008 mg/L, and 1.21 and 0.22 mg/L, respectively, while these values for methanolic and n-hexane crude extracts of F. sur were 0.13 and 0.015 mg/L, and 2.64 and 0.15 mg/L, respectively. The plants extracts also elicited dose dependent mortality. The findings of this study suggest that A. digitata and F. sur are promising sources of botanical lead agents in the development of sustainable potent larvicides, for integrated control programmes against mosquito-borne diseases.