Efficacy of the fractions of Chenopodium ambrosioides Linn (Chenopodiaceae) against Anopheles gambiae Giles and Culex quinquefasciatus Say larvae (Diptera: culicidae)

Botanical insecticides are nowadays highly encouraged in mosquito control programs because of their efficacy, specific target, biodegradability, less toxic for non-target species, and safe for the human users. In this context, five fractions of the leaf methanolic extract of Chenopodium ambrosioides were evaluated for their toxic effect against Anopheles gambiae and Culex quinquefasciatus larvae in the laboratory. The plant crude extract and its fractions were diluted in 1 mL of methanol and concentrations of 125, 250, 500, and 1000 ppm were prepared in 100 mL solution with distilled water in the plastic cups. Bi-one was used at a unique concentration of 1000 ppm as positive control and 1 mL of methanol added to 99 mL of tap water was used as negative control. In each preparation test and control, 25 early fourth instar larvae of each mosquito species were transferred and larval mortality was recorded after 24 hours. The phytochemical screening revealed the presence of phenolic compounds, alkaloids, terpenoids, flavonoids, and tannins in C. ambrosioides methanol extract and its 5 fractions. The plant methanol extract and its fractions caused a significant toxic effect against the 2 mosquito species larvae and fraction 1 was revealed as the most potent against both An. gambiae (CL50 = 66.39 ppm) and Cx. quinquefasciatus (CL50 = 251.41 ppm) larvae. Thus, fraction 1 of C. ambrosioides might be used in small-scale potential mosquito breeding sites to reduce the density of the 2 mosquito species assessed around the buildings. This fraction 1 might be furthermore submitted to chromatography for the isolation of the compounds responsible for the larvicidal efficacy.