Larvicidal and adulticidal effects of Ethiopian medicinal plants against Anopheles gambiae (Diptera: Culicidae).

Background: The malaria control programmes are facing a challenge due to a rapidly increasing resistance to currently available synthetic insecticides. Medicinal plants offer a promising alternative for mosquito control, addressing environmental and resistance concerns. The study aimed to assess the larvicidal and adulticidal effects of crude extracts and fractions of selected Ethiopian medicinal plants.

Methods: Methanol crude extract/fractions of leaves of Croton macrostachyus (Euphorbiaceae) and Dodonaea angustifolia (Sapindaceae), rhizomes of Kniphofia foliosa (Asphodelaceae) and roots of Rumex abyssinicus (Polygonaceae) were tested for their larvicidal and adulticidal activity against late 3rd to early 4th instar larvae and 3 to 5 days adults of Anopheles gambiae, respectively. For both assays, the plants were incubated with the parasites for 48 h at concentrations of 25, 50, 100, 200, and 400 ppm. Percent mean mortality rate was compared using one-way ANOVA, and LC₅₀ and LC₉₀ values were calculated using a generalized linear Probit model.

Results: Croton macrostachyus crude extract exhibited the strongest activity, achieving 100% mortality rate at 400 ppm, with LC₅₀ (69.43 ppm) and LC₉₀ (219.39 ppm) for larvae and LC₅₀ (55.32 ppm) and LC₉₀ (86.77 ppm) for adults. The ethyl acetate fraction of C. macrostachyus was particularly effective, with an LC₅₀ of 38.60 ppm for larvae and 52.72 ppm for adults, superseding all other extracts and fractions. Kniphofia foliosa was the next most potent, though it required slightly higher concentrations.

Conclusions: The crude extract and ethyl acetate fractions of C. macrostachyus as well as the rhizome of K. foliosa showed a promising biopesticide activity that could further be developed for malaria vector control.