Larvicidal efficacy and residual toxicity of plant extracts against Anopheles gambiae s.l. (Diptera: Culicidae) under semi-field conditions in Benatsemay district, southern Ethiopia

Plant-based products can be integrated with the available interventions, that provide better vector control efficiencies. However, since most of the studies were conducted in the laboratory, the effectiveness and duration of the insecticidal properties under field conditions are less understood. This study investigated ethnomedicinal plant extract larvicidal and residual effects against Anopheles gambiae s. l. under semi-field conditions. The ethnomedicinal survey was conducted in the Benatsemay district, South Omo Zone, southern Ethiopia. In this study, leaves of Abutilon bidentatum, Hypoestes forskaolii, and Hchyranthes aspera species were found to have insecticidal effects against mosquitoes in the study district. Consequently, the larvicidal activities of solvent extracts from such plants were tested against susceptible lab colonies and wild larvae. The residual efficacy of the extract was evaluated at a dose of 100.54 ppm for five weeks. Larval mortality was recorded after 24 and 48 h. The highest larvicidal activity was observed in the hexane, acetone, and methanol extracts of A. bidentatum, with each extract causing 100% mortality. Moreover, strong larvicidal activity was observed in the hexane extract of A. bidentatum, with LC₅₀ and LC₉₀ values of 40.77 and 100.54 ppm, respectively. The residual efficacy was extended for three weeks. The results suggest A. bidentatum crude leaf extracts can potentially be used to control of Anopheles gambiae s.l. Further studies are needed to isolate and characterize bioactive compounds and their modes of action.