Larvicidal activity of Kotschya uguenensis plant powders and methanol extracts against Anopheles gambiae s.s. larvae in the laboratory and in simulated ponds

Polar constituents of Kotschya uguenensis Verdc. (Fabaceae) do not exhibit acute toxicity but cause growth disruption of Anopheles gambiae s.s. Gile (Diptera: Culicidae) larvae with eventual death. Time-course larvicidal effects of powders of root and stem barks and their crude methanol extracts in form of emulsions were compared in the laboratory and in artificial semi-field ponds. Kotschya uguenensis powders of root and stem barks and emulsions of their crude methanol extracts were assayed against A. gambiae s.s according to protocols of WHO 1996 & 2005. All formulations were equally effective under laboratory conditions giving 100% larval mortality within three days at a dose of 50 μg/ml of the extracts or concentrations of powders corresponding to the same level of extractable material. Under semi-field conditions, suspensions of the powder materials appeared to perform better than emulsions of methanol extracts. Time taken to give 80% mortality (LT80) of larvae and pupa at 0.1% w/v was 6.06 days for powders of root bark and 5.60 days for powders of stem bark. The LT80 for the root bark extract at 200 μg/ml was 8.28 days while that for the stem bark methanol extract was 12.47 days. No residual effects of the test materials on the larvae or pupae were evident in semi-field ponds 14 days after the re-introduction of the test materials. Our results suggest that, for the control of anophelines in the field, a weekly application of appropriate amounts of powders of K. uguenensis may be effective.