Mosquitocidal activities of octacosane from Moschosma polystachyum Linn (lamiaceae).

The toxicity of the plant Moschosma polystachyum was evaluated against mosquito Culex quinquefasciatus. The crude leaf extract and active compound octacosane showed negligible mortality against early third instar larvae of Culex quinquefasciatus. The 24 h LC(50) value was observed at 153.2+/-1.3 mg/l and 7.2+/-1.7 mg/l for crude leaf extract and active compound octacosane, respectively. The repellent activity of active compound octacosane at 1.0 and 2.5 mg/cm(2) concentration gave 85.2+/-1.7 min and 54.6+/-2.3 min protection, respectively. The total percentage protection of octacosane was 96.2+/-0.9 at 2.5 mg/cm(2) and 86.4+/-1.3 at 1.0 mg/cm(2) concentration.