EVALUATION OF OVICIDAL AND LARVICIDAL EFFECTS OF LEAF EXTRACTS OF Hyptis suaveolens (L) POIT (LAMIACEAE) AGAINST Anopheles gambiae (DIPTERA: ANOPHELIDAE) COMPLEX

The female Anopheles gambiae s.l is the principalintermediate host/vector of Plasmodium - the causative organism of malaria fever in many tropical countries. After a preliminary acute toxicity screening of leaf extracts of Hyptis suaveolens using descending series of concentrations (1000, 500, 100, 50 and 5 μg/ml ), two extracts (aqueous and ethanolic ) were assayed against freshly laid eggs and larval instars of An. gambiae following the standard World Health Organisation ovicide and insecticide susceptibility bioassay methodology. The results indicate that both ethanolic and aqueous extracts of the test plant significantly (F = 30.23, df = 5, p < 0.01; F = 45.28, df = 5, ρ < 0.01 respectively) reduced the viability of the An. gambiae ova exposed to different doses of the extracts. In the ovicidal assay the lethal inhibition doses of egg hatching (IH50) was 31.52 and 48.01/μg/ml respectively for the ethanolic and aqueous extracts. Also at a dose of 82.5 μg/ml the ethanolic extract completely inhibited An. gambiae hatching whereas the aqueous extract could inhibit only 70.42% egg hatching at the same dose. The results further indicate that both ethanolic and aqueous extracts also exhibited larval median lethal toxic (LC 50 ) values of 62.41 (range 61.22 – 67.04) and 80.02 (range 77.55 – 86.41) respectively thus making both extracts candidates for further fractionation and compound isolation studies to characterize the active phytochemical constituents.