A loopful of Bti mantained on Luria-Bertani agar medium was transferred to Bacto-Peptona agar medium. After 3 days at 30oC, the petri-disheswere washed with sterilized water (100ml/petri-dish). The suspension obtained represented the inoculum for the semi-solid rice-based fermentation medium. The growth units were incubated until complete sporulation of Bti. The resulting biomass was dried at 60oC in an oven for 24h, sieved through 60 tyler. The retained powder did not show any larvicidal activity. In parallel, colloidal bentonite was treated with organic macromolecules dissolved in toluene, after sedimentation, the botton phase was dried at 120oC for 4h. This treatment led to a spreading and floating clay which resulted in a good carrier for Bti. Then, the the two powders were mixed in the proportion of 1(Bti):150(clay). The bioassays were performed under laboratory conditions utilizing 2nd instar Culex sp. larvae, with 3 repetitions (20 larvae each) being observed during 96 hours. The data were treated with Abbott method. A complete methodology was developed to get floating units of Bti with 143 mg/m2 of biological activity
