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Abstract SUMMARY The possibility of using the bacterial mosquito larvicid Bacillus sphaericus in controling the kpipiens larvae and A. caspius larvae was studied. It is one of the most safe biological agents for human being and animals to decrease the use of chemical insectecides and prevent the environmental polution. The obtained results indicated the following : _ The results indicated that the C. pipiens larvae was more susceptable to the bacterial larvicide Bacillus sphaericus than A. caspius larvae. _ The dosage levels of this bacteria have great influence in its toxicity, high concentrations evoked a rapid lethal response to the entire tested larvae, while low dosage resulted in significant mortality rates with increasing exposure time and water temperature. Biochemical approaches have been developed to increase the activity of Bacillus sphaericus against the Culex larvae and Aedes larvae. These approaches were based on the incorporation of some selected non-toxic chemical compounds with the bacterial Summary ----- -- -- - -- --- --- - - ------ - 51 - larvicide, these compounds may increase the rate of which larvae ingest the particles of bacteria (phagostimulation) therefore high level of larval mortality was obtained. The compounds used was inorganic salts, organic acids and their salts and amino acids, some of these compounds showed a remarkable potentiation to the Bacillus sphaericus activity against the Culex larvae and Aedes larvae. _ It was found that some additives such as sucarose, fractose, glucose, maltose, sorbetol, mannose, molasses, yeast extract, fish meal, larval extract and soyabean powder improve the efficacy of Bacillus sphaericus against the Culex pipiens larvae, that due to their phagostimulation effect. _ Due to the fact that the persistence of Bacillus sphaericus is very short in the field as a result of exposure to ultraviolet radiation various approaches have been adopted in the present study in attempts to increase the persistence of this pathogen to increase its potentiation against the Culex pipiens larvae. _ Laboratory investigations, indicated that the activity of Bacillus Summary ----------- -- - --- - - --- ------ - 52- sphaericus suspension exposed to ultraviolet radiation, can be prolonged after the addition of certain photoprotectants which reduced the effect of U.V-rays on bacterial larvicides. These materials, such as charcoal, chines ink, talc, chalk. The results indicated that charcoal and chines ink had high absorbance values to U.Y-rays, they are also inert, cheap, so they can be used as a good photoprotectant to Bacillus sphaericus from the ultraviolet radiation, and that increase its potentiation against the Culex pipiens larvae. ____ 0 __ |