Screening for candidate Bacillus Spp. for the control of cultcine larvae

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Mosquito breeding sources in and around U.S.T. campus as well other areas in Kai were identified, in addition, suitable breeding resources were set up around the Department of Biological Sciences. Blackfly breeding sites along tan (10) rivers in two onch- cerciasis-endemic areas, at Kintampo and Dunkwa-On-Offin districts, as veil as two rivers around U.S.T. campus, a non-disease-endemic area, were also identified. These sources were screened regularly for moribund and dead mosquito and blackfly larvae. The insects were processed for the isolation of Bacillus spp. Five Bacilius spp. were isolated trial pathogenicity tests of the isolates were performed on fourth instar larvae of Andes aegypti and culex quinquefasciatus. Only one of the isolates showed significant pathogenicicy towards C, quinquefasciatus larvae. This isolate was selected and its larvicidal activity was evaluated through bioasaays. The isolate was multiplied by allowing it to undergo fermentation in nutrient broth under continuous aeration by shaking using a flask shaker. The rate of increase in viable cells and spores as veil as changes in the 1vels of protein, optical density and pH were determined, at specific time intervals, during the course of fermentation, The activity level of the isolate, in terms of the LC50, was estimated to be 3.95 x 103 cfu/ml against C. quinquefaeciatus. Against A. aegypti however, the activity level was found to be extremely by, with LC50 of 4.30 x 106 cfu/ml. Based on microscopic studies, cultural, physiological or biochemical tests, the isolate was identified as a strain of Bacillus sphaericus that produced rather large parasporal inclusion bodies. When phage—typed, isolate did not pod in the same way as any of the know strains of the bacterium. This strain appeared to be a bacteriohpage group 4 strains.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Philosophy in Microbiology, 1990