Bio-prospecting for phytochemcials for Anopheles Gambiae larval control
Control of disease vectors and pest insects by use of chemical pesticides has generated several problems such as insecticide resistance, environmental pollution, safety risks for humans and domestic animals.The spread in resistance to majority of present synthetic insecticides by several mosquito species, in various geographical areas, calls for multi-pronged vector control programs and the necessity to develop alternative environmentally acceptable and cost-effective compounds. Mosquitoes depend on aquatic habitat for larval development, thus the fundamental means of control lies in eliminating their breeding habitats by drainage (temporary dewatering) or natural control such as removal of aquatic vegetation (protection and food). These approaches rarely achieve complete control and need to be reinforced by other measures such as house screening, insecticide/repellent and larvicide application. Insecticide treatment of larval habitats remains more effective in reducing culicine population than the application of residual insecticides to houses. Plants have provided many useful compounds or templates including drugs, agrochemicals, insecticides and dyes. Thus there is need for research on phytochemistry of plants with potential of inhibiting growth and development of/or larvicidal activity against mosquito larvae. The current research has undertaken bio-prospecting for phytochemicals for Anopheles gambiae larval control. Seventeen (17) plants were assayed against An. gambiae larvae. Bio-assay-guided fractionation was performed on crude extracts of Zanthoxylum gilletti and Pittosporum mannii. A total of thirteen (13) compounds were isolated, four of which were found to exhibit An. gambiae larvicidal activity in the range of 3.31-75.72 g/ml (LD50). Three new oxoaporphine alkaloids were isolated for the first time and identified with other six known compounds by spectroscopic techniques (IR, UV, NMR, MS).