Efficacy of cowdung as a deliberate aquatic pollutanct against Anopheles gambiae

Abstract

The efficacy of cow dung as a deliberate aquatic pollutant against Anopheles gambiae was investigated. Studies were carried out within the laboratories and the insectaries of the School of Biological Sciences, University of Nairobi. Gravid Anopheles gambiae mosquitoes were observed to oviposit eggs of a single gonotrophic cycle in up to three oviposition cups. The proportion of mosquitoes ovipositing in more than one oviposition cup increased as the number of oviposition cups provided was increased (p = 0.003). Also, the mean number of eggs oviposited by individual gravid mosquitoes increased as the number of oviposition cups provided was increased (p < 0.001). The proportion of mosquitoes ovipositing in cow dung polluted water was Significantly influenced by incubation period (p < 0001). None of the mosquitoes oviposited in cow dung incubated for eight or more days. All eggs oviposited in fresh water polluted with cow dung did not develop further. Those that developed (as indicated by changing from white to black) failed to hatch There was no significant difference in the proportion of mosquitoes ovipositing in autoclaved fresh water compared to autoclaved fresh cow dung (p = 0724). Similarly there was no significant difference in the number of eggs oviposited in autoclaved fresh water compared to autoclaved fresh cow dung (0573) However, there was a significant difference in the proportion of mosquitoes ovipositing in fresh water polluted with fresh cow dung compared to autoclaved fresh water polluted with autoclaved fresh cow dung (p < 0001) Similarly there was a significant difference in the number of eggs oviposited in fresh water polluted with fresh \ cow dung compared to autoclaved fresh water polluted with autoclaved fresh cow dung (p < 0001). Early instar larvae died within the first twenty-four hours in fresh water polluted with cow dung However, there was an accelerated rate of development in some late instar larvae which pupated within the first six to eight hours after being placed in fresh water polluted with fresh cow dung. Polluting fresh water with fresh cow dung had no effect on pupae. Although polluting water with cow dung could potentially control Anoplleles qembie«, remedial measures against increased breeding by culicine species need to be employed if this method has to be adopted for malaria control