WOLBACHIA AS A POSSIBLE MEANS OF DRIVING GENES INTO POPULATIONS

Cytoplasmic incompatibility consists of sterility in cross matings, th e crossing type being maternally inherited. It can be explained by the action of Wolbachia symbionts which are transmitted through the egg c ytoplasm and leave an imprint on the sperm which prevents it fertilizi ng unless it is 'rescued' by the action of the same type of Wolbachia in the egg. Thus matings between infected males and uninfected females are sterile, but the reciprocal matings are fertile. Hence uninfected females are at risk of failing to transmit their uninfected cytoplasm if they cross mate, but infected females are at no such risk. Therefo re natural selection favours the infected state and in two wild insect populations the infection has been observed spreading. If a gene for inability to transmit malaria could be introduced into Wolbachia and i f this could be introduced into Anopheles (where these symbionts appea r not to occur naturally), release of a limited number of such insects should trigger a process of displacement of malaria vectors, by the n on-vector type. A simple model is used to demonstrate the limitations to this process which would be introduced by immigration.