The incidence of malaria in many African countries south of the Sahara is falling rapidly, shows new research. Scientists have discovered that the mosquito carrying the malaria parasite has practically disappeared from villages without organized mosquito control, and they do not know why. Since the researchers can discount mosquito nets, the question is whether the mosquitoes have succumbed to disease, or communities have been using pesticides, or whether the fall is due to the chaotic new precipitation patterns.