THE resurgence of malaria in some Asian and African countries has become a matter of concern for governments and doctors, as the disease and the mosquitoes that carry it are increasingly developing resistance to the traditional methods of control. Reports from Brazil and South-East Asia, in particular, show that insecticides like DDT no longer work, and some of the bacteria which mosquitoes inject into the patients' blood have become immune to drugs like chloroquine. So the number of deaths and debilitations caused by malaria has been on the rise in some third world countries.