In 1958, the World Health Organization intensified the efforts to eradicate malaria. The insecticide DDT was found to kill the malaria-causing mosquitoes and the incidence of malaria fell dramatically. After only five years of spraying, the momentum reversed. Every two years the number of people suffering from malaria doubled. The mosquitoes had developed a resistance to DDT. The startling realization of how quickly and effectively mosquitoes develop resistance to chemical control was to be seen again and again in the attempts to control insects - both those carrying disease and those plaguing farmers' crops. The malaria story - an intensive pesticide campaign followed by new generations of pests who outlive any attempt to kill them - by now is a familiar one. It has happened in efforts to wipe out insects that carry diseases, and it has happened when farmers have tried to rid their fields of pests.
This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities.
Agenda 21 recommends carrying out national reviews, as appropriate, of previously accepted pesticides whose acceptance was based on criteria now recognized as insufficient or outdated and of their possible replacement with other pest control methods, particularly in the case of pesticides that are toxic, persistent and/or bio-accumulative.