The misuse of pesticides has inadvertently created strains of monster bugs that can no longer be chemically killed. There are about 30 species that can not be killed by insecticides. These pests have developed enzymes that detoxify a pesticide or slow its penetration.
The number of insect species estimated to have developed resistance to insecticides has risen from 12 in 1946 to 829 in 1980. There was a time when public health specialists thought malaria could be wiped out in some tropical countries. In Sri Lanka, a campaign to kill off mosquitoes with DDT reduced the number of confirmed malaria cases to 10 in 1963. In the late 1960s, the insect "vectors" had developed widespread resistance to the pesticide. By 1970, Sri Lanka was up to 1 million cases of malaria a year.
Malaria had been nearly eliminated from many parts of the world until the World Health Organization decided to eradicate it by using insecticides. WHO spent 21 years and $2 billion before giving up in 1976. The result was a race of malaria-carrying mosquitoes virtually immune to insecticides.