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TECHNICAL
EYE
the market after one year because it was no longer effective.
The biochemical mechanisms that insects and microbes use to protect themselves against a specific toxic chemical are often effective against a wide range of similarly structured or acting chemicals, Mr. Metcalf explained.
Mr. Metcalf, who has worked for the World Health Organization, rites the example of propoxur, shown to be very effective against ualarial mosquitoes in field tests in Africa. But propoxur couldn’t be jsed against mosquitoes in El Salvador because farmers there were spraying carbaryl - a related insecticide - on their crops and rain was carrying it into ponds and streams, breeding grounds for mosquitoes. Before long, mosquitoes appeared that were resistant to both insecticides.
Using pesticides freely was okay as long as new materials were readily available. However, in the early 1970s, as economic and regulatory constraints on development of new pesticides increased, the number of new chemicals introduced worldwide declines. The cost of developing a new insecticide in 1953 was a little over $1 million. Today, that figure is over $40 million.
Since the world’s first documented case of pesticide resistance
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