Why did DDT stop being used?

Answer 1

"The pesticide DDT was banned in the United States in 1972 because it contributed to the near extinction of birds, including the bald eagle and the peregrine falcon. DDT is a persistent chemical that becomes concentrated in animal tissues, rising in concentration in animals that are higher in the food chain. It is particularly toxic to fish, aquatic invertebrates and insects (including some that are beneficial). While not immediately toxic to birds, DDT causes long-term reproductive problems by causing eggshells to weaken and crack, threatening the survival of many bird species. Because of its chemical nature, once DDT is applied in a field or other environment, it remains in an active form for decades. People throughout the United States still carry DDT and its metabolites in their bodies, 30 years after the pesticide was banned in this country. Most other developed countries have also banned DDT, but it is still used in many developing countries."

Letter to U.S. Agency for International Development (AID) [PDF document] -- April 2004 letter from Environmental Defense to U.S. AID, urging the agency to consider limited indoor use of DDT for malaria control in regions where malaria is spread by indoor-dwelling mosquitoes until better alternatives are developed.