Biographer Hamilton Lytle believes these estimates are unrealistic, even if Carson can be "blamed" for worldwide DDT policies. John Quiggin and Tim Lambert wrote, "the most striking feature of the claim against Carson is the ease with which it can be refuted". DDT was never banned for anti-malarial use, and its ban for agricultural use in the United States in 1972 did not apply outside the U.S. nor to anti-malaria spraying. The international treaty that banned most uses of DDT and other organochlorine pesticidesthe 2001 Stockholm Convention on Persistent Organic Pollutants (which became effective in 2004)included an exemption for the use of DDT for malaria control until affordable substitutes could be found. Mass outdoor spraying of DDT was abandoned in poor countries subject to malaria, such as Sri Lanka, in the 1970s and 1980s; this was not because of government prohibitions but because the DDT had lost its ability to kill the mosquitoes. Because of insects' very short breeding cycle and large number of offspring, the most resistant insects survive and pass on their genetic traits to their offspring, which replace the pesticide-slain insects relatively rapidly. Agricultural spraying of pesticides produces pesticide resistance in seven to ten years.