Actually, would'nt large-scale spraying have a powerful impact on mosquito habitat?
Only where mosquitoes are still susceptible. What Carson seems to have been warning against really was the unknown impacts of mass pesticide use, DDT being the notable pesticide at the time. She pointed out known impacts such as large scale damage to water life, but also strange cases where certain bugs were more susceptible and died in greater numbers than their prey, meaning that although their prey took a significant hit they ultimately returned in larger numbers. An unknown effect.
Also, as noted above there is the concept of cross resistance. Large scale use of DDT has caused mosquitoes to become resistant to other pesticides too. India has apparently largely abandoned DDT use as malaria vector control because it has ceased to be effective. People try and use Sri Lanka as an example of the DDT 'ban':
For example, in Sri Lanka, the program reduced cases from about 3 million per year before spraying to just 29 in 1964. Thereafter the program was halted to save money, and malaria rebounded to 600,000 cases in 1968 and the first quarter of 1969. The country resumed DDT spraying, but it was largely ineffective because mosquitoes had acquired resistance to the chemical in the interim, presumably because of its continued use in agriculture. The program was forced to switch to malathion, which though more expensive, proved effective.[17]
http://en.wikipedia.org/wiki/DDT (a wiki link, but it has a reference there to a book I have seen referred to before on the Sri Lanka case)
The problem seems to be twofold - one is that DDT is claimed to be a panacea when scientists say that it is not, even its use for indoor spraying is questioned over its effectiveness. Also that Carson is blamed as the originator of the modern enviromentalist movement, and so attacks upon her (and thus DDT 'bans') are often shrill and unscientific (see the claims that she is worse than Hitler).
