Well, widespread spraying with DDT did essentially create a permanent reservoir of DDT-resistant mosquitoes, which also made them resistant to pyrethroids. Bit

Well, widespread spraying with DDT did essentially create a permanent reservoir of DDT-resistant mosquitoes, which also made them resistant to pyrethroids. Bit of a problem. Fun fact - DDT makes spider mites extra fertile. I do agree however that the eradication efforts of both caused significantly more good than harm, no question.