Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 42 2 2004 04 15 89 96 H. Vatandoost 2015 09 28 An investigation was carried out on permethrin-susceptible and resistant strain of malaria vector, An.stephensi. Efficacy of several pyrethroids such as permetrhrin, deltamethrin, lambdacyhalothrin, cypermethrin and cyfluthrin against this species showed that those with an α-cyano group and dibromo substitutions were more toxic to sensitive strains than the other classes like permethrin. The ranking order of toxicity of pyrethroids was different for resistant strains. Evidence of enhanced mono-oxygenase activity and the synergism shown by piperonyl butoxide suggests that each resistant strain possesses a mono-oxygenasemediated resistance mechanism responsible, at least in part, for pyrethroid resistance. https://acta.tums.ac.ir/index.php/acta/article/view/2697 https://acta.tums.ac.ir/index.php/acta/article/download/2697/2679