Tehran University of Medical Sciences Journal of Arthropod-Borne Diseases 2322-1984 14 2 2020 05 03 1312 1312 Atieh Shemshadian Department of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Mohammad Reza Abai Department of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran AND Department of Chemical Pollutants and Pesticides, Institute for Environmental Research, Tehran University of Medical Sciences, Tehran, Iran Hassan Vatandoost Department of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran AND Department of Chemical Pollutants and Pesticides, Institute for Environmental Research, Tehran University of Medical Sciences, Tehran, Iran Navid Dinparast-Djadid Malaria and Vector Research Group, Biotechnology Research Center (BRC), Pasteur Institute of Iran, Tehran, Iran Mohammad Ali Oshaghi Department of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Abdolrasoul Mojahedi Department of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran AND Provincial Health Center, Bandar Abbas University of Medical Sciences, Bandar Abbas, Iran 2020 06 29 Background: During the past decade, rapid development of insecticide resistance have been reported among many spe­cies of mosquito vectors against four main categories of insecticides worldwide. The aim of the research was to assess the variation trend of susceptibility levels of Culex quinquefasciatus to two insecticides separately for the field popula­tion compared with subsequent generations of the same sample after multiple colonization. Methods: Larvae and pupae of Cx. quinquefasciatus were collected from house sewages and reared to adult which blood-fed on roosters. Ten percent sucrose fed female mosquitoes aged 2–3 days were used for susceptibility tests with DDT and deltamethrin. Susceptibility levels was assessed in the adult stage of field stran Cx. quinquefasciatus against DDT 4.0% and deltamethrin 0.05% and continued up to next six generations undergoing multiple rearing at insectary condition. Results: The susceptibility levels to DDT 4.0% did not change compared to the field with the lab population to six gen­erations. Regarding deltamethrin 0.05%, no significant difference was shown between field strain (58.3%) and 3rd gen­eration (52.7%) compared to the 6th one (33.8%). Conclusion: This finding may reflect the role of the kdr gene in resistance to organochlorine which has cross-re­sistance with pyrethroid insecticides. The results of this study clearly showed the irreversible trend of pyrethroid re­sistance among colonized mosquitoes. This is the first study of the resistance status of Cx. quinquefasciatus in Iran. https://jad.tums.ac.ir/index.php/jad/article/view/1312 https://jad.tums.ac.ir/index.php/jad/article/download/1312/498