Tehran University of Medical Sciences Journal of Arthropod-Borne Diseases 2322-1984 13 3 2019 08 03 284 296 Sara Rahimi Department of Medical Entomology and Vector Control, School of Public Health, 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 Environmental Chemical Pollutants and Pesticides, Institute for Environmental Research, 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 Environmental Chemical Pollutants and Pesticides, Institute for Environmental Research, Tehran University of Medical Sciences, Tehran, Iran Ahmad Raeisi National Program Manager for Malaria Control, Center for Communicable Diseases, Ministry of Health and Medical Education, Tehran, Iran Ahmad Ali Hanafi-Bojd Department of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran AND Department of Environmental Chemical Pollutants and Pesticides, Institute for Environmental Re-search, Tehran University of Medical Sciences, Tehran, Iran 2019 09 28 Background: West Nile virus (WNV) can cause a fatal disease in humans and it is mainly transmitted to people through the bites of infected mosquitoes. Vector control using insecticides is a very important goal. Study of Culex pipiens re­sistance towards several insecticides in the city of Tehran, Iran was evaluated. Methods: Adult females reared from field-caught larvae from southern part of Tehran and lab strain reared in the insec­tary of Tehran University of Medical Science were determined for resistant status by exposing to 4% DDT, 0.1% bendi­ocarb, 0.1% propoxur, 1% fenitrothion, 0.05% deltamethrin, 0.75% permethrin, 0.05% lambda-cyhalothrin, 0.5% etofenprox, 5% malathion and 0.15% cyfluthrin papers using the standard WHO susceptibility tests.   Results: Results clearly showed resistance development of Cx. pipiens against tested insecticides. Mortalities of Cx. pipiens were less than 90% with high resistance, low knock down rate and knock down time (50%) observed against insec­ti­cides. DDT and Malathion showed the most and least lethal time (LT50) values for the field strain. The results of the knock­down test showed that DDT and deltamethrin had the most and least knockdown times (50%) for the field strain, re­spec­tively, while DDT and lambda-cyhalothrin had the most and least knockdown times (50%) for the lab strain, respectively. Conclusion: Resistance to mentioned insecticides in Cx. pipiens is widely distributed in southern part of Tehran. Regu­lar implementation of susceptibility test in Cx. pipiens mosquitoes will help local public health authorities to develop new and better control strategies. https://jad.tums.ac.ir/index.php/jad/article/view/1178 https://jad.tums.ac.ir/index.php/jad/article/download/1178/464