Tehran University of Medical Sciences Journal of Arthropod-Borne Diseases 2322-1984 11 4 2017 12 30 469 481 EN Fatemeh Nikpour 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, Institute for Environmental Research, Tehran Univer-sity of Medical Sciences, 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, Institute for Environmental Research, Tehran Univer-sity of Medical Sciences, Tehran, Iran Ahmad Raeisi Malaria Control Department, Ministry of Health and Medical Education, Tehran, Iran Mansour Ranjbar Independent Malaria Consultant, Tehran, Iran Ahmad Ali Enayati Department of Medical Entomology and Vector Control, School of Public Health, Mazandaran University of Medical Sciences, Sari, 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, Institute for Environmental Research, Tehran Univer-sity of Medical Sciences, Tehran, Iran Mansoreh Shayeghi Department of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Abdol Rasoul Mojahedi Provincial Health Center, Bandar Abbas University of Medical Sciences, Bandar Abbas, Iran Abolghasem Pourreza Department of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 2017 12 17 2017 12 17 Background: The aim of this study was to evaluate different concentrations of deltamethrin combined with formulated piperonyl butoxide (PBO) synergist on various surfaces against the wild strain of Anopheles stephensi, the main malaria vector in Southern Iran under semi-field condition. Methods: Four concentrations of deltamethrin WG 25% (Tagros) and PBO 800EC-UV (Endura) were prepared and sprayed on the pre-designed surfaces in accordance with WHO alliance line of the IRS Micronair®. The WHO’s rec­ommended bioassay kit and method was used during this study. Results: Comparing the mortality rate of mosquitoes, the results showed a significant difference between months after treatment of IRS (Indoor Residual Spraying) (P< 0.05) but didn’t show any significant differences between days during the first and second months (P> 0.05).Statistical test revealed a significance difference between mortality rate of mosquitoes in exposing to concentrations of 1 and 4 (P< 0.05) which demonstrated effect of synergizing PBO on mortality rate. Conclusion: This research as the first semi-field trial on deltamethrin added to different concentrations of formulated PBO for IRS, indicates that deltamethrin+10X PBO is more effective than other concentrations. Therefore, using syner­gists can be suggested as a new tool for prevention of pyrethriod resistance, although more studies are recommended. https://jad.tums.ac.ir/index.php/jad/article/view/772 https://jad.tums.ac.ir/index.php/jad/article/download/772/360