Tehran University of Medical Sciences Journal of Arthropod-Borne Diseases 2322-1984 6 2 2015 10 14 112 118 EN Mojtaba Limoee Depatment of Public Health, Nosocomial Infections Research Center, Kermanshah University of Medical Sciences, Kermanshah, Iran Behroz Davari Department of Entomology, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran AND Kurdistan University of Medical Sciences and Environment Health research Center, Kurdistan, Iran Seyed Hassan Moosa-Kazemi Department of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 2015 10 14 2015 10 14 Background: The German cockroach, Blattella germanica is a major hygienic pest and mechanical vector for path- ogenic agents in hospitals and residential areas. The development of insecticide resistance is a serious problem in controlling of this pest. Toxicity of four commonly used insecticides (permethrin, cypermethrin, malathion and chlorpyrifos) against two hospital- collected strains of the German cockroach was investigated. Methods: Topical bioassay methods were carried out for detecting insecticide susceptibility of adult male cock- roaches. For each insecticide, four to six concentrations resulting in >0% and <100% mortality were used. Three to six replicates of 10 cockroaches per concentration were conducted. The differences between LD50 (µ g/g) values were considered statistically significant only when the 95% confidence intervals did not overlap Results: Two hospital- collected strains of the German cockroach showed low to moderate levels of resistance to chlorpyrifos, permethrin, malathion and cypermethrin based on resistance ratios compared with susceptible strain. Conclusion: The low level chlorpyrifos resistance suggesting this insecticide may still provide adequate control of these strains. While the obsereved moderate levels of resistance to cypermethrin could imply developing resistance to this compound. https://jad.tums.ac.ir/index.php/jad/article/view/164 https://jad.tums.ac.ir/index.php/jad/article/download/164/148