Toxicity of Cypermethrin and Chlorpyrifos Against German Cockroach [ Blattella germanica (Blattaria: Blattellidae)] Strains from Hamadan, Iran.

Abstract

German cockroach has relatively short life cycle and reproduce rapidly. It is the most common medically and public health pest. As a result, it is essential to combat this pest. Cypermethrin and chlorpyrifos are used by private companies in Hamadan to control Blattella germanica. It seems necessary to determine its susceptibility levels to these insecticides. The aim of this study was to determine the susceptibility levels of B. germanica strains to cypermethrin and chlorpyrifos in Hamadan. In this study, the German cockroach strains were collected from two hospitals (Fatemiyeh and Atiyeh) in Hamadan and transfered to the insectarium. The cockroach strains were reared under the same laboratory condition. Then their sensitivity levels were considered to 1, 2, 4, 8 and 16 mg m -2 for cypermethrin and 0.82, 1.65, 3.31, 6.63, 9.945 and 13.26 mg m -2 for chlorpyrifos using surface contact method. Results based on insecticide treated doses, B. germanica strains showed different percent mortality to the insecticides ranged from 13.3-100. The LD 50 and LD 90 and regression lines of the treated insecticides against German cockroach strains indicate that Fatemiyeh Hospital strain is more susceptible to the treated insecticides than Atiyeh Hospital strain. The LD 50 and LD 90 of chlorpyrifos are also lower than cypermethrin, indicated that chlorpyrifos is more effective than cypermethrin against German cockroach. As the slopes of the regression lines are observed mild in this study indicate that the population of the cockroach strains is very heterogeneous. It can be a symbol of insecticides resistance to cypermethrin and chlorpyrifos. As chlorpyrifos and cypermethrin insecticides are also used for residual spraying by private companies and the doses which provide more than 90% mortality are below the WHO recommended insecticide doses. Therefore, chlorpyrifos and cypermethrin insecticides can be used for B. germanica control in Hamadan within regular monitoring and preventive measures of resistance.