Detection of malathion and chlorpyrifos resistance mechanism in German cockroaches (Blattella germanica, Insecta: Blattodea: Blattellidae) using piperonyl butoxide and tributyl phosphorotrithioate

Introduction: German cockroach (Blattella germanica, Insecta: Blattodea: Blattellidae) is considered one of the most common household pests which can transfer pathogenic agents and also cause allergic reactions. Frequent and uncontrolled spraying caused resistance in German cockroach to insecticides. In this study we aimed, to determine the malathion and chlorpyrifos resistance mechanism of German cockroaches using piperonyl butoxide (PBO) and S, S, Stributyl phosphorotrithioate (DEF) by surface contact. Methods: Eight wild strains of German cockroach were collected by hand catch and trap, and transferred to the insectarium and reared in special glass breeding containers. The susceptible strain was used to compare the results of wild strains to the mentioned strain.. At first the discriminative doses of malathion and chlorpyrifos were determined. 179.14 mg/m2 and 6.63 mg/m2 at 30 minutes of contact were considered as the discriminative doses of malathion and chlorpyrifos, respectively. Then the susceptibility level and resistance type mechanisms of collected strains to mentioned insecticides using PBO and DEF synergists were studied by surface contact method simultaneously at 1:1, 2:1 and 3:1 ratios of synergists and insecticides, respectively. For data analysis ANOVA method was used. Results: The results showed that all wild strains had a degree of resistance to chlorpyrifos and malathion that showed significant differences compared to susceptible strain (P<0.05). Using the 1:1, 2:1 and 3:1 synergistie in chlorpyrifos insecticide-resistant strains, the mortality rate was increased 5-10%, 5-19.5% and 5-20%, respectively (P<0.05). In malathion insecticideresistant strains, the mortality rate was increased 2.5-80%, 2.5-100% and 2.5-100%, respectively (P<0.05). In addition, significant differences between proportions of ratios of PBO with chlorpyrifos was observed (P<0.05). Conclusion: Possibly other mechanisms such as reduction of cuticle penetration or acetyl cholinesterase enzyme insensitive resistance could be involved.