Susceptibility of Blatella germanica (Blattaria: Blattidae) to Permethrin in Shahid Beheshti Hospital-Zanjan

Blatella germanica as a significant urban pest, can transmit various diseases and cause allergy. In spite of frequent pyrethroid spraying, contamination to German cockroach continues in Shahid Beheshti hospital and so far no survey has been carried out concerning the cause of persistent contamination to this pest. This study was carried out to assess the susceptibility of German cockroach in shahid Beheshti hospital during 2003-2004. In this quasi-experimental study, B. germanica samples were collected from different wards of Shahid Beheshti hospital and transferred to the laboratory. Both hospital and susceptible strains were divided into treatment and control groups. Adult males were sorted out and bioassayed through surface contact with 15.62, 31.25, 62.5, 125, 250 and 500 mg/m2 of permethrin and the number of knockdown samples was counted at different time intervals in all groups. Each dose of permethrin was tested in three replications of ten and a control replication of ten, surface contact with acetone was also carried out. The data were analyzed through probit test and linear regressions between contact time and percentage of knockdown samples was plotted through which knockdown time for 50% of samples (KT50) was estimated. The survey of 480 cockroaches in two group of 240 (60 control and 180 treated) showed resistance to knockdown effect in contact with permethrin in hospital samples. At contact dose of 15.61 mg/m2, hospital samples were heterogeneous (P=0.0004) and resistant samples were easily recognized from susceptible ones. In this dose, KT50 in hospital samples was 63.6 (95% CI: 60.37-67) minutes and in susceptible strain 22.42 (95% CI: 20.28- 26.65) minutes. Resistance ratio in hospital samples reached 2.83 (95% CI: 2.72-2.96). Regarding the resistance to permethrin, the study of genetic nature of resistance, cross resistance to new pesticides and their bioassay are necessary in control measures.