Carbamate Insecticides Resistance Monitoring of Adult Male German Cockroaches, Blattella germanica (L.), in Southern Iran

The German cockroach, Blattella germanica L. (Dictyoptera: Blattellidae), has become resistant to many insecticides due to control failures in hospital and student dormitory settings of southern Iran. This study was thus designed to detect and monitor carbamate resistance in two strains of German cockroach using lethal dose bioassay methods. Wild dormitory (D) and hospital (H) strains were collected. Adult males were subjected to the jar exposure procedure. A range of concentrations based on the world health organization (WHO) standard concentration of carbamate insecticides (carbaryl, bendiocarb, propoxur) were used. For each insecticide, four to seven different concentrations leading to >0% and <100% mortality were assayed. Ten insects were placed in each jar and the exposure time of contact was held constant for 30 minutes. Mortality data (as LD50) were assessed using probit analysis. Although both strains showed lethality values above those of the WHO standards, the H strain was more resistant to all of the three carbamate insecticides than the D strain, possibly due to the frequent and excessive dosage of these chemicals used in the hospital environment. The order of resistance for H strain was carbaryl > propoxur > bendiocarb. The ratio of LD50 in H strain to that of D strain for bendiocarb was about twice that of the other two insecticides indicating that German cockroaches were most susceptible to bendiocarb under both environments. It is concluded that excessive reliance on carbaryl in both D and H settings has led to resistance.