Insecticide resistance and synergism of three fieldcollected strains of the German cockroach Blattella germanica (L.) (Dictyoptera: Blattellidae) from hospitals in Kermanshah, Iran

摘要

The development of insecticide resistance in the German cockroach, Blattellagermanica (L.) is a serious problem in controlling this medically important householdpest. The insecticide resistance status in three hospital-collected strains of the Germancockroach using four commonly used insecticides from different classes (permethrin,cypermethrin, bendiocarb and chlorpyrifos) was detected by topical bioassay methodand preliminary information on possible involvement of monooxygenases in permethrinresistant strains employing synergist piperonyl butoxide (PBO) was obtained. For eachinsecticide, four to six concentrations resulting in 0% and 100% mortality were used.Three to six replicates of 10 cockroaches per concentration were conducted. Forsynergism studies, 100μg PBO per gram body weight of cockroach as the maximumsublethal dose was administered to the first abdominal segment 1 h before insecticidetreatment. The differences between LD50 (μg/g) values were considered statisticallysignificant only when the 95% confidence intervals did not overlap. The resistance ratioand synergism ratio were calculated for each insecticide. All three hospital-collectedstrains of the German cockroach showed different levels of resistance to permethrinand cypermethrin based on resistance ratios compared with SUS strain. Permethrin andcypermethrin resistance ratios ranged from 11.61 to 17.64 and 11.45 to 26.45 at LD50levels, respectively. Low to moderate levels of bendiocarb resistance and low level ofchlorpyrifos resistance were also observed in the hospital-collected strains under study.The synergist piperonyl butoxide (PBO) significantly enhanced the toxicity of permethrinto all strains with different degrees of synergist ratio, 2.45-, 1.87-, 2.51- and 2.38-fold,suggesting monooxygenase involvement in permethrin resistance.