Insecticide susceptibility and resistance ofBlattella germanica(Blattaria: Blattellidae) in Seoul, Republic of Korea, 2007

Abstract The susceptibility ofBlattella germanica(L.) in the Republic of Korea (ROK) to insecticides was evaluated under laboratory conditions using 12 insecticides currently used by the local public health centers and/or pest control operators in the ROK. The insecticides included seven pyrethroids and five organophosphates. Based on their LD50values, the order of susceptibility ofB. germanicaadults to the insecticides was chlorpyrifos‐methyl, profenofos and chlorpyrifos with values of 0.07, 0.29 and 0.88 µg/♀, respectively. The least susceptibility was obtained with tetramethrin at LD50of 7.39 µg/♀. In the comparative resistance test, the resistance ratios (RR) of 12 insecticides were compared to each other using field‐collectedB. germanicaadults in Seoul between 1993 and 2007.Blattella germanicademonstrated higher RRs to pyrethroids such as λ‐cyhalothrin, and low RRs among the organophosphates. Among the pyrethroids, λ‐cyhalothrin had the highest RRs of 111‐ and 129‐fold differences at LD50and LD90values, respectively. Among the organophosphates, profenofos was observed to have the highest RRs of 4‐ and 15‐fold differences at LD50and LD90values, respectively. However, there were no significant differences in susceptibility to tetramethrin, chlorpyrifos and fenitrothion.Blattella germanicawas more susceptible to pyridafenthion showing a 0.7‐fold difference in a resistance ratio (RRLD50= LD50value of 2007/LD50value of 1993). Resistance ratio of tetramethrin was low, but susceptibility was also not high.