Insecticidal activities of pyrethroids were evaluated in terms of topical toxicities against a susceptible (S) strain and a Rop-c strain having multiple resistance to organophosphates and carbamates. Against the S strain, pyrethroids showed comparable or higher insecticidal activities than conventionally used malathion, carbaryl or MTMC. Pyrethrins and fenpropathrin were highly effective. LD₅₀ values of tetramethrin, permethrin and fenpropathrin in the Rop-c strain were somewhat higher than those in the S strain, but the insecticidal activities of pyrethrins, allethrin and resmethrin against the Rop-c strain were comparable to those against the S strain. Fenvalerate was 4.3 times more effective to the Rop-c strain than to the S strain.