Cypermethrin resistance and reproductive types were examined for T. tabaci strains. Some arrhenotokous and thelytokous strains encoded the sodium channel mutation (T929I) involved in cypermethrin resistance. However, the resistance levels varied to some degree among the strains. A cytochrome P450 inhibitor, piperonyl butoxide, showed different synergistic effects on the strains examined. These results suggest that fundamental and additional levels of cypermethrin resistance in T. tabaci are conferred respectively by reduced sensitivity of the sodium channel and by cytochrome P450-mediated detoxification.