Azinphosmethyl-resistant first instarEpiphyas postvittanafrom Mariri, Nelson, New Zealand possessed a similar level of resistance to another methyl organophosphate phosmet, but only low resistance to the ethyl organophosphates chlorpyrifos and triazophos, and to a methyl carbamate, carbaryl, by a direct spray technique. There was no evidence of resistance to pyrethroids. Concentration-mortality responses of larvae from azinphos-methyl resistant or susceptible strains were established after 3 weeks exposure to artificial diet containing azinphos-methyl, chlorpyrifos, or carbaryl. The resistance factor of a mildly azinphos-methyl resistant strain was increased significantly following one generation of selection with the LC99of azinphos-methyl. Selection of the same mildly resistant strain with chlorpyrifos raised the level of chlorpyrifos tolerance, but did not affect the response to azinphos-methyl compared to the unselected parent strain. Similarly, selection with the LC99of carbaryl did not affect azinphos-methyl resistance, although resistance to carbaryl was increased 6-fold in two generations (compared to tiie maximum recorded of 25-fold in a reference resistant strain). Resistance was also investigated in field-collected strains. Sixteen lines of progeny were established from field collection of single females. Offspring from each female were split into two groups and exposed to diagnostic concentrations of azinphos-methyl or carbaryl. Progeny of survivors of azinphos-methyl were exposed to diagnostic concentrations of chlorpyrifos. The distribution of carbaryl resistance and chlorpyrifos tolerance was consistent with the distribution of azinphos-methyl resistance, suggesting a common detoxication mechanism or close genetic linkage. Field application of carbaryl would therefore not be expected to provide control of azinphos-methyl-resistantE. postvittana.