CROSS-RESISTANCE IN THE LIGHTBROWN APPLE MOTH EPIPHYAS POSTVITTANA (LEPIDOPTERA, TORTRICIDAE)

Azinphosmethyl-resistant first instar Epiphyas postvittana from 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 LC99 of azinphosmethyl. Selection of the same mildly resistant strain with chlorpyrifos raised the level of chlorpyrifos tolerance, but did not affect the response to azinphosmethyl compared to the unselected parent strain. Similarly, selection with the LC99 of carbaryl did not affect azinphos-methyl resistance, although resistance to carbaryl was increased 6-fold in two generations (compared to the 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-resistant E. postvittana.