OBLIQUEBANDED LEAFROLLER (LEPIDOPTERA, TORTRICIDAE) RESISTANCE TO INSECTICIDES - AMONG-ORCHARD VARIATION AND CROSS-RESISTANCE

Data on survival from exposure to azinphosmethyl, cypermethrin, and me thomyl within populations from 3 insecticide-free and 9 insecticide-tr eated orchards from a single geographic area were analyzed to clarify the cause of spatial variation in insecticide resistance in the obliqu ebanded leafroller, Choristoneura rosaceana (Harris). History of insec ticide treatments appeared to explain a significant proportion of the variance in resistance among the treated orchards. The within-populati on genetic correlations in resistance to the pairs of insecticides sug gested the presence of cross-resistance between azinphosmethyl and cyp ermethrin, and between azinphosmethyl and methomyl. The positive cross -resistance between insecticides from different classes may limit the potential of rotations to delay resistance development in the obliqueb anded leafroller. Pathogens, natural enemies, improved pruning practic es, and limited use of insecticides, should be considered to slow the evolution of resistance.