Obliquebanded leafroller (Lepidoptera: Tortricidae) resistance to insecticides: Among-orchard variation and cross-resistance

Data on survival from exposure to azinphosmethyl, cypermethrin, and methomyl within populations from 3 insecticide-free and 9 insecticide-treated orchards from a single geographic area were analyzed to clarify the cause of spatial variation in insecticide resistance in the obliquebanded leafroller, Choristoneura rosaceana (Harris). History of insecticide treatments appeared to explain a significant proportion of the variance in resistance among the treated orchards. The within-population genetic correlations in resistance to the pairs of insecticides suggested the presence of cross-resistance between azinphosmethyl and cypermethrin, 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 obliquebanded leafroller. Pathogens, natural enemies, improved pruning practices, and limited use of insecticides, should be considered to slow the evolution of resistance.