Cross-resistance of the obliquebanded leafroller,Choristoneura rosaceana (Harris), to tebufenozide wasreported from laboratory studies before it had been used in commercialorchards in New York State. Bioassays with obliquebanded leafrollerlarvae from tebufenozide and organophosphate susceptible and resistantcolonies were conducted with chlorfenapyr, emamectin benzoate,fenoxycarb, fipronil, spinosad, and tebufenozide to determine ifcross-resistance was present before these new insecticides wereintroduced into commercial orchards. Resistance ratios ranged from 1.1to 3.2 for all insecticides except tebufenozide (12.8). Significantdifferences between susceptible and resistant colonies were found withemamectin benzoate, fenoxycarb, and fipronil. The effect of themetabolic synergists piperonyl butoxide (PBO) and diethyl maleate (DEM)on tebufenozide toxicity was examined to determine mechanisms forobliquebanded leafroller resistance to tebufenozide and potentialmechanisms for other new insecticides. At a concentration of 20 ppm,PBO and DEM significantly synergized the toxicity of tebufenozide inresistant and susceptible colonies (three- to fourfold). Obliquebandedleafrollers may be resistant to new insecticides with distinct modes ofaction even if these compounds have not been previously used incommercial orchards.