Choristoneura rosaceana (Lepidoptera: Tortricidae) Resistance to Insecticides in Michigan Apple and Cherry Orchards.

Field populations of Obliquebanded leafroller, Choristoneura rosaceana (Harris), collected from one commercial apple and one commercial cherry orchard in Kent and Newaygo Counties in western Michigan, respectively. A baseline toxicity study of eight insecticides including phosmet, bifenthrin, methomyl, indoxacarb, chlorantraniliprole, spinetoram, emamectin benzoate, and novaluron was conducted on 12- to 24-h-old larvae of the C. rosaceana field populations and compared with a susceptible strain. The resistance levels were low (<10-fold) in all cases except for indoxacarb (>10-fold) in both populations. The cherry population showed levels of resistance to spinetoram, bifenthrin, emamectin benzoate, and indoxacarb with 4.1-, 4.9-, 5.8-, and 21-fold resistance, respectively. The apple population showed levels of resistance to spinetoram, chlorantraniliprole, phosmet, bifenthrin, emamectin benzoate, and indoxacarb with 4.3-, 4.7-, 5-, 5-, 6.3-, and 620.4-fold resistance, respectively. Generally, the apple population showed lower resistance levels to more compounds than the cherry population. Resistance to these insecticides should be monitored periodically for further changes. This represents the first documented case of insecticide resistance for C. rosaceana collected from a cherry orchard in Michigan. A statewide survey of more commercial orchards would help determine the extent of insecticide resistance across Michigan's five tree fruit production regions.