MONITORING AND CHARACTERIZATION OF INSECTICIDE RESISTANCE IN CODLING MOTH (LEPIDOPTERA, TORTRICIDAE) IN 4 WESTERN STATES

Variation in response to insecticide in codling moth, Cydia pomonella (L.), was surveyed in California, Oregon, Utah, and Washington. Two techniques (topical application and direct incorporation of insecticide into the trap adhesive) were used to assay male moths caught in pheromone traps. Using the LC75 from a susceptible population as a standard dose, we monitored 20 apple and pear orchards for resistance to azinphosmethyl by the topical application technique. Orchards in California had the greatest interpopulation variability in resistance levels. In a single pear orchard in the Sacramento Delta, the level of resistance at the LC50 was almost-equal-to 6.2 and 7.2 times greater than in a susceptible population when bioassays were done by topical application and adhesives were mixed with insecticide, respectively. Residual bioassays with neonate larvae collected from this site indicated 4.6-fold resistance. Orchards in Oregon showed little variability, and all populations appeared to be susceptible. Populations from Utah orchards showed little variability in the bioassay and were the most susceptible in the four states tested. Populations collected from Washington orchards had the highest tolerance levels. In laboratory tests, female moths were as susceptible as male moths in bioassays with treated adhesive. In similar tests, 5-7-d-old moths were more susceptible than moths 2.5-4.5 and 0-2-d-old, whereas no significant difference was detected between the latter two groups. With the topical adult assay, baseline data were collected for the pyrethroid esfenvalerate from 13 orchards in California, Utah, and Washington. Little variability in susceptibility to esfenvalerate was found among populations within each state.