Resistance Management A 40-Year Experiment: Codling Moth’s Responses to Guthion and Other Insecticides

The response of adult male codling moth to Guthion was surveyed in 20 orchards using a discriminating concentration (0.3 μg/moth) during 2003. A wide range of responses was found with 17 of the populations being statistically categorized as tolerant to Guthion versus our laboratory population. The post-diapause emergence of six populations was measured and a strong correlation was found between a population’s tolerance to Guthion and a delay in their emergence. Laboratory studies found that these populations did not differ in their rate of larval and pupal development. However, the more tolerant populations also exhibited some reduction in mating success and a strong reduction in fecundity. Bioassays of these populations to fieldcollected residues showed that a 1.0 lb rate of Guthion 50W provided <14 d control and a 2.0 lb rate provided <21 d of control of the most tolerant strains of codling moth. Assail 70WP applied at a 3.4 oz rate provided poor control of Guthion-tolerant populations. Field populations were also tested at two discriminating concentrations selected from studies of the larval responses of our lab population to Guthion, Intrepid, Assail and Success. In these tests, the most tolerant strain to Guthion also exhibited a significantly more tolerant response to Success, Intrepid and Assail.