Adjusting the phenology model of codling moth (lepidoptera: tortricidae) in Washington State apple orchards

Studies were conducted with codling moth, Cydia pomonella L., to fit cumulative curves for the occurrence of injured fruits and male moth catches in sex pheromone-baited traps as a function of accumulated degree-days after the start of moth flight. Twelve data sets were collected from seven apple, Malus domestica Bordhausen, orchards in Washington State from 2003 to 2006. Cumulative data were grouped across years for orchards either treated with sex pheromone dispensers or untreated and fit to logistic equations for both the first and second generation. No significant differences were found for the cumulative curves of moth flight or egg hatch between pheromone-treated and untreated orchards; thus, these data were combined. These new logistic models for moth flight and egg hatch were compared with a widely used distributed-delay model originally developed in Michigan. The cumulative flight curves for the logistic and distributed-delay models were statistically different (slopes) for the first but not the second generation. Cumulative egg hatch in the logistic model was significantly different from the distributed-delay model (intercepts and slopes) for both generations. Most strikingly, the timing of 50% egg hatch during the first generation was delayed 100 DD in the logistic model. The potential impact of this change in the characterization of codling moth's phenology on the effectiveness of insecticide programs targeting eggs and newly eclosed larvae was examined. Possible explanations for this significant difference between the models are discussed.