MODELING POSTDIAPAUSE EGG AND NYMPHAL DEVELOPMENT OF THE WHITE APPLE LEAFHOPPER (HOMOPTERA, CICADELLIDAE)

Constant-temperature development studies were conducted with overwintering postdiapause eggs and first-generation nymphal stages of white apple leafhopper, Typhlocyba pomaria McAtee. Plots of development rates versus temperature were nonlinear over the range of temperatures tested, 13-30-degrees-C. Optimum nymphal development for each stage occurred over a narrow range of temperatures, 26-28-degrees-C. Developmental rates (times) for each life stage were normalized and fit to cumulative curves of development (Weibull and logistic functions) to produce a predictive phenology model. Comparison of these curves with the development of two nymphal cohorts under field temperatures showed that the model was significant. However, the fit of the model to data on cumulative egg hatch from three orchards was poor. Comparison of the model with cumulative counts of first generation nymphal stages sampled weekly or biweekly in several orchards between 1986 and 1989 showed the model was on average 0-4 d late in predicting 1, 50, and 99% completion of each nymphal stage. Yet, the model predicted the occurrence of these three events within 7 d of the observed event in > 90% of the comparisons. Prediction of the timing of peak population density of instars 1-3 (the most susceptible life stages to organophosphate insecticides) was < 3 d when stage-specific survivorship rates of < 70% were included in the model.