Forecasting defoliation by the jack pine budworm

A method for forecasting current-year defoliation by the jack pine budworm, Choristoneura pinus pinus Free. (Lepidoptera: Tortricidae), at the stand level is described. The method is based on empirically derived relationships between defoliation and the densities of jack pine budworm egg masses, overwintering larvae, early-larval feeding stages, and pollen cones (micro-sporangiate strobili) of the host trees. Parameters for the forecast model were developed and tested with independent sets of survey data from Ontario combined with more precisely estimated relationships between jack pine budworm survival and the abundance of pollen cones. The method forecasts defoliation categories of light, moderate, or severe with greater than 75% accuracy, with the highest accuracy associated with the most severe defoliation category. Areas for further improvement in the model are identified and discussed in the context of integrating known population ecology of the jack pine budworm with realistic operational requirements of pest managers.