Stochastic Model of Eastern Spruce Budworm (Lepidoptera: Tortricidae) Phenology on White Spruce and Balsam Fir

Astochastic model of spruce budworm, Choristoneura fumiferana (Clemens), phenology on balsam fir, Abies balsamea (L.) Miller, and white spruce, Picea glauca (Moench) Voss, in northern Ontario was developed based on relationships between the proportion of budworms in each stage (second instar to adult) and accumulated degree-days (DO). Repeated calculations indicated that 8°C was a suitable threshold for degree-day calculations. Fifty percent of the population was in the second instar after 89 and 92 DO above 8°C on balsam fir and white spruce, respectively. Peak occurrence of instars three, four, five, and six, and of pupae, occurred on balsam fir after 108, 154, 204, 295, and 413 DD, respectively; peak occurrence of the same stadia on white spruce occurred after 103, 138, 186, 256, and 370 DD. Fifty percent adult emergence occurred at 467 and 437 DD for balsam fir and white spruce. Tests of the model with independent data showed that it simulated spruce budworm development excellently. Model performance was superior compared with a previously published spruce budworm phenology model.