Validation of a Spruce Budworm Phenology Model Across Environmental and Genetic Gradients

This report presents the results of an ongoing investigation into the variability of spruce budworm (Choristoneura fumiferana (Clemens)) development rates over its geographic distribution. The first phase of the study involved rearing laboratory colonies from the Insect Production Services (IPS) in Sault Ste. Marie at seven constant temperatures (i.e. 5-35ºC), which allowed us to develop and test rearing protocols. It also provided an opportunity to assess the accuracy of BIOSIM’s Spruce Budworm Biology Model predictions for the phenology of laboratory colonies that have been kept in isolation from wild populations for many generations. Our results indicate that the model fits the phenology of the laboratory colonies very well over the 15-25ºC range. For lower and higher temperatures (5-10ºC and 30-35ºC, respectively), the model tends to overestimate development rates. In 2017, we successfully completed the second phase of the project, which involved establishing colonies from wild budworm populations sampled in five locations across its geographic distribution, from Inuvik to northern Quebec. A trend analysis of simulated budworm phenology at these five locations for the period 1998-2017 reveals a trend towards a faster overall larval development (L2-L6) that is statistically significant for Inuvik (NT) and almost significant for High Level (AB). The samples collected in these locations were reared through to the next generation to provide enough individuals in each colony to run seven temperature experiments. Preliminary results for the Ontario colony reared at 30ºC and 35ºC are similar to what was observed with the IPS colonies, i.e. the current phenology model tends to overestimate the development rate at these temperatures. Other temperature treatments for Ontario and Quebec are ongoing while the other colonies have not yet completed their obligatory diapause.