Phylogenetic community structure and stable isotope analysis of the parasitoid community associated with Eastern spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae)

Eastern spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), is a major pest of eastern North American forests. Outbreaks of spruce budworm occur every 30-40 years, causing high tree mortality. Researchers have established that higher proportions of hardwood trees within stands (higher hardwood content) may reduce the defoliation and mortality of balsam fir and spruces during spruce budworm outbreaks. One mechanism posited to explain these patterns is that hardwood trees positively impact the parasitoids of spruce budworm. Indeed, parasitism of spruce budworm by parasitoids has been found to be impacted by hardwood content. However, more research is needed to understand how hardwood content impacts the parasitoid community as a whole. In this study, we trialled the use of two analyses, phylogenetic community structure and stable isotope analysis, to examine how hardwood content influenced the parasitoid community associated with spruce budworm. We found that phylogenetic community structure differed between forest stands with different hardwood content. Furthermore, the trophic relationships between several parasitoids and caterpillars on balsam fir or hardwood trees changed within and between years. Our study highlights the potential of these two analyses for understanding how hardwood content influences the parasitoid community associated with spruce budworm.