Species identifications have been historically difficult in the economically important spruce budworm (Choristoneura fumiferana) pest complex. Morphological, ecological, behavioural, and genetic characters have been studied to try to understand the taxonomy of this group, but diagnostic character states differ in frequency rather than being complete replacements between each species. I developed a morphology-based character system that focuses on forewing colour components (Chapter 2), as well as eight simple sequence repeats (SSRs, also referred to as microsatellite markers) (Chapter 3). I tested these along with a 470 bp region of COI mitochondrial DNA (mtDNA) (Chapter 2, 4) to determine their congruence with putative species that were identified by adaptive traits (larval host plant, length of larval diapause, larval and adult morphology, pheromone attraction, distribution). The morphometrics system was effective for identification of the five species tested, with only slight overlap between C. fumiferana and C. biennis. MtDNA distinguished C. fumiferana and C. pinus pinus, but the remaining species shared haplotypes. SSRs distinguished four species (C. fumiferana, C. pinus pinus, C. retiniana, C. lambertiana) but the remaining four species that were included in this survey (Chapter 4) remained mixed within two populations. There was evidence for hybridization between several species pairs. I also conducted a detailed study (Chapter 5) in Cypress Hills, an isolated remnant coniferous forest in western Canada, where identifying individuals from the Choristoneura fumiferana complex has been impossible due to the unusual ecogeographic characteristics of the area. I integrated data on behaviour, ecology, morphology, mtDNA, and SSRs, comparing Cypress Hills populations to those from other regions of North America to determine which species they resembled most. I delimited at least three populations, resembling C. fumiferana, C. occidentalis and C. lambertiana. Adult flight phenology, along with pheromone attraction, were identified as major isolating mechanisms between these populations. My studies highlighted the importance of integrative taxonomy for understanding species boundaries. Their patterns of differentiation suggest that spruce budworm species have recently diverged via natural selection in spite of some gene flow. Overall, this work is intended to contribute to more accurate identification of specimens and a better understanding of the evolutionary processes that drive speciation.