The spruce budworm from Minnesota and Manitoba to Maine and the Maritimes: Blais and budworm paradigms revisited

We revisit the research legacy of J.R. Blais and re-evaluate his contributions to spruce budworm—forest dynamics in light of a century of research, 1924–2025. We trace the evolution of scientific thought on outbreak ecology and reassess Blais’ foundational insights using contemporary data and methods. Blais’ alignment with a bottom-up, host-driven outbreak paradigm—centered on forest composition and epicentric spread—anticipated many findings now supported by modern research. Re-analysis of Blais’ historical outbreak maps (1802–1940) reveals a longitudinal gradient in outbreak frequency aligned with balsam fir distribution, a pattern only visible with century-scale data. While individual outbreaks emerge fragmented and asynchronous, aggregate patterns exhibit long-term trends of increasing periodicity, intensity, and synchrony—consistent with Blais’ suggestion that cycling behavior has shifted, with greater outbreak extents emerging in the 20th century. A paradigm revolution toward Royama in the 1980s discounted forest structure as a driver, shaping interpretations for decades. Yet tree-ring, defoliation, and population data today converge on four conclusions: outbreak periodicity is weak and complex; synchrony is variable; spatial patterns are non-repeating; and host forest structure strongly influences outbreak dynamics. These revelations—many crystallizing in the last decade—validate Blais’ interpretation and support his argument that promoting forest diversity through silviculture remains the most effective strategy for managing budworm risk.