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Species delimitation requires an assessment of varied traits that can contribute to reproductive isolation, as well as of the permanence of evolutionary differentiation among closely related lineages. Integrative taxonomy, including the combination of genome‐wide molecular data with ecological data, offers an effective approach to this issue. We use genotyping‐by‐sequencing together with a review of ecological divergence to assess the traditionally recognized species status of three closely related members of the spruce budworm species complex, Choristoneura fumiferana (Clemens), C. occidentalis Freeman (=C. freemani Razowski) and C. biennis Freeman, each of which is a major defoliator of conifer forests. We sampled a broad region of overlap between these three taxa in Alberta and British Columbia (Canada) where potential for gene flow provides a strong test of the durability of divergence among …