Host-associated differentiation is frequently interpreted as an early stage of ecological speciation, but the evidential steps between host use, population divergence, reproductive isolation, restricted gene flow, and species-level divergence are not interchangeable. This systematic evidence map organizes recent insect literature according to what each evidence class can actually establish. The mapped studies span phylogenetic, population-genomic, ecological, phenological, behavioral, reproductive, molecular, and comparative approaches. Across systems, host association often covaries with genetic or phenotypic differentiation, yet geography, environmental heterogeneity, lineage history, symbionts, incomplete lineage sorting, admixture, and continuing hybridization can generate competing explanations. Phenological displacement and assortative mating provide stronger evidence when they directly alter reproductive encounter or compatibility, but their magnitude and even direction can remain context dependent. We therefore distinguish observed host association from barriers to reproduction and from subsequent species-level inference. The central contribution is a proposed evidence-stage architecture that preserves concordant, discordant, incomplete, and reversible states rather than treating ecological divergence as an inevitable linear progression toward speciation.
