Species delimitation in insects increasingly relies on genomic data, yet greater molecular resolution does not automatically resolve the distinction between population structure and species boundaries. The central difficulty is inferential: ongoing or historical gene flow, uneven geographic and life-stage sampling, model misspecification, prior choices, and discordance among mitochondrial, nuclear, morphological, ecological, and reproductive evidence can all change the partitions recovered by analytical methods. This critical review evaluates how those sources of uncertainty alter taxonomic interpretation rather than treating delimiter output as a species diagnosis. Evidence from recent insect systems shows that gene flow may coexist with persistent genomic differentiation, that mitochondrial partitions may either exaggerate or obscure lineage boundaries, and that geographic structure or locus number can alter inferred species counts. The review therefore advances a proposed validation architecture in which species hypotheses are stress-tested across sampling, demographic, model, and prior perturbations before taxonomic action. The key distinction is between detecting structured evolutionary lineages and justifying species rank. Robust delimitation should consequently emphasize evidence independence, explicit competing explanations, sensitivity analysis, and transparent retention of uncertainty when data cannot discriminate among introgression, incomplete lineage sorting, population structure, or genuine species divergence.
