Insect metamorphosis is often described as a sequence in which changing ecdysteroid and juvenile-hormone titres activate genetically encoded developmental programs. That description is useful but incomplete because endocrine concentration, receptor occupancy, stage identity, chromatin state, and tissue competence are not interchangeable regulatory levels. Recent work instead supports a distributed control problem: steroidogenic tissues integrate nutritional and receptor-tyrosine-kinase inputs; juvenile hormone restrains premature stage transitions through Krüppel-homolog 1-centred regulation; E93 and other transcriptional regulators reshape developmental competence; and individual tissues interpret systemic endocrine signals according to their own temporal and molecular state. This review therefore organizes metamorphic control around a proposed layered-gating model rather than a single endocrine switch. Evidence from Drosophila, Bombyx, Tribolium, Blattella, Manduca, mealybugs, locusts, and Spodoptera is used to distinguish mechanisms strongly supported in particular models from relationships that remain taxon-, stage-, or tissue-dependent. Special emphasis is placed on feedback between ecdysteroid production and neuroendocrine signals, juvenile-hormone–ecdysteroid antagonism, chromatin accessibility, post-transcriptional regulation, and tissue-specific execution. The resulting synthesis argues that developmental timing is best understood as the coincidence of endocrine availability, stage-specifying gene state, and tissue competence. This interpretation does not imply a conserved universal topology; instead, it identifies experimentally separable regulatory layers whose relative weighting varies among insect lineages and developmental contexts.
