Chaika S.Yu. 2026. The origin of larvae and pupae in holometabolous insects is a possible result of a radical reorganization of their phylotypic stage // Russian Entomol. J. Vol.35. No.3: 279–304 [in English].
Department of Entomology, Faculty of Biology, Lomonosov Moscow State University, Leninskiye Gory, 1, Bld, 12. Moscow 119234 Russia.
Stanislav Chaika: biochaika@mail.ru ORCID https://orcid.org/0000-0002-1298-3724
doi: 10.15298/rusentj.35.3.01
ABSTRACT. This article provides a conceptual review of the phylotypic stage in insects, whose morphological basis is the germ band. The phylotypic stage in insects is currently viewed not only as a repository for the evolutionary conservation of the general body plan and segmentation within large phyla, but also as a trigger for morphological innovation — specifically, the emergence of novel developmental pathways that include larval and pupal stages. In holometabolous insects (Holometabola), unlike ametabolous (Ametabola) and hemimetabolous (Hemimetabola), there is a morphologically distinct and rigidly organized succession of postembryonic stages, because each stage possesses a unique morphology. Holometabolan development operates under a dual morphogenetic program — larval and imaginal — which are temporally and functionally separated. Holometabolan larvae and pupae represent novel morphological forms and developmental stages that emerged during the evolution of insect ontogeny (the primary larva, likely derived from a trochophore-like ancestor, was subsequently embryonized). The most advanced holometabolan clades exhibit a radical reorganization of the germ band, which enables the formation of nearly all segments during the larval phase. This contrasts with insects having intermediate or short germ bands, in which the missing segments are generated in the growth zone via the segmentation clock. The evolution of a novel larval type in Holometabola, characterized by a growth rate that outpaces the development of imaginal systems, is closely linked to the origin of the pupal stage. The pupa represents the peak of morphogenetic activity and does not undergo molting within the stage, except for the final molt to the imago. Owing to these morphological and functional innovations, the Holometabola have reached the pinnacle of biological diversity, surpassing all other taxa in the animal kingdom. This review integrates knowledge from morphology, embryology, genetics, and epigenetics of insect development. Key aspects examined include the molecular genetic regulation of ontogenesis, particularly the control of stage-to-stage transitions, as well as the role of epigenetic mechanisms in shaping phenotypes and promoting the emergence of new phylogenetic lineages.
KEY WORDS: Insecta, Holometabola, phylotypic stage, embryogenesis, larva, pupa, epigenetics, new path of ontogenesis.