Chapter 5 - The holometabolan development

Abstract

Holometabolan metamorphosis is characterized by the morphophysiology of the juvenile stages, which is different from that of the adult. It is the developmental mode of the monophyletic superorder Endopterygota. Most holometabolan insects follow the long germ band embryo development, blastokinesis is relatively simple, and there are three embryonic cuticle depositions—EC1, EC2, and EC3—although EC2 may have become very simplified in some groups or even lost in flies. The postembryonic development goes through a number of larval instars, the pupa, and the adult. The larvae do not externally exhibit adult features, like wings, for example. These will be formed in the pupal stage from clusters of imaginal precursor cells, which sometimes adopt a disc-like shape, that lie in the larval epidermis. Larval types are very diverse although they have been classified into four categories: protopod, polypod, oligopod, and apodous. The pupa is generally quiescent and bridges the morphological divergence between the larva and the adult. There are two types of pupa: decticous and adecticous, which can be further categorized into two subtypes: exarate and obtect. In addition to this diversity of larval morphologies in different species, there is the phenomenon of hypermetamorphosis or the occurrence of a diversity of morphologies within the larval period of the same species. Hypermetamorphosis is more frequent among parasitoid species, and two main types can be distinguished: hypermetamorphosis with a wandering first larval instar and with a sedentary first larval instar. Another type of postembryonic development is the contracted life cycle of cavernicolous Coleoptera, characterized by a dramatic reduction in the number of larval instars.