Developmental endocrinology of ametabolous insects - how it all started

Research over the past century has established how, on the organismal and molecular levels, ecdysteroid and juvenile hormones control the development of metamorphosing insects, the Pterygota (winged insects). The older insect lineages Archaeognatha (jumping bristletails) and Zygentoma (silverfish and firebrats) that are wingless and have no metamorphosis - called ametabolous - have remained largely neglected. Despite this, they provide an invaluable insight into the ancestral state from which the metamorphic network evolved. Insects, together with Protura, Collembola, and Diplura, compose Hexapoda, which is a terrestrial lineage of Pancrustacea. This review focuses on the recent advances in our understanding of endocrine regulation in an ametabolous insect model, the firebrat Thermobia domestica (Zygentoma), and explores the roots of this in other pancrustaceans.