Insects, one of the major groups of Arthropoda, possess modular body plans and discrete postembryonic developmental modes, namely ecdysis.  Many of social insect species show multiple phenotypes with diverse body plans even within a single colony.  The caste system is a representative example of polyphenism, in which various phenotypes are produced depending upon environmental stimuli.  During the postembryonic development, the body plan of an individual is determined to fit to a task, to which the caste is allocated.  Here I present some of our accumulated data on the developmental regulations of caste differentiation in some termite species, and discuss them in terms of evolutionary developmental biology, i.e. Evo-Devo.
    So far, we have been mainly focusing on the soldier differentiation in the damp-wood termite Hodotermopsis sjostedti.  We investigated the developmental processes of soldier morphogenesis and analyzed the accompanying gene expression profiles.  Moreover, as endocrinological factors play significant roles in controlling caste development, we applied juvenile hormone analogue to induce soldier differentiation.  Caste differentiation does not only require changes in external morphologies but also those in internal organs like digestive or nervous system.  However, the developmental responses against hormonal signals differ among individual body parts.  For example, when we applied a juvenile hormone analogue, pyriproxyfen, to nymphs of Zootermopsis nevadensis that were in the course of alate development, it was shown that there should be some trade-offs between alate and soldier characters.  In other words, the responsiveness against the JH signal is very different between alate- and soldier-specific characters.
    In addition, the comparison of alate formation among species suggested that there have been heterochronic shifts of caste-specific organ development that is thought to be in deep relation to ecological factors like the reproductive strategies.  All things considered, I will discuss the evolution of developmental regulation in termite caste differentiation.