Endocrine activity during caste differentiation in Zootermopsis angusticollis Hagen (Isoptera): a morphometric and autoradiographic study

Abstract

The diameters of the median neurosecretory cells (MNC) and their nuclei, and the volumes of the corpora cardiaca (CC) and corpora allata (CA) were measured in termites (Zootermopsis angusticollis) of differing age, sex, and caste. The synthetic activities of the MNC and CA were estimated autoradiographically.No significant differences in the diameters of the MNC and their nuclei were observed between insects of differing age, sex, and caste, with the exception of primary reproductives whose MNC are significantly larger than those of larvae of the same instar. The six types of MNC distinguishable histologically differ in their nuclear diameter : cell diameter ratios and in their rates of [3H]uridine and [3H]cystine incorporation.The volumes and (or) synthetic activities of the CA change markedly during the differentiation of reproductives and soldiers. The CA of recently molted primary and supplementary reproductives are several times larger than those of larvae and nymphs of the previous instar, yet their synthetic activity remains low. In contrast, the CA of presoldiers and soldiers are only slightly larger than those of previous instar larvae, but show high synthetic activity. The data are discussed in terms of the endocrine control of caste differentiation.