Caste-specific maturation of the endocrine system in the female honey bee larva.

The endocrine system of female honey bee larvae has been studied through postembryonic development with histological and autoradiographic techniques. During larval development, brain and retrocerebral complex proceed from immature cells to an active endocrine system. Caste-specific retardation occurs in the worker during this process. In the developing queen, the differentiation of the neurosecretory cells (NSC) and the outgrowth of their axons occurs from the second instar onward and is nearly completed in the fourth, whereas in the worker larva these processes are delayed by more than one instar. In the queen, RNA synthesis starts in the NSC at the end of the third instar and in the worker at the fifth instar. Stainable neurosecretory material is present only in fifth instar queen larvae. The queen's corpora cardiaca become active at the end of the fourth, those of the worker in the fifth instar. In the corpora allata (CA), nuclei undergo several phases of endomitosis. These phases of polyploidization end at the beginning (queen) or at the end (worker) of the fifth instar respectively. CA volume in the queen is twice that of a worker at its height at the end of larval development. these data demonstrate a caste-specific maturation of the endocrine organs which results in differences in hormone titres.