SUMMARYQueens and workers of the honey bee, Apis mellifera. have been reared as larvae and pupae under defined conditions, and the developmental stages have been associated with unequivocal features. The larval instars are characterized by the head diameter and weight of the larvae. The stages of pupal development. are defined by the colours shown by the compound eyes and the thorax. The temporal duration of the successive developmental stages has also been determined. With these criteria a larva or a pupa can be assigned to a definite position on the developmental time axis.
The endocrine system of the honey bee (Apis mellifera L.) has been studied morphologically through post-embryonic development with several histological techniques. Marked differences in the structure of the neurosecretory complex of queen and worker larvae have been observed during larval stages. In queen larvae, morphogenesis of the neurosecretory cells, their axons and the formation of the chiasma takes place during end of 2nd and beginning of 3rd, in the workers at beginning of 4th larval instar. Stainable neurosecretory material was found in queen larvae at the beginning, in worker larvae at the end of 4th instar. In early larval stages, the corpora allata are more active in the queen. During initial 3 - 5 days of larval development the gland volume is reduced in both castes. After 36 to 48 hours of endocrine retardation, the glands become active again. The same histological effects are found under experimental conditions, where worker larvae of 2nd instar were reared in the incubator on basic food, Royal Jelly and with topically applied juvenile hormone I.
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.
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