STUDIES IN THE MODE OF ACTION OF ROYAL JELLY IN HONEYBEE DEVELOPMENT: IV. DEVELOPMENT WITHIN THE BRAIN AND RETROCEREBRAL COMPLEX OF FEMALE HONEYBEE LARVAE

Abstract

Histological evidence is presented for a caste difference in endocrine activity during the critical period of determination in the larval honeybee. Until the last larval instar, neurosecretory cells in the brain of the honeybee larva remain undifferentiated. During this undifferentiated period there is a quantitative difference in apparent activity, as evidenced by the frequency of occurrence of cytoplasmic particles in certain large neuroblasts. Whereas the histological criteria for neurosecretory cells cannot be fulfilled, the brain is presumably exercising a regulatory role in growth and development. These large neuroblasts with phloxinophil inclusions are the likely candidate cells. Between the ages of 40 and 80 hours there is considerably more activity in the queen larva than in the worker. At this time the corpora cardiaca are non-existent as discrete organs.Changes in size and histological appearance of the corpora allata indicate a progressive increase in activity during the first 3 days. In the queen, nuclear degeneration with an apparent cessation of activity occurs in the third and fourth instars. In the late larval and propupal stages a reorganisation occurs. This reorganization is characterized by the reappearance of a discrete nuclear membrane and well-defined nuclei. The presence of intercellular spaces, however, suggests a lack of activity. The corpora allata of worker larvae attain a smaller size during larval life; nuclear degeneration and subsequent reorganization have not been observed in worker larvae.The significance of these caste differences in endocrine activity is discussed.