2 Social Insect Polymorphism: Hormonal Regulation of Plasticity in Development and Reproduction in the Honeybee

This chapter discusses the hormonal regulation of plasticity in development and reproduction in the honeybee. The insight that hormones may be the cornerstones for understanding the developmental regulation, not only in preimaginal caste differentiation but also in adult life, has turned honeybee into a model for studies on caste in social insects, the reasons being its relatively large size and its ready availability together with a wealth of knowledge concerning honeybee biology and management. More recent views on caste differentiation seek to understand the developmental regulation in honeybee in the context of metamorphosis, particularly focusing on the role of the morphogenetic hormones, juvenile hormone, and ecdysone. These hormones exert additional and apparently novel functions in the adult life of honeybee. Reproduction and division of labor are also discussed in the chapter in the context of endocrine regulation. Long-term integration of the developmental processes and reproduction cycles with environmental conditions poses a key problem for any organism. In general, the required interaction of external stimuli with the genotype of an organism is mediated and orchestrated by hormones. During critical periods of caste differentiation, research on the regulatory pathways in the endocrine system of the honeybee larvae has shown that the corpora allata exhibit a caste-specific program of activity during the last larval instar and that this program can set the activity pattern of the prothoracic gland.