Hormonal Circuits for Homeostatic Regulation of Energy and Water Balances in Insects

Organisms adjust their growth, development, physiology, metabolism, and behavior in response to internal and environmental fluctuations to enhance their chances of survival and reproduction. In animals, specialized cells and/or organs detect these fluctuations and release endocrine factors that regulate growth and homeostatic responses. One of the major functions of these endocrine factors is to maintain energy and water balance. In insects, energy (metabolic) homeostasis, which is crucial for facilitating adult physiology, is primarily regulated by insulin signaling for energy uptake and glucagon-like adipokinetic hormone for energy mobilization. Water (osmotic) homeostasis is achieved through a balance between diuretic hormones (DHs) and antidiuretic hormones (ADHs), which optimize osmoregulatory responses. Notably, osmoregulatory circuits interact with metabolic homeostasis networks, highlighting that these hormonal pathways integrate osmotic and metabolic regulation. Conventional DH and ADH pathways play a pivotal role in regulating metabolic homeostasis and influencing behaviors that indirectly affect metabolic outcomes. This interplay suggests that these hormonal circuits coordinate both water balance and metabolic regulation. This chapter overviews the action of these hormones as systemic regulators, providing a framework for understanding how metabolic and osmotic homeostasis are orchestrated to achieve optimal systemic regulation.