The epitracheal endocrine system and associated signalling cascades in development, reproduction, and behaviour

Abstract The epitracheal endocrine system is a network of glands whose functions during larval development are critical for initiation and scheduling of the ecdysis sequence at the end of each moult in insects. Ecdysis triggering hormones (ETHs) released from Inka cells recruit a cascade of downstream chemical signaling events that coordinate tracheal airfilling and sequential behaviours. Genes encoding ETHs and corresponding receptors are induced early in the molt by ecdysteroids, while Inka cell secretory competence depends upon late gene expression during steroid decline. During adulthood, ETH signaling is repurposed for reproductive functions, including promotion of vitellogenesis and ovulation in females and courtship memory in males. Some of these physiological actions depend upon ETH acting as a juvenile hormone promoting allatotropin. Emerging functions for ETH signaling include regulation of water balance, stress responses, and olfactory-mediated behaviours.