Ecdysone

Ecdysone is a steroid prohormone of the major insect molting hormone 20-hydroxyecdysone. It is secreted from prothoracic glands (or homologous structures in other arthropods) and promotes molting and metamorphosis in arthropods. Chemically, it is a steroidal prohormone of 20-hydroxyecdysone, which is the actual hormone that binds to the ecdysone receptor (EcR).

Ecdysone levels vary throughout the arthropod's life cycle. A surge in ecdysone levels triggers each molt. This process is critical for growth and development, as arthropods possess a rigid exoskeleton that must be shed periodically to allow for increases in size.

In addition to its role in molting, ecdysone plays a role in reproduction, specifically in vitellogenesis (yolk production) in some insects.

Ecdysone and related compounds, collectively known as ecdysteroids, are also found in many plants. While the exact function of ecdysteroids in plants is not fully understood, it is hypothesized that they may act as a defense mechanism against insect herbivores. Some insects have developed mechanisms to tolerate or even utilize these plant ecdysteroids.

The discovery of ecdysone and the elucidation of its hormonal role was a significant breakthrough in understanding insect development and provided a model system for studying hormone action.