ecdysones

Ecdysones, or ecdysteroids, are a class of steroid hormones that regulate molting and metamorphosis in arthropods, most notably insects. The hormone ecdysone is produced by the prothoracic glands and is often converted in target tissues to the most active form, 20-hydroxyecdysone, which orchestrates developmental transitions such as larval molts and the progression to pupal and adult stages.

In insects, ecdysones act through a nuclear receptor complex formed by the ecdysone receptor (EcR) and the ultraspiracle protein (USP). Upon binding, this receptor complex functions as a transcription factor, modulating the expression of genes involved in cuticle synthesis, tissue remodeling, and other processes essential for molting. The timing and amplitude of ecdysteroid pulses interact with juvenile hormone levels to determine the developmental outcome (larval molt versus metamorphosis).

Ecdysones occur broadly in arthropods, including insects and some crustaceans, where they regulate growth and development. They are also found in plants as phytoecdysteroids, compounds that resemble insect ecdysteroids and can affect herbivores that feed on the plants. In plants, these compounds are thought to serve as chemical defenses, deterring or harming insect herbivores.

Applications of ecdysones and their mimics include the use of insect growth regulators in pest management. Synthetic ecdysone receptor agonists, such as certain but widely used agrochemicals, disrupt normal development in targeted pest species without causing immediate mortality, reducing populations by preventing successful maturation.

Ecdysones are distinct from juvenile hormone, which primarily controls developmental timing and metamorphosis through a different signaling pathway.