Ecdysone is a[clarification needed] prohormone of the major insect molting hormone 20-hydroxyecdysone, secreted from the prothoracic glands.

Ecdysteroids act as moulting hormones of arthropods but also occur in other related phyla where they can play different roles.

[1][2] In Drosophila melanogaster, an increase in ecdysone concentration induces the expression of genes coding for proteins that the larva requires.

Recent findings in the laboratory of Chris Q. Doe have found a novel role of this hormone in regulating temporal gene transitions within neural stem cells of the fruit fly.

[3] Ecdysone and other ecdysteroids also appear in many plants mostly as a protection agent (toxins or antifeedants) against herbivorous insects.