Insects are incapable of synthesizing the steroid ring. Obtain plant sterols in the diet. Produced and secreted by prothoracic gland . Located in the first thoracic segment. Ecdysone secreted during larval and pupal stages.
Gland regresses in adult.
Causes differentiation of tissues in direction of adult form. Ecdysone causes swelling of specific regions of chromosomes from midge salivary gland. These puffs are areas of increased RNA synthesis. First direct evidence that a steroid hormone directs the activity of specific genes. Dependent on an external signal, such as changing environmental temperature.