Ecdysone Metabolism in Insects

The current status of the pathway of ecdysone biosynthesis andinactivation in insects is discussed. Evidence is presenteddemonstrating that rß-ecdysone is generated from -ecdysoneby fat body, Malpighian tubules, gut, and body wall, but notby blood, oenocytes, muscle, salivary gland, or the prothoracicgland itself (in vitro experiments with prepupal Manduca sextatissues). Since -ecdysone does not appear to have demonstrablehormonal activity at physiological concentrations in in vitrotissue systems which cannot metabolize it to rß-ecdysone,it is suggested that -ecdysone serves as a prohormone ratherthan as a hormone. The role of the prothoracic gland in theproduction of -ecdysone remains to be defined.