During the screening of immune-regulated genes from the cabbage looper, Trichoplusia ni, a 3-dehydroecdysone 3beta-reductase homologue (DERH) was cloned. In the course of development, 3-dehydroecdysone 3beta-reductase mediates the conversion of 3-dehydroecdysone (3dE) secreted from the prothoracic