AbstractPostembryonic development of holometabolous and hemimetabolous insects occurs through successive molts triggered by 20‐hydroxyecdysone (20E). The molecular action of 20E has been extensively studied in holometabolous insects, but data on hemimetabolous are scarce. We have demonstrated that during the nymphal development of the hemimetabolous insect Blattella germanica, 20E binds to the heterodimeric receptor formed by the nuclear receptors BgEcR‐A and BgRXR activating a cascade of gene expression, including the nuclear receptors BgE75 and BgHR3. Herein, we report the characterization of BgFTZ‐F1, another nuclear hormone receptor involved in 20E action. BgFTZ‐F1 is activated at the end of each instar, and RNAi has demonstrated that BgHR3 is needed for BgFTZ‐F1 activation, and that BgFTZ‐F1 has critical functions of during the last nymphal instar. Nymphs with silenced BgFTZ‐F1 cannot ecdyse, arrest development, and show structures of ectodermal origin duplicated. BgFTZ‐F1 also controls the timing of the ecdysteroid molting pulse. Developmental Dynamics 237:3179–3191, 2008. © 2008 Wiley‐Liss, Inc.