Insect metamorphosis is regulated by ecdysteroids, which induce molts, and juvenile hormone (JH), which inhibits metamorphic changes. The molecular action of ecdysteroids has been thoroughly studied, but that of JH is poorly understood, with data currently only being available for holometabolous species, like Drosophila melanogaster and Tribolium castaneum. We studied the function of Krüppel homolog 1 (Kr-h1) in Blattella germanica, a hemimetabolous model. Kr-h1 is a Zn finger transcription factor whose function as transductor of the antimetamorphic action of JH has recently been demonstrated in D. melanogaster and T. castaneum. The RNAi experiments reported herein indicated that Kr-h1 transduces the antimetamorphic action of JH also in B. germanica, thereby suggesting that this role is an ancestral condition that has been conserved in insect evolution from hemimetabolous to holometabolous species.