Abstract We have isolated and sequenced a 1308 bp clone from a pupal brain cDNA library of the flesh fly, Sarcophaga crassipalpis, showing 97% amino acid (aa) sequence similarity to Ceratitis capitata 60S acidic ribosomal protein P0 (CcP0) and 93% aa sequence similiarity to Drosophila melanogaster P0 (DmP0). DmP0 is a multifunctional protein necessary for efficient protein translation of the 60S ribosome as well as DNA repair via AP3 endonuclease activity. In this study, we observed that S. crassipalpis P0 ( ScP0) is cyclically regulated throughout the fly's overwintering pupal diapause. Expression of ScP0 cycles out of phase with the 4 day cycles of O 2 consumption: the peak day of O 2 consumption is characterized by low ScP0 expression, while high expression is noted during the trough of the O 2 consumption cycle. The O 2 cycles, which are in turn driven by cycles of juvenile hormone (JH), can be eliminated by application of a JH analog (JHA). Pupae rendered acyclic with a JHA application consume O 2 at a constant high rate and ScP0 is consistently downregulated. Our findings thus suggest that the cyclic nature of ScP0 regulation during pupal diapause is linked to the JH-mediated metabolic cycles characteristic of this species.