The accumulation of many edited mRNAs is developmentally regulated in a transcript-specific fashion in Trypanosoma brucei. In addition, these transcripts are frequently present in two size classes which differ substantially in the lengths of their poly(A) tails, and poly(A) tail length is also developmentally regulated. Previously, these phenomena have only been studied in the mammalian bloodstream and insect procyclic forms (BF and PF, respectively) of T. brucei. In this paper, we examine developmental regulation of edited RNA abundance and poly(A) tail length of 3 mitochondrially encoded RNAs in mammalian BF and 3 insect stages (PF, epimastigotes, and metacyclics) of T. congolense. T. congolense BF and PF are similar, but not identical, to these stages of T. brucei with regard to edited RNA accumulation and poly(A) tail length. At the level of edited RNA, both epimastigotes and metacyclic stage parasites appear to be pre-adapted for the respiratory mechanisms of BF but not yet down-regulated from the cytochrome-based respiration of PF since edited RNAs encoding NADH dehydrogenase components are up-regulated and edited CYb RNA is abundant in these stages. Poly(A) tail lengths of mitochondrial mRNAs appear to be regulated independently of edited RNA abundance. These results indicate that multiple mechanisms for regulation of mitochondrial gene expression are active throughout the trypanosome life cycle.