Research paperThe complete mitogenomes of Calameuta filiformis (Eversmann, 1847) and Calameuta idolon (Rossi, 1794) (Hymenoptera: Cephidae): The remarkable features of the elongated AÂ +Â T rich region in Cephini

•The complete mitogenomes of stem borers, Calameuta filiformis and Cl. idolon, are sequenced and characterised.•A rearrangement in IQM gene cluster and a length expansion in rrnS gene are suggested as synapomorphies for Cephini.•A remarkable length increase is also observed in their A + T rich region.•Characterisation of the A + T-rich region reveals the presence of the tRNA- and rRNA-like sequences and tandem repeats.•Short tandem repeats are suggested replication fork barrier in insects for the first time.

Two complete mitogenomes of the stem borers, Calameuta filiformis and Calameuta idolon, and the complete A + T-rich region of Trachelus iudaicus (Hymenoptera: Cephidae), are reported. The mitogenomes of these species are the longest reported from hymenopterans to date. A remarkable increase in length of the A + T-rich region, the longest for Hymenoptera, was found and compared across the tribe Cephini. The presence of the tRNA- and rRNA-like sequences were reported in the A + T-rich region of sawflies and they were suggested to play a role in replication and/or transcription. The long and short tandem repeats were orderly located in both sides of the A + T-rich region producing stable secondary structures. We suggest that the short tandem repeats are likely to function as a replication fork barrier.