Stem borer (Coleoptera: Mordellidae) in Baptisia

I found larvae overwintering in dead stems of the host in a remnant prairie in late April, 2018. They had fed in the pith while the stems were still alive in the previous growing season. Larval tunnels occasionally strayed near the surface of the stem, resulting in short, irregular, externally visible mines, before reentering deeper tissues. Tunnels in the stem interior showed extensive accumulation of fine powdery frass. Adults emerged in early June. Using photos, Belov (2020) identified an adult to tribe on the BugGuide website.