Stem borer (Coleoptera) in Boechera

Four sprawling lateral stems of the hostplant I observed in late June 2023 contained extensive tunneling in the lower parts of the stems. There was generally little or no frass in the upper parts of the tunnels; in the lowermost parts, closest to the base of the stems, compacted frass could sometimes be found in abundance, but not in all tunnels examined. In one example, the bottom ~80mm of stem had been tunneled, and a parasitoid cocoon was found in the tunnel near its upper end, several centimeters from the discarded remains of the beetle larva that had evidently served as its host. In a second example, a tunnel contained a parasitoid cocoon right next to the host's remains. In each of these two cases the host's remains included the complete head capsule of the larva, which was clearly identifiable as Coleoptera. I did not observe live larvae or other stages of this borer.