Stem borer (Lepidoptera: Pterophoridae) in Solidago

In Solidago cf. canadensis, the larva tunnels in the lower stem and, when at or near maturity, severs the stem ~10-35 cm above ground level, causing the upper part of the plant to break off and leaving a lower stem "stump" with the larva inside. My observations show that the outer walls of the stem at the tip of the stump sometimes have a beveled edge, having been cut by the larva at an angle (see photos). After making the cut and allowing the top of the stem to break off, the larva seals the open end of the stump with a plug of frass. Larvae overwinter in stem stumps at ground level. In spring, prior to pupation, a larva I kept in its stem stump in a rearing container removed the frass plug from the stump, making way for the eventual emergence of the adult moth. I reared two adults in May 2017, and one of these was identified as H. glenni by D. Matthews from photos.

In August 2023, I observed a young Hellinsia larva in a stem of elmleaf goldenrod, S. ulmifolia. The larva dwelled in its gallery in the pith of the lower stem and expelled frass through a small round hole in the outer wall of the stem. I am unsure if this S. ulmifolia feeder is the same species as the one described above from stems of S. canadensis complex.