Stem borer (Coleoptera: Mordellidae) in Campanulastrum

I found a larva overwintering in a lateral stem of a dead stalk of the host in January. During the same winter I also found a few other lateral stems that contained small amounts of whitish frass pellets accumulated near where the branches attached to the main stem. I tentatively identified these frass accumulations as the work of Mordellidae, but was not able to confirm this.

The January larva was fairly young, suggesting larvae may sometimes need to conduct significant feeding in spring (possibly in the main stem) before they reach maturity. Indeed, after I removed it from refrigeration at the end of winter, this larva consumed a significant amount of pith in a piece of host stem provided to it in a rearing container.

The apparent need to feed for a while in the dead stem during the spring of the larva's second growing season is similar to what I have seen in a few other mordellids. For example, the Mordellistena I reared from Aquilegia (record 0067) followed this pattern, and I was even able to rear it to adulthood partly on a diet of Campanulastrum stem pith that I gave it when I ran out of the dead stem material of its original host.