Stem borer (Coleoptera: Mordellidae) in Achillea

I found a mordellid larva in a partially frass-filled tunnel in an overwintered dead stem of the host in mid-May. It pupated in the stem, and the adult emerged by mid-June. The larva and pupa were a pale whitish color, with the maturing pupa developing dark eyes, and the adult was a rather nondescript grayish-black color except for a faint reddish wash behind the head.

Mordellistena cervicalis, M. pulchra, and Mordellina pustulata have all been reared from stems of this host in Wisconsin (Lisberg & Young 2003). Of these, both M. cervicalis and M. pulchra may have some reddish coloration on the head and prothorax, according to Liljeblad (1945), which is also a characteristic of my reared adult, but the details of the exact colors involved (which Liljeblad variously referred to as "rufous," "ferruginous," and "reddish yellow") and their extent and patterning differ between those two species (Liljeblad, ibid.), along with other characteristics I have not attempted to compare with my reared adult. Not far from where I collected the larva that gave rise to my adult, Hatfield (2017) collected an adult mordellid with coloration very similar to mine, and she identified her specimen as M. cervicalis based on the leg ridges.