I don't know. I will refer the question to Glenn Cocking. The ALA says M. aphristis is found in WA but that is not borne out by the Bold Systems 4 distribution.
Lepidoptera Butterfly House says the thorax is white in M. aphristis and shows it is not completely so in a photo of a set specimen of M. desmotoma. A difference may be clear in set moths (see LBH website), but less help in live specimens I expect.
I do not understand why Meyrick, in describing M. aphristis in 1889, made no mention of its similarity to M. desmotoma which he described in 1886. I suspect he had forgotten about his former description, and that M. aphristis is a synonym of M. desmotoma.
I do not understand why Meyrick, in describing M. aphristis in 1889, made no mention of its similarity to M. desmotoma which he described in 1886. I suspect he had forgotten about his former description, and that M. aphristis is a synonym of M. desmotoma.