The Ethmiinae is a megadiverse microlepidopteran group comprising 12 genera and more than 350 species worldwide with a complex systematic history at family-level. The core genus Ethmia harbours more than 90% of the diversity with 51 species-groups being proposed. Their major hostplants include Ehretioideae, Boraginoideae and Hydrophylloideae of Boraginaceae plus 8 other angiosperm families. To test the monophylies of both the subfamily and the core genus Ethmia, we reconstructed a phylogeny using 176 species representing 7 genera (i.e. Ethmia, Orophia, Chrysethmia, Pseudethmia, Sphecodora, Pyramidobela and Agrioceros) as the ingroup and including Depressaria and Agonopterix, both belonging to Depressarinae, as the outgroups. In total 115 adult morphological characters (30 binary, 85 multistate) were obtained. To investigate the phylogenetic effect of colour/pattern characters, we partitioned the character dataset into two subsets: “colour/pattern” (58 characters) and “non-colour/pattern” (57 characters). We employed maximum parsimony and successive approximation characters weighting (SACW) to reconstruct the phylogeny and found that neither the subfamily nor the genus Ethmia is monophyletic. The characters relevant to colour patterns generate significant impact on the tree topology, but they do not necessarily cause phylogenetic noise even some of them involve mimicry and aposematism. Optimalization of host associations reveals that the Ethmia moths have colonized Boraginoideae, Hydrophylloideae and Ehretioideae independently, and the diverse non-Boraginaceae associations in North America are more likely derived from the Boraginaceae association independently.