Generic phylogeny of North American Depressariinae (Lepidoptera: Elachistidae) and hypotheses about coevolution

Although a considerable amount of ecological information is known about interactions between Depressaria species and their apiaceous/asteraceous host plants, this information has lacked a phylogenetic context; such a context is important in understanding the evolutionary history and phylogenetic trajectory of plant/insect interactions in general. Accordingly, we undertook an examination of the generic phylogeny of North American Depressariinae, using morphological characters of the larvae, pupae, and adults. Two different parsimony analyses yielded the same tree topology, with a consistency index over 88 and retention index between 90 and 91. This tree provided no evidence of congruent cladogenesis in this group. Host shifts between unrelated host plant families, particularly reversions to ancestral host plant groups, are abundant. Association with plants in Apiaceae and Asteraceae has apparently led to rapid speciation; the two most species-rich taxa, Depressaria Haworth and Agonopterix Hubner, are dominated by species that feed on these families. Because Agonopterix and Depressaria are not sister groups, the Apiaceae must have been colonized independently at least twice by Depressariinae. The best explanation for the pattern of host association seen for genera of depressariine elachistids is that of sequential colonization of related plant groups. This finding is consistent with other findings to date-that congruent cladogenesis is a phenomenon most likely to occur within genera, not at the family or subfamily level.