Taxonomy and phylogeny of the A sphondylia species ( D iptera: C ecidomyiidae) of N orth A merican goldenrods: challenging morphology, complex host associations, and cryptic speciation

Reproductive isolation and speciation in herbivorous insects may be accomplished via shifts between host‐plant resources: either plant species or plant organs. The intimate association between gall‐inducing insects and their host plants makes them particularly useful models in the study of speciation. N orth A merican goldenrods ( A steraceae: S olidago and E uthamia ) support a rich fauna of gall‐inducing insects. Although several of these insects have been the subject of studies focusing on speciation and tritrophic interactions, others remain unstudied and undescribed. Among the latter are at least seven species of the large, cosmopolitan gall midge genus A sphondylia   L oew ( D iptera: C ecidomyiidae), the taxonomy and biology of which are elucidated here for the first time using morphological, molecular, and life‐history data. We describe Asphondylia pseudorosa  sp. nov. , Asphondylia rosulata  sp. nov. , and Asphondylia silva  sp. nov. , and redescribe A sphondylia monacha   O sten S acken, 1869 and A sphondylia solidaginis   B eutenmüller, 1907, using morphological characters of adults, immature stages, and galls, as well as sequence data from both nuclear and mitochondrial genes. A neotype is designated for A . solidaginis , the type series of which is considered lost. We also provide information on the life history of all species, including a description of two inquilinous cecidomyiids commonly found in the galls, Clinodiplosis comitis  sp. nov. and Y oungomyia podophyllae ( F elt, 1907), and on parasitoid wasps associated with the gall midges. A sphondylia johnsoni Felt, 1908, which was described from an unknown gall on an unknown S olidago host, is assigned to nomina dubia . Our phylogenetic analyses show that some of the A sphondylia species associated with goldenrods induce two different types of galls during their life cycle, some exhibit host alterations, and some do both. In the absence of reliable morphological differences, recognising species boundaries and deciphering host associations of species must rely heavily on molecular data. Our analysis suggests that radiation in this group has been recent and occurred through shifts among host plants. © 2015 The Linnean Society of London