DNA barcodes reveal inconsistent species boundaries in rose gall wasps Diplolepis and their inquilines Periclistus (Hymenoptera: Cynipidae)

Rose gall wasps Diplolepis induce structurally distinct galls on wild roses, which provide gallers with food and shelter. These galls are attacked by a wide variety of micro-hymenopterans including another cynipid Periclistus that act as inquilines. Both Diplolepis and Periclistus are difficult to distinguish based on adult morphology, instead the structural appearance of galls is often used to distinguish species. Using the mitochondrial gene COI, we built phylogenies of both Diplolepis and Periclistus, while also estimating the ancestral host use of the inducers. Our phylogeny recovered the monophyly of Diplolepis, which have likely diverged from single-or multi-chambered leaf gallers to other plant organs. Periclistus exhibits a divide between the Palearctic and Nearctic clades, and ranges from specialists to generalists in terms of host specificity. The molecular results have largely supported the validity of species described in the literature, with notable exceptions in four species groups. While it is premature to enact any taxonomic changes without additional molecular markers, this incongruence between morphological and molecular data indicates these groups need taxonomic revision and gall morphology alone may be inadequate to delimit species.