Investigating the systematics of the Pseudochalcura gibbosa (Hymenoptera: Eucharitidae) populations of North America

Pseudochalcura gibbosa Provancher (Chalcidoidea: Eucharitidae) is a widespread Nearctic species of wasp that is parasitic upon Camponotus (carpenter ant) brood. Populations of P. gibbosa can be found across the entirety of the United States and as far north as the Yukon and Alaska. As with all eucharitids, eggs are laid into plant tissue away from the host. Upon emergence, larvae are encountered by foraging ants and passively transported back to the ants’ brood, where they initially attach to the ant larvae and begin development on the pupae. Based on morphological analyses, two previously described Nearctic species, P. californica (Ashmead) and P. arizonensis (Crawford), were synonymized under P. gibbosa. The goal of this research is to revisit these synonymies with P. gibbosa by using molecular comparisons based on combined ribosomal 28S-D2 and mitochondrial cytochrome oxidase I sequence data sampled from more than 25 individuals across six genera of Eucharitinae. The results provide evidence for the existence of cryptic species within the currently defined P. gibbosa. A new plant host, Rhododendron occidentale (Torrey & A. Gray) A. Gray (Ericaceae) (western azalea), is recorded from a recently discovered population of P. gibbosa from the central Sierra Nevada Mountains of California. This indicates a close relationship with other known populations from the western U.S. and Canada that also utilize Rhododendron for oviposition. The preference of other host plants, such as Seranoa (saw palmetto) among P. gibbosa from Florida, offers further evidence of the presence of multiple species.