From two putative inquilines to one definitive parasitoid: clarifying feeding ecology and species limits in Nearctic Euceroptres Ashmead, 1896 wasps (Hymenoptera: Figitidae).

Oak galls are structures of modified plant tissue, induced by an ovipositing female oak gall wasp (Hymenoptera: Cynipidae: Cynipini), that provide food and shelter for her progeny. Myriad other wasp species exploit galls, feeding on either the gall wasp larva (parasitoidism), the gall tissue (inquilinism/kleptoparasitism), or other parasites within the gall (hyperparasitism). Though many oak gall-associated wasps are now described, their feeding ecology often remains poorly documented, particularly in the species-rich communities across North America. Wasps in the genus Euceroptres (Hymenoptera: Figitidae) exemplify this problem, long having been assumed to be inquilines based on limited evidence. We used dissections, microcomputed tomography scanning, and DNA barcoding to discover that Euceroptres do not modify the internal composition of their host gall. We also found a Euceroptres larva feeding on gall-inducer larva within an unaltered gall wasp larval chamber. Thus, Euceroptres are parasitoids, not inquilines. While sequencing larval and adult Euceroptres, we also found that the 2 previously described species in eastern North America, Euceroptres whartoni Buffington and Liljeblad, 2008 and Euceroptres primus Ashmead, 1896, did not separate into distinct clades, suggesting they are a single species. Subsequent morphological comparisons support this finding, allowing the establishment of E. whartoni as a syn. nov. of E. primus.