The evolutionary history of mammoth wasps (Hymenoptera: Scoliidae)

Scoliid wasps comprise a clade of aculeate insects whose larvae are parasitoids of scarabaeid beetle grubs. While scoliids have been studied and used as biological control agents, research into the groups evolution, as well as the stability of scoliid taxonomy, has been limited by a lack of reliable phylogenies. We use ultraconserved element (UCE) data under concatenation and the multispecies coalescent to infer a phylogeny of the Scoliidae. In order to mitigate potential issues arising from model misspecification, we perform data filtering experiments using posterior predictive checks and matched-pairs tests of symmetry. Our analyses confirm the position of Proscolia as sister to all other extant scoliids. We also find strong support for a sister group relationship between the campsomerine genus Colpa and the Scoliini, rendering the Campsomerini non-monophyletic. Campsomerini excluding Colpa (hereafter Campsomerini sensu stricto) is inferred to be monophyletic, with the Australasian genus Trisciloa recovered as sister to the remaining members of the group. Out of nine genera in which more than one species was sampled, Campsomeriella, Dielis, Megascolia, and Scolia are inferred to be non-monophyletic. Analyses incorporating fossil data indicate an Early Cretaceous origin of the crown Scoliidae, with the split between Scoliini + Colpa and Campsomerini s.s. most probably occurring in the Late Cretaceous. Posterior means of Scoliini + Colpa and Campsomerini s.s. crown ages are estimated to be in the Paleogene, though age 95% HPD intervals extend slightly back past the K-Pg boundary, and analyses including fossils of less certain placement result in more posterior mass on older ages. Our estimates of the stem ages of Nearctic scoliid clades are consistent with dispersal across Beringia during the Oligocene or later Eocene. Our study provides a foundation for future research into scoliid wasp evolution and biogeography by being the first to leverage genome-scale data and model-based methods. However, the precision of our dating analyses is constrained by the paucity of well-preserved fossils reliably attributable to the scoliid crown group. Despite concluding that the higher-level taxonomy of the Scoliidae is in dire need of revision, we recommend that taxonomic changes be predicated on datasets that extend the geographic and taxonomic sampling of the current study.