The two newcomers belong to a group of wasps with a surprisingly dramatic lifestyle. Members of the subfamily Brachistinae are koinobiont ovo-larval endoparasitoids, meaning the female wasp deposits her egg inside the egg or very young larva of a beetle host, most often weevils of the family Curculionidae or tumbling flower beetles of the family Mordellidae. The parasite then develops internally while the host larva continues to grow, only completing its development when the host is full-grown, with a final ectoparasitoid phase. Known hosts of Aliolus species are all weevils, making these tiny wasps potential natural enemies of agricultural pest beetles.

The taxonomic history of the group is nearly as convoluted as its biology. The genera Eubazus, described by Nees in 1812, and Aliolus, described by Say in 1836, share a troubled history spanning more than a century. Martin revised the Nearctic species of Aliolus in 1956, and Mason in 1974 proposed a division based on type species and proper nomenclatural rules, placing Eubazus and Aliolus as valid genera in the tribe Brachistini, then within the subfamily Helconinae, alongside Allodorus and the newly described Nealiolus, while treating Calyptus and Brachistes as subgenera of Eubazus.

The main sticking point has been the metasoma, the rear part of the wasp’s body. Martin and Mason treated Aliolus as a valid genus because its metasoma forms a carapace-like structure, with the first tergite movably joined to the second and the epipleura, the flattened side flaps of the second and third segments, sharply delimited from the dorsal notum. In Eubazus as Mason defined it, the epipleuron is not sharply delimited. But Mason’s own key hinted that the difference is gradual in several species, and in 1990 van Achterberg therefore sank Aliolus as a subgenus of Eubazus, noting that the degree of separation of the third epipleuron from its notum is highly variable even within one species. That observation was based mostly on Palaearctic material, and the variation may be less obvious in Nearctic species.

Opinion has remained split. Papp in 1997 and Sharkey in 1997 kept Aliolus as a valid genus, following Mason’s classification. More recently, molecular phylogenetic work by Sharanowski and colleagues in 2011 and Jasso-Martínez and colleagues in 2022 corroborated the subfamily status of Brachistinae using more genes and more taxa. The 2022 analysis also lent support to treating Aliolus as a genus of its own, because Aliolus and Eubazus did not form a monophyletic clade, meaning the two groups do not appear to share an exclusive common ancestor. However, that study sampled only one species per genus, so the author of the new paper judged it too early to formally change the rank of Aliolus, and the new species are described within Eubazus as the subgenus Aliolus.

Today Aliolus is a medium-sized subgenus with 31 valid Holarctic species, of which 16 were previously known from the Nearctic region. The new study was based on specimens from the Ohio State University Collection of Insects and Spiders, with identification checked against keys by van Achterberg and Sharkey and against publicly available photographs of type specimens held at the Smithsonian National Museum of Natural History. Higher classification follows Chen and van Achterberg in 2019 and Sharanowski and colleagues in 2011, and morphological terminology follows the standard works of van Achterberg and Belokobylskij.

The first new species, Eubazus (Aliolus) confragosus, takes its name from the Latin word for coarse, a nod to the coarsely sculptured basal segments of its metasoma. The female holotype measures 4.0 millimeters long, with a 3.4-millimeter fore wing, and was caught in a Malaise trap at the OSU Barnebey Center between July 9 and 17, 1992, by N. F. Johnson. Three paratypes come from the same site and season, plus one from July 1993. The species is black with yellow palpi, a largely reddish-brown clypeus and face, and yellowish-brown legs. It is distinguished from its closest relative, E. (A.) marginatus, by an evenly curved ventral margin of the clypeus, notauli lacking a wide sculptured area at the rear, and a scutellar sulcus with a single median carina.

The second species, Eubazus (Aliolus) rhyssoeubazus, is larger and more heavily armored in appearance. Its name combines the Greek word rhysso, meaning rugose or wrinkled, with the genus name Eubazus, referring to the strongly wrinkled mesopleuron and the three basal tergites of the metasoma. The holotype female, 5.4 millimeters long with a 4.2-millimeter fore wing, was collected in a Malaise trap at the Barneby Center in late July 1992, with a paratype from early August taken in a flight interception trap by P. W. Kovarik and T. Philips. Its mesopleuron is coarsely rugose-reticulate, its notauli are wide and deep at the rear with a strongly developed median longitudinal carina, and its propodeum bears large tubercles. Males remain unknown. It most resembles E. (A.) fiskei, but differs in those sculptural features and in the shape of the dorsal carinae on the first tergite.

Both species are so far known only from Ohio, and their hosts are unknown, which is typical for this poorly surveyed branch of parasitoid wasp diversity. The study also manually updated the identification key to the Nearctic species of Aliolus, originally built on Martin’s 1956 revision, so that future researchers can separate all 18 regional species, including the two newcomers. One species, E. (A.) sayi, could not be inserted into the key because of uncertainty about its identity.

Discoveries like this underline how much undiscovered diversity can hide in museum drawers, waiting for a specialist with the right keys and microscopes. The work relied on extended-focus imaging with a Leica Z16 APOA microscope and Combine ZP and AutoMontage software, producing detailed illustrations of the head, mesosoma, wings, legs, and metasoma of both species. As molecular datasets grow and more collections are mined, taxonomists expect the map of Nearctic braconid diversity to keep filling in, one overlooked wasp at a time.

Subject of Research: Taxonomic description of two new parasitic wasp species of the braconid subgenus Aliolus from Ohio, United States

Article Title: Two new species of the subgenus Aliolus Say of the genus Eubazus Nees ( Hymenoptera , Braconidae , Brachistinae ) from the United States

Article References: Two new species of the subgenus Aliolus Say of the genus Eubazus Nees ( Hymenoptera , Braconidae , Brachistinae ) from the United States. (n.d.). https://doi.org/10.3897/jhr.99.188661

Image Credits: AI Generated

DOI: 10.3897/jhr.99.188661

Keywords: Eubazus, Aliolus, Braconidae, parasitoid wasps, Hymenoptera, taxonomy, new species, Ohio, Nearctic, Brachistinae, insect collection, natural history