The discovery, published in the Deutsche Entomologische Zeitschrift, is the work of a researcher who combined classical taxonomy with cutting-edge phylogenomics to characterise the new species. The holotype, a well-preserved male, was hand-collected during a 2014 field trip by Drs. M. Hauser and N. von Ellenrieder in Vĩnh Phúc Province, near the Thien Nhi Mountain just north of Tam Đảo town. The ridge on which Thien Nhi Mountain sits forms the border with Thái Nguyên Province, and the surrounding landscape falls largely within Tam Đảo National Park, a protected area harbouring tropical montane evergreen forests of great conservation value.

Tam Đảo is a biogeographic treasure trove. Rising to altitudes above 1,500 metres, the range sits in a transition zone between tropical and cooler subtropical climates, with seasonal rainfall concentrated from May to September and pronounced winters. Surrounded by densely populated lowlands, the mountains preserve islands of undisturbed habitat that have yielded a remarkable diversity of plants, vertebrates and invertebrates. Many species described from Tam Đảo bear the epithet tamdaoensis, including numerous insects, reptiles and plants, and the new bee now joins their ranks, named in honour of its type locality and its famous species diversity and endemism.

Gnathonomia is a genus endemic to Southeast Asia, first described in 2005 using an unpublished manuscript name of the late Dr. Donald B. Baker, a renowned bee taxonomist. The type species is Nomia nasicana Cockerell, 1911, which is a junior synonym of Nomia aurata Bingham, 1897. The genus is characterised by a combination of morphological features: some species have integumental bands on the apical margins of the metasomal terga, a common character in the subfamily Nomiinae; they lack projections on the metanotum, which differentiates them from Hoplonomia and Crocisaspidia; females have a completely delimited basitibial plate, unlike Nomia s. str. and Leuconomia; and the tegulae are small and oval rather than enlarged and ear-shaped as in Curvinomia or Maculonomia.

What makes Gnathonomia truly distinctive, however, is the unusually modified morphology of the clypeus and mandibles in males. With the exception of G. mayoyaoensis from the Philippines, all males possess a pronounced subapical tooth along the inner margin of the mandible, giving it a distinct fork-like shape. Males of several species also have a noticeably concave anterior margin of the clypeus, sometimes clearly incised, and an unusually long labrum. These elaborate head structures likely play a role in male mating behaviour, although direct observations remain scarce for most species in the genus.

Gnathonomia tamdaoensis stands apart from all its relatives by virtue of a conspicuous median, downward-facing, pointed projection on the male clypeus, a feature not seen in any other known species of the genus except G. cambodiana, which has a differently shaped, squared and parallel-sided shelf-like lamella that is not downward-facing. The new species also lacks the coloured integumental bands on the metasomal terga found in many relatives, has a greatly inflated, nearly triangular hind femur, and possesses a large, bilobed apical projection on the hind tibia that is uniquely shaped. The combination of these features, together with its enormous body size, makes it not obviously comparable to any other described Gnathonomia.

To place the new species in an evolutionary context, the researcher turned to whole-genome sequencing. DNA was extracted from a single mid-leg of the holotype, broken off below the femur, in a minimally destructive approach that preserved the specimen for morphological study. Sequencing on an Illumina NovaSeq X Plus generated nearly 89 million short reads, which were assembled into a genome of 288.22 megabases across almost 92,000 contigs with an average coverage of nearly 38-fold. A BUSCO assessment, which evaluates the presence of 5,991 single-copy orthologous genes shared across Hymenoptera, found 78.3 percent complete and single-copy genes, indicating a reasonably complete assembly despite the low-coverage approach.

From these genomic data, the researcher extracted ultraconserved elements, or UCEs, using the Phyluce pipeline and the bee-ant-specific hym-v2 bait set, requiring 80 percent overlap and identity. This yielded 2,382 out of 2,545 UCE loci, which were combined with data from 65 previously generated assemblies spanning the Nomiinae. Maximum Likelihood phylogenetic reconstruction recovered a topology congruent with previous estimates, placing Gnathonomia as monophyletic and nested within a group of African lineages. Gnathonomia tamdaoensis was found as sister group to the remaining species of the genus, confirming the morphology-based genus concept of Pauly and providing evidence for the close relationship to other Gnathonomia species.

The phylogenetic position of Gnathonomia within a clade of predominantly African lineages is remarkable. Previous phylogenomic work indicated a close evolutionary relationship to the African-endemic genus Trinomia, with a divergence estimated in the late Miocene around 12 million years ago. This disjunct distribution, with related lineages separated by the vast expanse of the Indian Ocean and the Arabian Peninsula, is not entirely unusual for the subfamily Nomiinae, which comprises about 630 described species globally, roughly 610 of which occur in the Palaeotropics, Palearctic and Australasia compared to only 17 in the Nearctic and none in South America. Several other nomiine genera of comparable antiquity, including Lipotriches, Steganomus, Pseudapis and Pachynomia, have representative species in both the Afrotropic and Oriental realms, although no single species seems to inhabit both regions simultaneously today.

Despite the wealth of molecular and morphological information now available for Gnathonomia tamdaoensis, much about its biology remains unknown. No observational data exist for the species, and no flower visit has been recorded. The single known specimen was collected in mid-June, coinciding with the rainy season and elevated temperatures in northern Vietnam. The female remains unknown, which is not unusual for the genus, as multiple species are very difficult, if not impossible, to separate using females alone, and the genus concept relies heavily on male characters for species identification. Given that the more informative male was available for study, the decision to describe the new species despite the unavailable female reflects the exceptional distinctiveness of the specimen. The holotype is temporarily deposited in the California State Collection of Arthropods and will ultimately be transferred to the Vietnam National Museum of Nature in Hanoi, ensuring that this giant of the Tam Đảo mountains will be preserved and accessible for future generations of researchers.

Subject of Research: Evolutionary history of Gnathonomia tamdaoensis sp. nov., a new bee species from Vietnam ( Hymenoptera , Halictidae )

Article Title: Evolutionary history of Gnathonomia tamdaoensis sp. nov., a new bee species from Vietnam ( Hymenoptera , Halictidae )

Article References: Bossert, S. (2026). Evolutionary history of Gnathonomia tamdaoensis sp. nov., a new bee species from Vietnam (Hymenoptera, Halictidae). Deutsche Entomologische Zeitschrift, 73(1), 171-179. https://doi.org/10.3897/dez.73.179341

Image Credits: AI Generated

DOI: 10.3897/dez.73.179341

Keywords: Evolutionary, history, Gnathonomia, tamdaoensis, species, Vietnam, Hymenoptera, Halictidae, scientific research