The Eulophidae is a hyperdiverse family within the superfamily Chalcidoidea, comprising roughly 5,300 described species placed in 324 genera and five subfamilies. Eulophids are among the dominant components of parasitoid communities almost everywhere, and many species have been deployed in biological control programmes against agricultural pests. Collectively, their known host spectrum spans more than 100 insect families, and members of the subfamily Tetrastichinae — the group to which the new genus is provisionally assigned and which includes 115 genera — show an especially wide range of lifestyles, including predation on spider eggs and associations with gall-inducing mites.

Against that backdrop, the robust, armoured abdomen of Chelonastichus stands out sharply. The metasoma of the female is transformed into a strong carapace formed by a greatly enlarged fifth gastral tergite, Gt5, which is coarsely sculptured and setose, while the second to fourth tergites are very short. The sixth and seventh tergites are strongly reticulate and retracted beneath the carapace, and the seventh bears a triangular posterior process.

This configuration means that the bulk of the abdomen's surface is covered by a single hardened, shield-like plate — an arrangement that has never before been recorded in the family. The authors note that the specimen was dried using hexamethyldisilazane, or HMDS, a technique that prevents the collapse of delicate bodies, before being card mounted, imaged with a multifocus stereo microscope system, and deposited as the holotype in the Insect Museum of the Chulalongkorn University Museum of Natural History in Bangkok. Carapace-like abdomens have evolved repeatedly in other parasitoid wasp lineages, which makes the new find both surprising and instructive.

Heavily sculptured metasomal carapaces have arisen on numerous occasions within the family Braconidae and, far more rarely, in the Ichneumonidae. Within the Chalcidoidea itself, several families contain genera in which one or more gastral tergites are considerably enlarged — often the first tergite, while members of the Diapriidae, Eucharitidae, Moranilidae and Perilampidae typically have the second tergite enlarged so that it largely conceals the more posterior segments. Crucially, however, in none of those cases is the resulting carapace heavily sculptured.

Among chalcidoids, only male leucospids come close, with the second to fifth tergites fused into a highly sclerotised and sculptured carapace. As far as the authors can determine, the new species represents the first example in the entire superfamily of a heavily sculptured carapace formed from the fifth gastral tergite. The generic name Chelonastichus reflects this anatomical novelty.

It combines Chelonus, a well-known genus of braconid wasps famed for its carapace-like metasoma, with the suffix astichus, a nod to the subfamily Tetrastichinae, in which the new genus is provisionally placed. The species epithet hanssoni honours Dr Christer Hansson of Lund University in Sweden, recognising his outstanding contributions to the study of Eulophidae. Placing the new genus within Tetrastichinae required careful comparative anatomy.

The authors justify the provisional placement on the basis of several characters: the axillae are strongly angularly advanced, the postmarginal vein of the fore wing is absent, and the submarginal vein is not smoothly continuous with the parastigma. Yet Chelonastichus departs from the typical tetrastichine blueprint in notable ways. Most tetrastichines carry distinct submedian longitudinal grooves on the mesoscutellum, but in the new genus these grooves are almost indistinct.

The genus also shows affinities with Aceratoneura from Australia and the widespread Old World genus Sigmophora, sharing with them a transverse carina behind the lateral ocelli, but it differs from Aceratoneura in the number of funicular segments of the antenna and from Sigmophora in the number of anelli — the tiny ring-like segments at the base of the antenna — in addition to being separated from both by its greatly enlarged Gt5. The head bears a complete, straight malar sulcus, a convex clypeal margin without teeth, and bidentate mandibles with a wide upper tooth and an acute lower one. The frons is shiny, with transverse striae anterolaterally associated with fine reticulations and a transverse median carina, while the vertex is finely reticulate with a more or less complete transverse carina.

The antenna consists of two anelli, three funicular segments and three clavomeres with a weak constriction between the first and second. On the mesosoma, the pronotum carries long setae and is distinctly reticulated and shiny; the mesoscutum has a distinct median groove in its anterior two-thirds and one pair of long, strong adnotaular setae posteriorly; the notauli are complete without crenulations; and the axillae are advanced by half their length in front of the transscutal articulation. The propodeum features a wide, short fovea behind the dorsellum and a complete, strong, narrow median carina that expands into a triangular shape posteriorly.

The wings and legs add further diagnostic detail. The fore wing is entirely hyaline, with four setae on the dorsal surface of the submarginal vein, an absent postmarginal vein, and a very narrow costal cell that is 13 times as long as wide. The speculum is open, the stigmal vein carries four campaniform sensillae, and the posterior margin of the hind wing bears long setae.

The body of the holotype is yellow except for reddish eyes and ocelli, a brownish-orange antennal clava, and brown second to fourth gastral tergites. Precise morphometric ratios — from head width-to-length proportions to the relative lengths of antennal segments and wing veins — accompany the description, following the terminological conventions of LaSalle from 1994 and Harris's 1979 system for cuticular sculpture, ensuring that future workers can compare the species rigorously with its relatives. Why would a eulophid evolve such an armour-plated abdomen?

The authors point to a pattern observed across parasitoid wasps: the possession of a metasomal carapace is often associated with oviposition into something hard, such as an insect egg or pupa, or a plant gall. This correlation, drawn from earlier work on carapace-bearing braconids and ichneumonids, offers a plausible — though unconfirmed — hint about the biology of the new species. Unfortunately, the biology of Chelonastichus hanssoni remains entirely unknown; no host records exist, and the species is known only from the single trapped female from Thailand, within the Oriental region.

A single specimen has revealed an anatomical innovation — a heavily sculptured carapace built from the fifth gastral tergite — that is unique across a family of more than 5,000 described species and a superfamily of staggering global diversity.

Subject of Research: Description of a new genus and species of eulophid wasp from Thailand with the first known metasomal carapace in the family Eulophidae

Article Title:  Chelonastichus Ranjith & Quicke, gen. nov. ( Hymenoptera , Eulophidae , Tetrastichinae ) from Thailand: the first eulophid with a metasomal carapace

Article References: Ranjith, A. P., Quicke, D. L. J., Chansri, K., & Butcher, B. A. (2025). Chelonastichus Ranjith & Quicke, gen. nov. (Hymenoptera, Eulophidae, Tetrastichinae) from Thailand: the first eulophid with a metasomal carapace. Journal of Hymenoptera Research, 98, 499-507. https://doi.org/10.3897/jhr.98.144864

Image Credits: AI Generated

DOI: 10.3897/jhr.98.144864

Keywords: Chelonastichus hanssoni, Eulophidae, Tetrastichinae, Chalcidoidea, parasitoid wasp, Thailand, new genus, metasomal carapace, taxonomy, Hymenoptera, Malaise trap, Sakaerat