Megaspilidae is a globally distributed family of small parasitoid wasps, occurring across all major biogeographic regions except Antarctica. Members of the family can be recognized by a suite of diagnostic features: a forewing with a well-developed large pterostigma, a curved radial sector crossvein in the forewing, two apical spurs on each tibia, and a mesoscutum that typically bears three longitudinal furrows, sometimes reduced. More than 450 valid species in 12 genera are currently recognized worldwide, and recent intensive revisions indicate that a large proportion of the family’s species diversity remains undescribed. The genus Conostigmus, established by Dahlbom in 1858 and initially treated as a subgenus of Megaspilus before being elevated to generic rank by Kieffer in 1907, is the most species-rich and widely distributed genus within the family, with approximately 190 valid described species and its highest diversity concentrated in the Palaearctic region.

China’s Conostigmus fauna has remained comparatively poorly documented. Only 17 species had been formally recorded from the country before this study, despite the genus’s strong Palaearctic diversity. Diagnostic characters for the genus include cylindrical male flagellomeres, a female first flagellomere less than 1.5 times as long as the pedicel, and an ocular ocellar length equal to or greater than the posterior ocellar length. One persistent complication in studying these wasps is that strong sexual dimorphism is widespread in Conostigmus, which often makes morphological association of conspecific males and females difficult or unreliable. For this reason, DNA barcode data, especially sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene, have become increasingly important for confirming conspecificity and linking sexes in taxonomic work on the genus.

The specimens behind the new species were collected using sweep nets, Malaise traps, and yellow pan traps, and all were preserved in absolute ethanol immediately after collection. Specimen accession codes follow a standardized prefix system in which “XZMT-” denotes specimens collected from Medog (Motuo), Xizang, and “MXZ-” abbreviates Malaise trap collections from Xizang. For morphological imaging, specimens were air-dried and stabilized with molding clay, then photographed with a Leica M205A stereomicroscope equipped with a Leica DFC-500 digital camera; image stacking was processed with Leica Application Suite software and final plates edited in Adobe Photoshop. Male genitalia were dissected after macerating the apical metasomal segments in 35% hydrogen peroxide in a boiling water bath for five minutes, and stored in glycerin. All linear measurements are given in micrometers, except body length excluding antennae, which is given in millimeters.

Conostigmus vitreus, whose name is a Latin masculine adjective meaning “glassy” or “transparent,” refers to the small, vitreous male genitalia that distinguish the species. The holotype is a male collected in Damu Township, Medog County, Nyingchi City, at 1,814 meters elevation in May 2017, with paratypes from the same locality. Males measure 1.1 to 1.5 millimeters in body length and are mostly black, with a light brown scape, dark brown pedicel, black flagellomeres, silvery ocelli and compound eyes, and light brown legs. The head is approximately 1.3 times as wide as the mesosoma, with the ocular ocellar length longer than the posterior ocellar length and an ocellar triangle with a narrow base. The mesosoma is slender, 1.5 times as long as wide, densely pubescent with granular surface sculpture, and bears a complete notaulus and a median mesoscutal sulcus whose posterior ends adjoin the transscutal articulation.

Several features of C. vitreus stand out in detail. The fore wing is 1.1 to 1.4 millimeters long, well developed and hyaline with weak dark pigmentation, with a nearly triangular pterostigma 2.4 times as long as wide and a radius weakly curved medially, 1.5 times as long as the pterostigma. The metasoma is twice as long as wide, and the smooth syntergum, which is longer than wide, carries three distinct gastral carinae approximately 0.4 times as long as the syntergum, along with a transverse, irregularly cylindrical syntergal translucent patch. The male genitalia are small, measuring 125 by 70 micrometers, and highly translucent, with a harpe shorter than the gonostipes that bears numerous slender, distally oriented apical setae; the parossiculi are not medially fused and the gonostipes are not fused with the parossiculi. The female paratype, at 1.2 millimeters, differs from the male in having a blackish-brown metasoma and orange-yellow scape, pedicel, and first four flagellomeres, and a long antennal pedicel slightly longer than flagellomeres one through eight. The species is similar to Conostigmus jilongensis but can be distinguished by its small, highly translucent male genitalia, in contrast to the large, sclerotized, brown genitalia of that species.

The second new species, Conostigmus obsidianus, takes its name from a Latin masculine adjective meaning “obsidian-like,” in reference to its entirely pitch-black body coloration. The holotype is a male collected in Gyirong County at 3,354 meters elevation in July 2023, with two female paratypes from the same locality. The male measures 1.8 millimeters in body length, and the body is uniformly black, including the head, mesosoma, metasoma, antennae, and legs, with only the wings hyaline and translucent; the compound eyes are black, smooth, and glossy, and the pterostigma is dark brown. The head is as wide as the mesosoma, with the ocular ocellar length longer than the posterior ocellar length, and notably the facial pit is absent, a character that separates this species from C. vitreus in the updated identification key. The mesosoma is slender and depressed, 1.5 times as long as wide, with a mesoscutum 1.9 times as wide as long that is finely reticulate-punctate and sparsely covered with long, curved, posteriorly directed setae.

Further distinguishing details of C. obsidianus include antennae in which the scape is distinctly longer than the teardrop-shaped pedicel, with the first flagellomere the longest and a marked length gradient in which flagellomeres shorten from the first to the fifth and then lengthen to the ninth. The fore wing is 1.4 millimeters long, narrow-elongate, and hyaline with weak dark pigmentation, with a nearly triangular pterostigma 2.3 times as long as wide. The metasoma is 1.7 times as long as wide, with a smooth syntergum longer than wide bearing three distinct gastral carinae. The male genitalia are symmetrical, elongate-elliptical, large, and strongly sclerotized and dark brown, with a harpe that is broad basally and tapers to an acute, leaf-like apex bearing four to six elongate apical setae, and a short aedeagus concealed within the harpe with only its apex exposed. The species resembles Conostigmus asperatus but differs in its uniformly pitch-black body, head as wide as the mesosoma, syntergum longer than wide, and large, dark brown, strongly sclerotized male genitalia with a leaf-like harpe apex.

The molecular work reinforced the morphological conclusions. Three COI sequences were newly generated: two representative sequences of C. vitreus and one of C. obsidianus. Three specimens of each new species were subjected to DNA barcoding, yielding two valid sequences for C. vitreus and one for C. obsidianus. The intraspecific genetic distance of C. vitreus was zero percent, supporting congruence between molecular species delimitation and morphological taxonomy, while interspecific genetic distances among the sampled Megaspilidae ranged from 11.1 to 25.7 percent. In the maximum likelihood phylogeny, built from ten COI sequences representing nine species with two Aphanogmus species as outgroups, all species were recovered as well-supported monophyletic lineages. The two individuals of C. vitreus, one female and one male, clustered together with 90 percent bootstrap support, confirming their conspecificity and providing molecular evidence for the reliable association of males and females of this species, a notable result given the sexual dimorphism that complicates such associations in the genus. Conostigmus itself formed a strongly supported monophyletic group with 84 percent bootstrap support, and both new species were placed within it, each forming distinct clades.

The study also provides an updated key to the species of Conostigmus from China, incorporating the two new taxa among the previously described species. In that key, C. obsidianus is separated from C. asperatus by the shape of the syntergum, longer rather than wider than long, while C. vitreus is distinguished from C. jilongensis by the total length of the male genitalia, less than 130 micrometers and highly translucent and hyaline in appearance, versus at least 130 micrometers and brownish and sclerotized. The authors note that the work expands the known diversity of Chinese Conostigmus and contributes additional new taxa to the fauna of the genus in Xizang, further enriching knowledge of the Himalayan Megaspilidae fauna, and that the new COI sequences provide molecular resources for future phylogenetic and biogeographic analyses of Megaspilidae. Both new species are so far known only from China’s Xizang Autonomous Region, and the specimens are deposited at Anhui Normal University as vouchers for future study.

Subject of Research: Taxonomic description of two new Conostigmus parasitoid wasp species from Xizang, China, with COI DNA barcoding and phylogenetic analysis.

Article Title: Two new species of Conostigmus Dahlbom, 1858 ( Hymenoptera , Megaspilidae ) from Xizang Autonomous Region, China

Article References: Liu, Y.-F., Zhao, W.-J., Yang, X., Li, L.-K., Huang, Y.-X., & Wang, X. (2026). Two new species of Conostigmus Dahlbom, 1858 (Hymenoptera, Megaspilidae) from Xizang Autonomous Region, China. ZooKeys, 1287, 321-334. https://doi.org/10.3897/zookeys.1287.200178

Image Credits: AI Generated

DOI: 10.3897/zookeys.1287.200178

Keywords: Conostigmus, Megaspilidae, parasitoid wasps, new species, Xizang, China, DNA barcoding, COI, taxonomy, Himalayan fauna, phylogenetics, Hymenoptera