Triartiger caiyujiei Yin & Niu 2025, sp. nov.
Creators: name: Yin, Zi-Wei
name: Niu, Xiao-Ling
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Triartiger
Triartiger caiyujiei

description: Triartiger caiyujiei Yin & Niu sp. nov.
Figs 1, 2
Type material.
Holotype: China: • ♂, ‘ China: Zhejiang, Linan City, W. Tianmushan Nature Reserve, 30°20'33.22"N, 119°25'41.19"E, pass to summit, nr. Luopansong, 1245 m elev., 03. v. 2024, C.-Y. Jie leg., 天目山近罗盘松石块下蚁巢, 蔡余杰’ (SNUC).
Diagnosis.
Male. Habitus moderately stout, with relatively long antennae and legs. Body length approximately 2.3 mm. Head and pronotal base with distinct microsculpture cuticle and covered by suberect setae; antenna with short antennomeres 1 and 2 and exceptionally long antennomere 3; 3 approximately 13 × as long as 2. Elytra finely punctate, lacking linear sculpture, posterior margins with large trichomes. Mesofemur with large blade-like ventral spine, mesotibia with large triangular spine at approximately middle of mesal margin; metafemur simple. Abdomen suboval; composite tergite deeply and broadly concave at base, with pair of broad basolateral trichomes, disc glabrous and with long, sparse setae; paratergites 1 (IV) with broadly curved longitudinal trichomes at bases; posterior margin of composite tergite and tergite 4 (VII) with row of long setae. Aedeagus dorso-ventrally symmetrical, divided into basal and apical parts; basal capsule with large ventral projection, apical lobe abruptly narrowed before apex. Female. Unknown.
Description.
Male. Body (Fig. 1 A) length 2.33 mm; colour reddish-brown, tarsi and mouthparts lighter in colour. Dorsal surface of head, pronotum and elytral disc covered with suberect setae, those of head and pronotum distinctly longer than elytral disc; setae of abdominal disc sparse and long, those along posterior margin much denser than disc.
Head (Figs 1 B and C) dorsally subcylindrical, much longer than wide, length 0.46 mm, width across eyes 0.30 mm; vertex slightly convex, foveae (dorsal tentorial pits) (Fig. 1 B; vf) laterally located just above eyes; frons forming narrow rostrum, extending anteriorly to form vertical keel at middle; vertex and lateral portions of head with distinct microsculpture, frons smooth, finely punctate; clypeus markedly short, anterior margin with short, sparse setae. Venter with rough surface, gular region broadly and moderately impressed, tiny gular foveae (posterior tentorial pits) widely separated, lacking median carina. Compound eyes weakly prominent, each composed of approximately 10 ommatidia. Cervical part sub-globose, surface with distinct reticulate microsculpture. Antenna (Fig. 1 D) 0.72 mm long, lacking modifications; antennomere 1 thick and short, dorsally completely covered by rostrum, invisible, 2 slightly shorter than 1, transverse, dorsally partially visible, antennomere 3, 0.67 mm long, 0.15 mm wide, 13.4 × as long as 2, narrowing from base towards apex, broadest and truncate at apex.
Pronotum (Fig. 1 C) approximately as long as wide, length 0.44 mm, width 0.43 mm, widest at approximately anterior 1 / 3, basal 1 / 3 with microsculpture similar to that of head; lateral margins rounded at widest point, narrowing anteriorly and slightly so posteriorly; disc slightly impressed mediobasally, lacking foveae. Prosternum with basisternal (precoxal) portion longer than procoxal rests, lacking procoxal foveae; hypomera completely fused with sternum, lacking hypomeral grooves and carinae.
Elytra tightly joined, subtrapezoidal, much wider than long, length 0.49 mm, width 0.94 mm, lacking foveae, anterior margin greatly oblique; each elytron with one complete adsutural carina and one short discal carina originating from base; posterolateral margins roundly convex; posteromedial portions with patches of dense, long setae, posterolateral portions with large, triangular trichomes (Fig. 1 A). Metathoracic wings remnant.
Mesoventrite short, fused with metaventrite, with median mesoventral foveae anterior to median keel, the latter angularly projecting at middle; pair of small lateral mesoventral foveae present. Metaventrite greatly convex at middle, descending laterally, lacking foveae, broad metaventral intercoxal process widely separating coxae and broadly and slightly convex at middle; area anterior to process with golden, densely setose patch.
Legs long; mesofemur and mesotibia (Fig. 1 F) each with one large, blade-like and one much larger, subtriangular spine on ventral and middle of mesal margin, respectively; metafemur (Fig. 1 G) simple, lacking tubercles or spines.
Abdomen slightly broader than elytra, suboval, widest at basolateral margins of composite tergite, length 0.92 mm, width 0.98 mm. Tergite 1 (composite tergite formed by tergites 1–3 (IV – VI)) deeply concave at base, with pair of large basolateral sockets, with large trichomes (Fig. 1 E) mesal and posterior to sockets, 2 (VII) short, transverse, with pair of small lateral nodules and foveae, 3 (VIII) transverse, roundly triangular, with pair of small basolateral foveae, posterior margin rounded. Paratergites 1 (IV) with greatly curved, longitudinal trichomes (Fig. 1 E) at bases. Sternites finely punctate, 2 (IV) as long as 3 (V) – 5 (VII) combined, with band of dense setae along base, with slightly prominent keel at middle, area lateral to keel weakly impressed, lacking foveae, 3 at middle as long as 4 (VI) and 5 combined, 2–4 each with distinct microsculpture on posterior half; 6 (VIII) transverse, posterior margin broadly emarginate at middle, 7 (IX) not observed.
Aedeagus (Figs 1 H – J) 0.47 mm long, dorsoventrally symmetrical; median lobe divided into basal capsule and apical lobe, lacking parameres; basal capsule elongate, broadened and rounded at base, with large ventral projection and small, transverse foramen, dorsally with large oval diaphragm, apical lobe narrowing apically and abruptly narrowed before apex, in lateral view pointed apically, with two short, tiny apical setae; endophallus armature composed of short sclerite at middle of capsule.
Female. Unknown.
Comparative notes.
The addition of the present species brings the total number of known species of the genus to seven. This species is relatively large within the genus and can be readily distinguished from T. reductus Nomura, T. jiangxinongda Yin & Du and T. spatulatus Yin by its exceptionally elongate terminal antennal segment, whereas the latter three species possess considerably shorter antennae in proportion to their head size. The new species can be easily differentiated from T. urceus Kubota and T. nomurai Besuchet by the nearly straight mesal and lateral margins of antennomere 3, in contrast to the slightly swollen mesal margins in the latter two species. Triartiger caiyujiei sp. nov. differs from T. klapperichorum Nomura in its relatively longer antennomere 3 (13 × vs. 8.5 × as long as antennomere 2) and the presence of additional setose patches on the posteromedial portions of the elytra. To facilitate identification, an updated key to all known species is provided below.
Distribution.
East China: Zhejiang (Fig. 2 A).
Biology.
The single adult was collected from a small Pseudolasius Emery ant colony nesting under a stone (Fig. 2 B) in a mixed coniferous-deciduous forest (Fig. 2 C). This represents only the third Triartiger species with a known symbiotic host (Fig. 2 D, E). Members of this genus are notably rare in both the field and museum collections and the biology and natural history of most species remain poorly understood. The current knowledge on the distribution, collecting methods, host associations and material availability of the genus is summarised in Table 1 to facilitate future studies.
* Note: FIT = flight intercept trap.
Etymology.
The species epithet is dedicated to Yu-Jie Cai (蔡余杰), who collected the single adult and provided it for study. The name is a noun in the genitive case.
description: Published as part of Yin, Zi-Wei & Niu, Xiao-Ling, 2025, Triartiger caiyujiei sp. nov., a remarkable clavigerite beetle (Coleoptera, Staphylinidae, Pselaphinae) associated with Pseudolasius ants (Hymenoptera, Formicidae) from East China, pp. 9-14 in Deutsche Entomologische Zeitschrift 72 (1) on pages 9-14, DOI: 10.3897/dez.72.144365