Trichacis tristis
Creators: name: Awad, Jessica
name: Krogmann, Lars
name: Talamas, Elijah
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Platygastridae
Trichacis
Trichacis tristis

description: Trichacis tristis (Nees, 1834)
(Figs 1A, B, E; 2A, B; 3; 4A–H; 5E–G)
Platygaster tristis Nees, 1834: 302, 303 (neotype NHMW).
Platygaster didas Walker, 1835: 240 (lectotype NMINH). Syn. nov.
Platygaster pisis Walker, 1835: 239 (lectotype NMINH). Syn. nov.
Platygaster remulus Walker, 1835: 239, 240 (lectotype NMINH). Syn. nov.
Trichacis didas (Walker, 1835). Förster 1856: 115 (generic transfer).
Trichacis pisis (Walker, 1835). Förster 1856: 115 (generic transfer).
Trichacis remulus (Walker, 1835). Förster 1856: 115 (generic transfer).
Trichacis tristis (Nees, 1834). Dalla Torre 1898: 480 (generic transfer).
Trichacis abdominalis Thomson, 1859: 79 (holotype NHRS, missing from pin). Syn. nov.
Trichacis opaca Thomson, 1859: 78, 79 (lectotype MZLU). Buhl & Notton 2009: 1700 (jr. syn. of T. pisis).
Trichacis illusor Kieffer, 1916: 564. Syn. nov.
Trichacis illusor fusca Kieffer, 1916: 565.
Trichacis illusor illusor Kieffer, 1926: 713, 714, Fig 294.
Trichacis pulchricornis Szelényi, 1953: 484, 485. Syn. nov.
Trichacis bidentiscutum Szabó, 1981: 289, 290. Syn. nov.
Trichacis fusciala Szabó, 1981: 289. Syn. nov.
Trichacis hajduica Szabó, 1981: 288. Syn. nov.
Trichacis quadriclava Szabó, 1981: 290. Syn. nov.
Trichacis nosferatus Buhl, 1997: 97, Figs 13–16 (holotype ZMUN). Syn. nov.
Trichacis vitreus Buhl, 1997: 96, Figs 9–12 (holotype NHMD). Syn. nov.
Trichacis weiperti Buhl, 2019: 344, 345, Figs 9, 10 (holotype NME). Syn. nov.
Trichacis persicus Asadi & Buhl, 2021: 333–335, Fig. 1 (holotype HMIM). Syn. nov.
Description. Body length: 1.5–2.1 mm (n=10). Body color: dark brown to black. Antenna color: light brown to dark brown. Mandible color: light brown to dark brown. Leg color: yellow to dark brown. Coxa color: dark brown to black. Wing color: pale with brown markings basally, sometimes entirely pale. Head. Head shape: ovoid, slightly transverse. Sculpture of ocellar triangle: coriaceous. OOL:LOL: 1, or OOL slightly shorter than LOL. Mandibular sculpture: proximally striate. Mandibles: clasp-like, teeth equal in size. Sculpture of frons: smooth to coriaceous, sometimes with central keel indicated by a faint line. Number of epitorular striae: 5−7. Interantennal process: truncate. Clypeus: exposed, medial carina present below interantennal process. Ventral clypeal margin: straight. Number of clypeal setae: 8. Sculpture of gena: smooth along compound eye, sometimes faintly striate posteriorly; Hyperoccipital carina: present medially, attenuating laterally. Sculpture of vertex anterior to hyperoccipital carina: coriaceous to striate. Vertex posterior to hyperoccipital carina: slightly impressed medially, with whorled or striate sculpture. Occipital carina: incomplete, not extending ventrally to posterior articulation of the mandible. Setation of occiput: dense in ventral half. Projection on temples: absent. Distance between LO and HOC: 2 ocellar diameters.
Female antenna. A1 length: not surpassing vertex of head. Number of clavomeres: 4. Claval formula: 1-1-1-1. Male antenna. A1 length: not surpassing vertex of head. A2–A5: cylindrical, A3 and A4 semi-appressed. Male sex segment (A4): not expanded, ventral portion flattened with minute longitudinal striae. A6–A10: cylindrical, setose, A10 longest. Mesosoma. Mesoscutum in lateral view: moderately arched. Antero-admedian line: present, faint. Notaulus: present, complete or nearly so. Sculpture of mesoscutum: reticulate-coriaceous, sometimes with smooth patches posteriorly. Setation of mesoscutum: moderate to dense, evenly or unevenly distributed. Parapsidal signum: indicated by a faint line. Cervical pronotal area: anteriorly smooth and glabrous.Shape of mesoscutum in lateral view: slightly flattened. Mesoscutellar setal patch: round to triangular, located in posterior half. Sculpture of mesopleuron: smooth, sometimes with very faint striae in dorsal half. Mesopleural carina: present anteriorly, incomplete. Fore wing length: surpassing metasoma. Fore wing marginal setae: very short, slightly longer on posterior distal margin. Female metasoma. Metasoma length: approximately as long as head and mesosoma combined. Setation of pits on anterior T2 present. Shape of T1: transverse. Sculpture of T1: medially striate, lateral aspect obscured by dense setation. Sculpture of T2: smooth with a few striae between anterior pits. Sculpture of T3–T6: finely punctate. Felt fields: short, densely to sparsely setose. Sculpture of S2: smooth or finely punctate. Male metasoma. Metasoma length: slightly shorter than head and mesosoma combined, otherwise similar to female.
Diagnosis. Trichacis tristis (Figs 2A, B; 3) does not have any autapomorphic structures to easily distinguish it among the world fauna. The relatively extensive setation and sculpturing of the posterior vertex and mesoscutum (Fig. 3B, E) set it apart from many species in the Western Hemisphere, but a thorough diagnosis must rely on a combination of characters. The following diagnosis uses characters from the keys of Masner (1983) and Arias-Penna et al. (2012): temples unarmed; mandibles clasped; clypeus with 8 setae; interantennal process truncate; scape not surpassing vertex; posterior vertex with whorled or striate sculpture medially; hyperoccipital carina laterally weakened, surpassing line of inner eye margin and not merging with striae; internotaular area sculptured at least anteriorly, moderately to densely setose; mesopleural carina incomplete; mesoscutellar setal patch round to triangular; fore wing usually with brown markings in proximal third (may be faint or faded), surpassing apex of metasoma in females.
Trichacis tristis is most similar to T. virginiensis Ashmead, 1893 and T. celticola Masner, 1983 in the Nearctic region. Trichacis virginiensis can be separated by the hooked interantennal process, which is simple in T. tristis, and by the strongly transverse head, which is only slightly transverse in T. tristis. Trichacis celticola has short fore wings, not surpassing the apex of the female metasoma, whereas the fore wings in female T. tristis extend well beyond the metasoma.
Distribution. Trichacis tristis is widespread in the Palearctic, ranging from Ireland to Japan, north to Scandinavia and south to the Mediterranean Sea.
Biological associations. Trichacis tristis is associated with Mayetiola destructor (Say, 1817) and M. avenae (Marchal, 1895), both of which are herbivorous on grain crops and wild grasses (Poaceae). Embryonic and larval development of T. tristis (as T. remulus) were described and illustrated by Marchal (1906).
Type material examined. Neotype of Platygaster tristis ♀, GERMANY, original exemplar, NHMW-HYM-0005319 (NHMW). Lectotype of P. didas ♁, UNITED KINGDOM, London, NMINH_2018_11_18; lectotype of P. pisis ♁, London, NMINH _2018_11_24; lectotype of P. remulus ♁, London, NMINH _2018_11_25 (NMINH). Lectotype of T. opaca ♀, SWEDEN, Ringsjön, June, 2856:1-2 (MZLU). Holotype of T. nosferatus ♀, NORWAY, Tofteholmen, 7–31 July 1991, L.O. Hansen (ZMUN). Holotype of T. vitreus ♀, GREECE, Peloponnese, 5km S Monemvasia, 27 November 1983, G. Christensen, ZMUC 00021950 (NHMD). Holotype of T. weiperti ♀, GERMANY, Thuringia, Kyffhäuser, Steinthaleben, mixed oak forest, 230m, 26 June 1998, J. Weipert (NME).
Additional material examined. 1 specimen, AFGHANISTAN, Kabul, 9–11 April 1974, J. Papp; 1 specimen, ARMENIA, Tsakhador, 2000 m, 4 June 1980, J. Papp (HNHM). 1 ♀, AUSTRIA, Piesting, C. Tschek (NHMW). 1 ♁, BULGARIA, Kneja, reared from flies on wheat stalks, December 1960, Samfirov; 1 ♁, CROATIA, Laz, 10 June 1974, J. Papp (HNHM). 1 ♁, FRANCE, Meuse, Dompcevrin, 3–4 June 1985, M.J. Gliswit; 1 specimen, Bitche, 21 June 1989, H. Vlug (HVC). 1 ♁, 4 ♀, GERMANY, North Rhine-Westphalia, Nationalpark Eifel, Helingsberg, May–June 2009, J. Esser, SMNS _Hym_Pla_ 000720, 721, 724, 726, 727; 1 ♁, Baden-Württemberg, Rems-Murr-Kreis, Aspach bei Backnang, forest, 15–30 April 2013, Krogmann et al., SMNS _Hym_Pla_ 000729; 1 ♁, 5 ♀, Mecklenburg-Vorpommern, Rügen Island, Kniepow, 17–23 May 2015, F. Koch, SMNS _Hym_Pla_ 796– 798, 804–806 (SMNS). 1 ♀, GREECE, Macedonia and Thrace Decentralized Administration, Macedonia Central Periphery, Kerkini Lake, 41.2258°N, 23.0845°E, 45m, March–April 2007, G. Ramel, OSUC 413928 (OSUC). 2 ♁, 2 ♀, HUNGARY, Ujszentmargita, 7 May 1975, J. Papp; 2 ♁, 3 ♀, Ujszentmargita, 21–25 April 1975, Hamorine & Marotine; 1 ♁, 1 ♀, Hortobagy, Zam, 16–18 June 1975, Kaszab & Mahunka; 7 ♀, Pécs, 6 May 1955, J.B. Szabó; 2 ♁, Tompa, 12 April 1960, Erdös (HNHM). 1 ♀, IRELAND, Glen of the Downs on Wicklow, 12 July 1983, H. Vlug; 1♀, ITALY, Fusine near Tarvisio, 11 August 1948, H. Vlug (HVC); 1 ♀, E. Graeffe, NHMW-HY ♁0006911 (NHMW). 1 specimen, MONGOLIA, Central Aimak, Ulaanbaatar, Bogd Khan, 1650–1950m, 4 June 1966, Kaszab; 1 ♀, ROMANIA, Transylvania, Homoródkeményfalva, 8 May 1995, I. Rozner (HNHM). 1 ♁, 1 ♀, SWEDEN, Småland, Kronoberg, 4km N Hinnyerd, 56.6497°N, 13.5869°E, 7 July 1994, M. Söderlund, OSUC 45132, 45134 (OSUC). 3 ♀, UNITED KINGDOM, London, NHM Wildlife Garden, meadow, N51°29’45.6” W0°10’42.1 ”, April–May 2013, Sivell et al. (NHMUK).
Remarks on intraspecific variation. European authors described T. tristis at least 15 times from England, Germany, Greece, Hungary, Iran, Italy, Sweden, and Norway (Figs 4A–H).This state of affairs is partially attributable to intraspecific variation, separation based on minute differences, and examination of small series. For example, T. weiperti (Fig. 4H) was treated as new based on antennomere measurements from a single specimen. Viewing angle can greatly influence measurement. Figures 1 A−B illustrate the antenna of the same specimen at different angles, demonstrating the drastic difference. Antennomere measurements should only be taken in lateral view, preferably from antennae that have been removed from the head and mounted on a microscope slide. Antennomeres are also subject to allometric scaling and host-related variation (Johnson et al. 1987). Coloration is similarly unreliable and can vary with host species (Talamas et al. 2021), geographic region (Vlug 1985), or preservation history (Banks 1909). Buhl (1997) diagnosed T. vitreus (Fig. 4F) by its pale wings and legs, which likely faded in color during the 14 years between its collection and description. We have found no support for the description of species based solely on minor differences in coloration or antennomere size.
Cuticular sculpture is more useful for diagnosis, although this character is somewhat variable in T. tristis. The frons sometimes exhibits a longitudinal line or thin furrow ventral to the median ocellus as described in T. pulchricornis (Fig. 1E), and the mesopleuron sometimes exhibits very faint striations as described in T. nosferatus (Fig 3E, 4G). However, the mesopleural sculpture of T. tristis is always very smooth in comparison to the conspicuous striation found in T. striata Masner, 1983 (Fig. 4I). It should also be noted that description of new species from singleton specimens in poor condition, such as the holotype of T. nosferatus (Fig. 4G) is a poor choice, as it creates a challenge to observing characters of interest.
Remarks on additional synonymies. The Walker species of Trichacis (T. didas, T. pisis, and T. remulus) (Fig. 4C–E) were redescribed, illustrated, and keyed by Vlug (1985). He suspected that they were conspecific, with very slight variation in color and antennomere shape, but cautiously declined to take taxonomic action without examining more material. Similarly, Arnold Förster noted that he thought T. didas, T. pisis, and T. remulus were conspecific with T. tristis, based on original exemplars of these species received from their respective authors (unpublished label data, NHMW). Our morphological assessment of the types confirms the suspicions of both Vlug and Förster.
We did not locate the types of T. abdominalis Thomson, 1859 (Ringsjön, Sweden) and T. illusor Kieffer, 1916 (Trieste, Italy). However, the descriptions and geographic localities for both species match the morphology and distribution of T. tristis.
Trichacis persicus was described as being similar to T. tristis, but with minor differences in the proportions of the antennomeres. This diagnosis, the photographs provided in the description, and the locality (a wheat-producing region with agricultural fields visible in satellite photos), led us to conclude that T. persicus is a junior synonym of T. tristis.
Remarks on the Hungarian species of Trichacis. Gusztáv Szelényi worked as a plant protection entomologist in Hungary in the early to mid-20th century. His agricultural research led him to parasitoid taxonomy, including a few descriptions of Platygastridae, one of which was T. pulchricornis Szelényi, 1953. The type of this species was not found in HNHM. However, other material from the type locality, Bátorliget, included no Trichacis species besides the common T. tristis. The description of T. pulchricornis is also consistent with our concept of T. tristis.
János Barna Szabó was a prolific self-taught hymenopterist in Hungary in the mid-20th century. His knowledge of Platygastroidea came primarily from one book: Das Tierreich volume 48 by Jean-Jacques Kieffer (1926) (Zoltán Vas, pers. comm.). The resulting taxonomic work therefore had limited perspective. It is clear from examination of Szabó’s platygastrid collection that his generic concepts were sometimes inaccurate. Szabó described eight species of Trichacis, four of which were published in 1977 (T. afurcata, T. hungarica, T. pannonica, and T. tatika). The holotypes of these specimens, along with some other material determined by Szabó as Trichacis, belong to the genus Amblyaspis (Figs 5A–D), into which we now transfer them. It is likely that these are junior synonyms as well, but the chaotic state of species-level taxonomy in Amblyaspis does not allow for more specific determination at present.
Based on determination labels in HNHM, it appears that Szabó adopted the prevailing concept of Trichacis sometime after 1977. He published four species of Trichacis from Hortobagy National Park in 1981 (T. bidentiscutum, T. fusciala, T. hajduica, and T. quadriclava). These holotypes were not found in HNHM. However, examination of extensive material from the original collecting events yielded no evidence of any Trichacis species other than T. tristis, which was present in abundance (Figs 5E–G).
Furthermore, thorough examination of the platygastrid holdings at HNHM indicates that the Trichacis fauna of Hungary, like the rest of central Europe, includes only one species. We conclude that T. pulchricornis, T. bidentiscutum, T. fusciala, T. hajduica, and T. quadriclava are best treated as junior synonyms of T. tristis.
description: Published as part of Awad, Jessica, Krogmann, Lars & Talamas, Elijah, 2023, Illuminating a Dark Taxon: Revision of European Trichacis Förster (Hymenoptera Platygastridae) reveals a glut of synonyms, pp. 563-577 in Zootaxa 5278 (3) on pages 565-572, DOI: 10.11646/zootaxa.5278.3.8, http://zenodo.org/record/7906722