Aphanogmus kretschmanni Moser, 2023

Moser, Marina, Ulmer, Jonah M., Kamp, Thomas Van De, Vasilița, Cristina, Renninger, Maura, Mikó, István & Krogmann, Lars, 2023, Surprising morphological diversity in ceraphronid wasps revealed by a distinctive new species of Aphanogmus (Hymenoptera: Ceraphronoidea), European Journal of Taxonomy 864 (1), pp. 146-166 : 150-159

Aphanogmus kretschmanni Moser sp. nov.

urn:lsid:zoobank.org:act:8848B3FB-DC1D-465C-9E67-284EE86BB4CA

Figs 1–3

Diagnosis (female)

The female has seven conspicuous spines in two rows along the ventral edge of the 7 th metasomal sternite, with two spines next to each other in the 1st and 5th position.

Etymology

The specific name is a patronym for Winfried Kretschmann, the current Minister-President of the state of Baden-Württemberg ( Germany), to honour his scientific curiosity and commitment to preserving biodiversity in his political environment.

Type material

Holotype

GERMANY • ♀ (the holotype is missing the right fore- and mid-tarsus); Baden-Württemberg, Tübingen, Hirschau, Riedweingärten , plot number 4400; 48.504817° N, 8.985067° E; 375 m a.s.l.; 29 Aug.–12 Sep. 2014; Kothe T., Engelhardt M., Bartsch D. leg.; Malaise trap; SMNS SMNS_Hym_Cer_000227 .

The 3D model of the holotype, which serves as a cybertype, as well as the original CT image series are available online through MorphoSource (CT image series: https://doi.org/10.17602/M2/ M449721; full habitus mesh: https://doi.org/10.17602/M2/M449724; post-edited full habitus mesh https://doi.org/10.17602/M2/M449727).

Paratypes

GERMANY • 1 ♀ (in immaculate condition); Baden-Württemberg, Enzkreis, Königsbach-Stein, NSG 2.119 Beim Steiner Mittelberg ; 48.970371° N, 8.659000° E; 181 m a.s.l.; 22 May–5 Jun. 2019; Entomologischer Verein Krefeld e. V. 1905 leg.; Malaise trap; SMNS SMNS_Hym_Hym_027509 • 1 ♀ (in immaculate condition); Baden-Württemberg, Tübingen, Hirschau, Oberes Tal , plot number 4244; 48.505033° N, 8.993467° E; 368 m a.s.l.; 17–31 Jul. 2014; Kothe T., Engelhardt M., Bartsch D. leg.; Malaise trap; ZFMK SMNS_Hym_Cer_000647 • 1 ♀ (in immaculate condition); Baden-Württemberg, Tübingen, Hirschau, Oberes Tal , plot number 4244; 48.505033° N, 8.993467° E; 368 m a.s.l.; 29 Aug.–12 Sep. 2014; Kothe T., Engelhardt M., Bartsch D. leg.; Malaise trap; ZSM SMNS_Hym_Cer_000648 .

Additional material examined

GERMANY • 1 ♀; same collection data as for holotype; 6–20 Jun. 2014; SMNS SMNS_Hym_Cer_000408 • 1 ♀; Baden-Württemberg, Tübingen, Hirschau, Oberes Tal , plot number 4244; 48.505033° N, 8.993467° E; 368 m a.s.l.; 17–31 Jul. 2014; Kothe T., Engelhardt M., Bartsch D. leg.; Malaise trap; SMNS SMNS_Hym_Cer_000425 • 1 ♀; same collection data as for preceding; BOLD Sample ID: SMNS_1179430; GenBank: OP722468 ; SMNS SMNS_Hym_Cer_000467 • 1 ♀; same collection data as for preceding; BOLD Sample ID: SMNS_1179432; GenBank: OP722465 ; SMNS SMNS_ Hym_Cer_000468 • 1 ♀; same collection data as for preceding; BOLD Sample ID: SMNS_1179434, GenBank: OP722466 ; SMNS SMNS_Hym_Cer_000470 • 1 ♀; same collection data as for preceding; BOLD Sample ID: SMNS_1179433; GenBank: OP722464 ; UNHP SMNS_Hym_Cer_000469 • 1 ♀; same collection data as for preceding; UNHP SMNS_Hym_Cer_000488 • 2 ♀; same collection data as for preceding; 29 Aug.–12 Sep. 2014; SMNS SMNS_Hym_Cer_000440 • 1 ♀; same collection data as for preceding; SMNS SMNS_Hym_Cer_000464 • 1 ♀; same collection data as for preceding; BOLD Sample ID: SMNS_1179428; GenBank: OP722469 ; SMNS SMNS_Hym_Cer_000465 • 1 ♀; same collection data as for preceding; BOLD Sample ID: SMNS_1179429; GenBank: OP722462 ; SMNS SMNS_Hym_Cer_000466 • 1 ♀; same collection data as for preceding; 12–26 Sep. 2014; BOLD Sample ID: SMNS_1177257; GenBank: OP722467 ; SMNS SMNS_Hym_Cer_000445 • 1 ♀; same collection data as for preceding; SMNS SMNS_Hym_Cer_000446 • 1 ♀; same collection data as for preceding; 26 Sep.–9 Oct. 2014; BOLD Sample ID: SMNS_1177266; GenBank: OP722463 ; SMNS SMNS_Hym_Cer_000451 • 1 ♀; Baden-Württemberg, Karlsruhe, Östringen, NSG 2.217 Apfelberg , plot number 9836; 49.167541° N, 8.790300° E; 181 m a.s.l.; 16–30 Jul. 2019; Entomologischer Verein Krefeld e. V. 1905 leg.; Malaise trap; SMNS SMNS_Hym_Cer_000543 • 1 ♀; same collection data as for preceding; 27 Aug.–10 Sep. 2019; SMNS SMNS_Hym_Hym_027357 • 1 ♀; same collection data as for preceding; 10–24 Sep. 2019; SMNS SMNS_Hym_Cer_000571 • 1 ♀; same collection data as for preceding; 24 Sep.–8 Oct. 2019; SMNS SMNS_Hym_Cer_000544 • 2 ♀♀; same collection data as for preceding; 8–22 Oct. 2019; SMNS SMNS_Hym_Hym_027358 . • 1 ♀; same collection data as for preceding; SMNS SMNS_Hym_Cer_000649 • 4 ♀; Baden-Württemberg, Enzkreis, Königsbach-Stein, NSG 2.119 Beim Steiner Mittelberg ; 48.970371° N, 8.659000° E; 181 m a.s.l.; 3–17 Jul. 2019; Entomologischer Verein Krefeld e. V. 1905 leg.; Malaise trap; SMNS SMNS_Hym_Hym_027558 . • 2 ♀♀; same collection data as for preceding; 17–31 Jul. 2019; SMNS SMNS_Hym_Hym_027726 . • 1 ♀; same collection data as for preceding; 28 Aug.–11 Sep. 2019; SMNS SMNS_Hym_Hym_027685 .

For detailed description of localities, habitats and further material see Supp. file 3.

Description

COLOURATION. Head dark brown, almost black. Mesosoma dorsally concolourous with head, ventrally dark chestnut brown. Metasoma lighter brown. Scape, distal end of pedicel and tibiae light amber brown, tarsi pale ochre, flagellar segments brown, concolourous with femora, distal flagellar segments slightly darker. Wings entirely hyaline. Wing venation light brown, marginal vein darker, light brown stigmal vein with dark margin.

MEASUREMENTS. Total body length is 0.7–1.1 mm (holotype: 1 mm).

HEAD. Entire head with imbricate sculpture. Face, frons and eyes covered in short whitish pubescence. Oval in frontal view, 1.1–1.4 (1.3) times as broad as high. Head hypognathous. Truncated in lateral view with preoccipital carina delimiting sharply the deeply concave preoccipital lunula. Preoccipital carina medially interrupted by preoccipital furrow, which fades anteriorly ending inside the ocellar triangle posterior to the median ocellus. Preoccipital furrow as wide anteriorly as posteriorly and crenulate along its entire length. Crenulate occipital carina with continuous median flange. Eyes large, 0.6–0.7 (0.7) times as high as head. Ocellar triangle obtuse, POL:LOL: 1.25; OOL:POL: 0.8. Postocellar carina absent. Preocellar pit present. Anterior ocellar fovea extended ventrally into short facial sulcus reaching dorsal margin of frontal depression.Antennal scrobe present, ventrally delimited by intertorular carina. Clypeus convex and rectangular (1.5 times as broad as high). Supraclypeal depression, subtorular carina, carina delimiting antennal scrobe, frontal ledge and subantennal groove absent. Mandibles with two distinct teeth, without mandibular lancea. Mandible slender, length along ventral edge 3.3 times as long as height of mandible measured in the middle of its length. Maxillae with four palpomeres.

ANTENNAE. Antennae with eight flagellar segments. Scape distally with flagellar scrobe. Scape 2.1–3.1 (2.5) times as long as pedicel. Pedicel 1.2 times as long as F1. Scape as long as pedicel, F1 and F2 combined. F1 significantly longer than any segments F2–F7 but shorter than F8; F2 to F7 of similar length. F8 significantly longer than other flagellar segments, longer than F6 and F7 combined. Maximum width of scape 1.6 times maximum width of pedicel. Width of flagellar segments F1–F8 increasing steadily, F8 almost as broad as scape. F1 cylindrical, twice as long as broad; F2 subquadrate, 1.3 times longer than broad; F3–F7 subquadrate; F8 cylindrical, twice as long as broad.

MESOSOMA. Mesoscutum, mesoscutellar-axillar complex, pronotum and anterior mesopleural area with imbricate sculpture of flat scutes, lower half of mesometapleuron smooth, upper half with roughly strigate sculpture arising anteriorly from the anterior mesopleural sulcus and the mesometapleural sulcus. Mesoscutum and mesoscutellum with numerous short pale setae, axillular carina hemmed with one row of white axillular setae. Mesosoma laterally compressed, 1.2–1.8 (1.6) times as long as broad, 1.4–1.6 (1.5) times as high as broad. Mesoscutum broadest part of mesosoma, maximum mesoscutal width 2.1 times as wide as mesoscutellum. Pronotum triangular in lateral view with transverse pronotal sulcus extending halfway along pronotum. Ventral pronotal pit present. Anterior portion of mesoscutum steeply sloping in lateral view, anteriorly articulating with pronotum at an acute angle. Median mesoscutal sulcus complete and posteriorly reaching transscutal articulation, notauli absent. Mesoscutum posterolaterally delimited by pronounced parascutal carina.Axillar carina pronounced anteriorly but fading posteriorly. Interaxillar sulcus present, extending medially into scutoscutellar sulcus. Axillae distinct in dorsal view. Scutoscutellar sulcus broad and foveate, angled medially and reaching laterally the ventral margin of mesoscutellum. Circumscutellar carina sharply pronounced, lined with numerous axillular setae. Axillula very steep, almost vertical in relation to scutellar disc. Frenal area very short and separated from mesoscutellum by a steeply plunging ridge. Metanotal-propodeal sulcus foveate. Anteromedian projection of the metanoto-propodeo-metapecto-mesopectal complex simple and straight, posteriorly extending the mesonotum. Metanotal-propodeal sulcus distinctly scrobiculate. Mesometapleuron roughly triangular, higher than long in lateral view. Posterior edge of mesometapleuron extends into blunt, down-curved spine at fusion point of metapleural carina and ventral metapleural carina. Dorsal mesometapleural carina along its length slightly undulate, interrupted by propodeal spiracle, posteriorly extending into posterior propodeal projection. Ventral metapleural carina distinctly raised, continuing ventrally into raised ventral mesopleural carina and dorsally into metapleural carina.Anterior mesopleural sulcus distinct, separating anterior mesopleural area from rest of mesopleuron. Mesometapleural sulcus extending halfway across mesometapleuron, fading posteriorly. Lateral propodeal carina distinct, crossing propodeal spiracle. Posterior propodeal projections pronounced and rounded.

LEGS. Proximal articulation of metacoxa distinctly foveate. Medial side of hind tibia with dense bristles in distal half, first tarsal segment with two rows of bristles medially. Pro-, meso and metatrochanter of similar length. Femur size increasing from pro- to metafemur, mesofemur 1.1 times, metafemur 1.3 times as long as profemur. Metatibia 1.14 times as long as mesotibia and 1.47 times as long as protibia. 5 th tarsomere of hindleg 1.14 times as long as that of midleg and 1.29 times as long as that of foreleg. Tarsi of similar widths. Front and mid tarsal claws are of comparable size, hind tarsal claws slightly larger.

WINGS. Forewing very long, 0.73–0.96 mm (0.81 mm), extending distinctly beyond metasoma. Forewing broad, 1.5 times as long as broad. Marginal setae at an acute angle (34.2°) to anterior wing margin. Posterior margin of forewing remarkably straight at level of stigmal vein, slightly sclerotised and without setation proximal to straight part of the wing margin. Marginal vein with triangular elements (sensu Mikó et al. 2018). Translucent break between marginal vein and linear stigma. Stigmal vein uniformly bent, slightly increasing in width posteriorly. Anterio-proximal part of marginal vein lined with jutting setae. Hindwing slender, 4.1 times as long as broad. Posterior margin of hind wing lined with setae, setae 0.23 times as long as maximum width of hind wing, these setae significantly longer than setae on forewing. No venation, wing slightly sclerotised below hamuli. Three hamuli present. WIP of forewing indicates highest thickness of wing membrane below distal portion of the marginal vein posterior to the costal notch and lowest thickness on distal posterior wing margin. WIP of hindwing with large elliptical area of low membrane thickness along the setose distal half of the posterior wing margin.

METASOMA. Syntergum margined by transverse carina anteriorly. Syntergum with nine longitudinal striae, present only anteriorly and distributed with subequal distance over width of metasoma. Anterolateral margin of synsternum with distinct foveate carina that converges ventrally in a keel. Ventral edge of 7 th metasomal sternite with seven conspicuous spines in two rows, with two spines next to each other in the most ventral and 5 th position. Syntergum broadest tergite and slightly longer than all other tergites combined.

WATERSTON’S EVAPORATORIUM. On metasomal T6 oblong, acrotergal calyx present, distal crenulate carina on T6 present on caudal setal row, submedian patches absent, campaniform sensillae absent, tergal apodeme with sclerotised ridge along inner margin that also transverses the base of the apodeme, tergal apodemes parallel, at most slightly diverging distally, evaporatorium without basomedial constriction.

OVIPOSITOR. With a large distance between the anterior angle of the first valvifer (ang) and the intervalvifer articulation (iva). First valvifer angled at the tergo-valvifer articulation (tva), therefore appearing convex. First valvifer not subdivided. Tva situated approximately in the middle of the posterior margin of the first valvifer (1vf). Basal line of the second valvifer sharply defined. Dorsal projection of second valvifer shorter than length of anterior area of second valvifer. Anterior and posterior section of the dorsal flange of the second valvifer sharply defined. Venom gland reservoir present, surrounded by second valvifer. First valvula tapers distally in lateral view. Anterior area of the second valvifer more than 2.0 times as high as bulb in lateral view. Apodemes of S7 without apparent modifications.

Variation

The brown colouration of the mesosoma and the anterior part of the metasoma including the synsternum and syntergum of SMNS_Hym_Cer_000446 is considerably brighter than in the holotype and the anteromedian projection of the metanoto-propodeo-metapecto-mesopectal complex is almost clear in this specimen. COI barcodes confirmed that this specimen belongs to A. kretschmanni sp. nov.

Discussion

Taxonomic placement of Aphanogmus kretschmanni Moser sp. nov.

In the Palearctic, the family Ceraphronidae contains 112 species in 6 genera. Aphanogmus Thomson, 1858 is the most species-rich genus with 52 described species ( Johnson & Musetti 2004; Buhl et al. 2010; Matsuo 2016), whilst four other genera comprise no more than six species. Aphanogmus is characterised mainly by a laterally compressed mesosoma, which is taller than broad ( Figs 1 , 3A–D ) as well as trapezoidal flagellar segments on the male antennae with sensillae at least as long as the width of the flagellar segments. Currently, Aphanogmus is separated into three species groups ( Evans et al. 2005). Morphologically, A. kretschmanni sp. nov. falls into the fumipennis species group based on a complete mesoscutal median sulcus and the presence of a gastral basal carina. In Hellén’s key, the new species keys to A. fumipennis Thomson, 1858 ( Hellén 1966) . However, A. kretschmanni is easily distinguishable from A. fumipennis by the distinct spines on S7 as well as the lack of prominent tufts of dense hairs along the outer margin of the hind coxae that are diagnostic for A. fumipennis .

Further, this new species resembles several species within the Aphanogmus hakonensis complex, i.e., A. amoratus Dessart & Alekseev, 1982 ; A. captiosus Poasszek & Dessart, 1996 , A. goniozi Dessart, 1988 ; A. hakonensis Ashmead, 1904 ; A. jarvensis (Girault, 1917) ; A. manilae (Ashmead, 1904) and A. thylax Polaszek & Dessart, 1996 . Shared morphological characters are found mainly on the mesosoma, particularly the sharp circumscutellar carina, the carinate metanotal-propodeal sulcus, the prominent anteromedian projection of the metanoto-propodeo-metapecto-mesopectal complex as well as the paired posterior propodeal projections and the lateral striations on the mesopleuron. All species within the hakonensis complex have an Indo-Australian distribution with a few occurrences in the westernmost Palearctic. They are hyperparasitoids of Hymenoptera that parasitize Lepidoptera Linnaeus, 1758 and can only be determined to species level through male genitalia ( Polaszek & Dessart 1996).

Recently, the Waterston’s evaporatorium on the 6 th metasomal tergite was discovered to be a taxonomically significant character complex in Ceraphronidae ( Ulmer et al. 2021) . Major differences in the structure of the Waterston’s evaporatoria of Aphanogmus and Ceraphron Jurine, 1807 were found and are supported by a cladistic analysis, which returned a monophyletic Aphanogmus group and a paraphyletic Ceraphron group ( Ulmer et al. 2021). Apart from Aphanogmus s. str., the Aphanogmus group includes the smaller genera Synarsis Foerster, 1878 , Gnathoceraphron Dessart & Bin, 1981 and Elysoceraphron Szelényi, 1936 based on striking similarities of the Waterston’s evaporatoria of these taxa. The Waterston’s evaporatorium of the newly described A. kretschmanni sp. nov. lacks campaniform sensilla on T5 and T6 ( Fig. 2D ), a character that is considered an autapomorphy of Elysoceraphron by Ulmer et al. (2021). However, there are several differences in external morphology that contradict the placement of the newly described species into Elysoceraphron : (1) the mesoscutellum of A. kretschmanni is rounded posteriorly rather than subrectangular, which is the diagnostic character for Elysoceraphron ; (2) the head of A. kretschmanni is significantly more transverse, a character shared by most species of Aphanogmus , than that of the Palearctic E. hungaricus Szelényi, 1936 or of the Oriental E. aadi Bijoy & Rajmohana, 2021 with the interocular distance being larger than the eye width ( A. kretschmanni : 158:146 µm; E. hungaricus : 152:228 µm; E. aadi : 146:222 µm); (3) the anteromedian projection of the metanoto-propodeo-metapecto-mesopectal complex is straight in A. kretschmanni whereas it is upcurved in Elysoceraphron .

The genus Elysoceraphron was first described based on two female specimens of Elysoceraphron hungaricus Szelényi, 1936 collected in Hungary ( Szelényi 1936). The male was described two decades later from Czechoslovakia ( Masner 1957). Since then, the genus has not received much attention. It appears only briefly in a report adding findings from Sweden and Siberia ( Dessart & Alekseev 1980), a few remarks on the taxonomic status of the genus ( Masner 1957; Dessart 1975), a short mention in two catalogues ( Muesebeck & Walkley 1956; Johnson & Musetti 2004) as well as in keys ( Dessart 1962; Alekseev 1978a, 1978b, 1995; Dessart & Cancemi 1987). Recently, a second species, Elysoceraphron aadi , was described from India ( Bijoy & Rajmohana 2021).

There has been considerable disagreement as to the validity of the genus Elysoceraphron . When the genus was established, it was hypothesised that it is closely related to Aphanogmus and to some extent also to Ceraphron ( Masner 1957; Dessart & Alekseev 1980). Masner (1957) bases the validity of Elysoceraphron mainly on the unique subrectangular form of the mesoscutellum ( Szelényi 1936). In contrast, Dessart (1975) considers Elysoceraphron along with a few other genera of Ceraphronidae , most of which are monotypic, as incertae sedis and argues that it is first and foremost for practical reasons that Elysoceraphron is classified as a discrete genus. This line of argumentation is reinforced by Dessart & Alekseev (1980) who conclude that E. hungaricus is most likely an aberrant species of Aphanogmus . One of the most recent keys to the genera of Ceraphronoidea lists Elysoceraphron within the satellite group of Aphanogmus ( Dessart & Cancemi 1987) . However, Dessart (1975) explicitly refrained from synonymising Elysoceraphron with Aphanogmus for practical rather than taxonomic reasons.

The limited number of distinguishing characters in external morphology leads us to agree with previous authors ( Dessart 1975; Dessart & Alekseev 1980) who question the validity of Elysoceraphron . The fact that A. kretschmanni sp. nov. and Elysoceraphron share characters of the Waterston’s evaporatorium (lack of campaniform sensilla on T5 and T6) further supports this. Based on a subrectangular mesoscutellum, the shape of the head and the straight shape of the anteromedian projection of the metanoto-propodeo-metapecto-mesopectal complex we place the newly described species into Aphanogmus .

Host biology and ovipositor mechanisms

From the literature that is available on Aphanogmus , species seem to parasitize one of two host types: weakly concealed hosts, which are often quite active, or well-concealed relatively inactive pupae of parasitoid Hymenoptera ( Dessart 1995) . Free-living predatory larvae of gall midges ( Cecidomyiidae Newman, 1835 ) fall into the category of weakly-concealed hosts and have been reported to be parasitised by various species of Aphanogmus (e.g., Bakke 1955; Laborius 1972; Matsuo et al. 2016). Cecidomyiids often predate mites (Acari Leach, 1817) or scale insects ( Coccidae Fallén, 1814 ) and are therefore relevant pest control agents in agriculture ( Dessart 1963). Hosts of Aphanogmus that fall into the second category (well-concealed and inactive) include various hymenopteran parasitoids such as Bethylidae Forster, 1856 (e.g., Buffington & Polaszek 2009), Ichneumonidae Latreille, 1802 (e.g., Yefremova et al. 2021), Braconidae Latreille, 1829 (e.g., Austin 1987; Peter & David 1990; Polaszek & LaSalle 1995), Cynipidae Latreille, 1802 (Buhl & O’Connor 2010), and Encyrtidae Walker, 1837 ( Ratzeburg 1852) . In these hosts, the species of Aphanogmus develop as hyperparasitoids. These opposing modes of host concealment are reflected in morphological adaptations in the ovipositor mechanism of their parasitoids ( Ernst et al. 2013). Host records for Aphanogmus from other insect orders include Coleoptera Linnaeus, 1758 ( Evans et al. 2005), Hemiptera Linnaeus, 1758 ( Dessart 1978) , Neuroptera Linnaeus, 1758 ( Sinacori et al. 1992), Thysanoptera Haliday, 1836 ( Dessart & Bournier 1971), and Trichoptera Kirby, 1813 ( Luhman et al. 1999).

For approximately 80% of species of Aphanogmus , no host data is available ( Matsuo et al. 2016). As a lack of solid host information is common in many ʻdark taxa’ of parasitoid Hymenoptera , a few studies have aimed to infer host data from ovipositor morphology of parasitoids (e.g., Le Ralec et al. 1996; Belshaw et al. 2003). In a comprehensive study on the ovipositor mechanism of Ceraphronoidea , Ernst et al. (2013) found that a larger relative distance between the anterior angle of the first valvifer (ang) and the inter-valvifer articulation (iva) allows for a larger amplitude of sliding motion of the first valvulae. It is hypothesised that a larger sliding motion of the paired first valvulae represents a rapid but less robust oviposition mechanism that would be suitable for exposed, mobile hosts ( Ernst et al. 2013). The newly described Aphanogmus kretschmanni sp. nov. corresponds to the Ceraphron type ovipositor mechanism that is characterised by a relatively large distance between the anterior angle of the first valvifer and the intervalvifer articulation. This would support the potential for a rapid oviposition in A. kretschmanni .

However, in A. kretschmanni sp. nov., the first valvifer (1vf) is angled at the tergo-valvifer articulation (tva), which is located in the middle of 1vf ( Figs 2C , 3I–K ). Overall, 1vf has an evenly convex shape in A. kretschmanni , a condition unlike any of the Ceraphronidae analysed by Ernst et al. (2013). Creator spissicornis ( Hellén, 1966) is the only other species observed by Ernst et al. (2013; therein cited as Dendrocerus spissicornis (Hellén) despite having been transferred by Alekseev in 1980) where the first valvifer is convex but its tergo-valvifer articulation is significantly closer to the anterior angle of the first valvifer than that of A. kretschmanni . Creator spissicornis parasitizes the pupae of two fly species: Macronychia striginervis (Zetterstedt, 1844) ( Sarcophagidae Macquart, 1834 ) and Zabrachia minutissim a (Zetterstedt, 1838) ( Stratiomyiidae Latreille, 1802 ) ( Alekseev 1980). The ovipositor morphology of A. kretschmanni does not unequivocally support a host association but it most likely correlated with the unique modification of the 7 th metasomal sternite discussed below.

Functional morphology of the distinctive structure on 7 th metasomal sternite

The distinctive spines on the 7 th metasomal sternite are the distinguishing character that separates this newly described species from all other species of Ceraphronidae . Modifications to the ovipositor are common across Hymenoptera , e.g., the dart-tailed epipygium in Cameronella Dalla Torre, 1897 ( Wang & Cook 2012), the heavily pubescent ovipositor of Torymus lasallei Bubeníková, Pujade-Villar & Janšta, 2020 and serrated ovipositor valvulae occur in several Symphyta Gerstaecker, 1867, Ichneumonoidea Latreille, 1802, Megalyroidea Schletterer, 1890 and Chalcidoidea Latreille, 1817 ( Quicke et al. 1994). Modifications to metasomal sternites, on the other hand, are less common but have been reported from the following braconids: the females of Kollasmosoma sentum (van Achterberg & Góme, 2011) , which parasitize adult workers of Cataglyphis ibericus (Emery, 1906) ( Formicidae Latreille, 1809 ), have a single apical spine on the penultimate 5 th metasomal sternite ( Durán & van Achterberg 2011). It is hypothesised that the spine of K. sentum fixes the wasp during oviposition and acts as a supporting point for the oviposition movements of the metasoma ( Durán & van Achterberg 2011). Further, a few Braconidae have paired or unpaired accessory prongs on the last metasomal sternite: Metaphidius Starý & Sedlag, 1959 has a short, unpaired prong at the base of the 7 th sternite whereas the paired prongs in Trioxys Haliday, 1833 and Acanthocaudus Smith, 1944 and the unpaired prong in Bioxys Starý & Schlinger, 1967 are variable in shape and size ( Starý 1976). These prongs, along with down-curved ovipositor sheaths, were observed to help retain an aphid host in place during oviposition ( Starý 1976).

Similarly, the position of the spines along the 7 th sternite in A. kretschmanni sp. nov. suggests that this modification could play a stabilising role in oviposition. In all Ceraphronoidea , oviposition is initiated by a contraction of the muscles connecting the apical tergites and sternites, which leads to a rotation of the ovipositor and thereby moves it into its active, exposed position ( Ernst et al. 2013). Along with the ovipositor, which is usually concealed by the 7 th metasomal sternite, the 9 th sternite is rotated posteriorly and thus the ovipositor is exposed. If the 7 th sternite abuts the substrate or surface of the host in the initiating moves of oviposition, the spines could be useful for anchoring the wasp’s metasoma. This could allow for the ovipositor to be inserted into the host with significantly greater force or precision. The slight anterior tilt of the spines could be seen as further support for this hypothesis.

Alternatively, the saw-like spines could be used for cutting into harder substrates. This is known from Drosophila suzukii (Matsumura, 1931) and Scaptomyza flava (Fallén, 1823) , both of which have serrated ovipositors ( Whiteman et al. 2011; Atallah et al. 2014). The serrated ovipositor gives these species the means to cut through the skin of various fruits or the surface of leaves respectively, enabling them to exploit new ecological niches in comparison to species with unserrated ovipositors ( Whiteman et al. 2011). Similarly, the distinctive spines of S7 of A. kretschmanni sp. nov. along with its less robust ovipositor mechanism might enable the wasp to access well-concealed hosts by using the spines to saw through harder substrates.

The somewhat enlarged hind tarsomeres and tarsal claws ( Fig. 3F–H ), which are slightly broader and longer compared to corresponding structures in the fore and middle legs, might be interpreted as support for either hypothesis. The adaptations in the metatarsus might help anchor the wasp to the substrate.A more extreme form of enlarged tarsal structures of the hind legs has been observed in Trassedia Cancemi, 1996 (Ceraphronoidea) , where the hind tarsomeres and hind tarsal claws are almost twice as long and wide as these structures in the preceding legs ( Mikó et al. 2018). It is hypothesised that the enlarged hind tarsomeres and tarsal claws in Trassedia are adaptations to anchoring the body while the wasp uses its chisel-shaped tip of the 7 th metasomal sternite to cut into hard substrates ( Mikó et al. 2018). This reasoning is in line with morphological characteristics in the ovipositor of Trassedia that set its mechanism apart from the ovipositor systems of all other Ceraphronoidea . In this genus, the first valvifer consists of two articulating sclerites and the tva is located very close to the iva, thus enabling the first valvulae to slide a long distance along the second valvulae ( Ernst et al. 2013). This particular combination in ovipositor morphology along with the modifications of the metasomal apex allow for accelerated oviposition by enabling the egg to move down the ovipositor extremely quickly whilst still being able to parasitize well-concealed hosts in hard substrates. These exact same conclusions cannot be drawn for A. kretschmanni sp. nov. The plesiomorphic division of the first valvifer is a feature unique to Trassedia and a few other insect taxa ( Ernst et al. 2013). Except for Trassedia , all ceraphronoids examined by Ernst et al. (2013) as well as A. kretschmanni described here, have the first valvifer not bi-partitioned into two articulating sclerites. Further, the posterior margin of the first valvifer is slightly concave in Trassedia , whereas it is convex in A. kretschmanni and the tva is located roughly between the intervalvifer articulation and the anterior angle. These characteristics limit the distance that the first valvulae can slide along the second valvulae in A. kretschmanni . Therefore, oviposition in Trassedia is expected to be significantly quicker than what is physically possible in the newly described A. kretschmanni .

Overall, the functional morphology of the ovipositor of A. kretschmanni sp. nov. points to a quick mode of oviposition that is less robust and therefore typically limited to softer substrates. This Ceraphron type ovipositor (sensu Ernst et al. 2013) is shared by many species of Aphanogmus that parasitise weakly-concealed, free-living cecidomyiid larvae. However, the distinctive spines on the 7 th sternite of A. kretschmanni might enable the wasp to access hosts that are well-concealed by sawing through a hard concealing surface. A potential hypothesis would be that A. kretschmanni retained an ovipositor mechanism best suited for quick parasitisation while at the same time overcoming the limitation of this mechanism to softer substrates through the saw-like spines on S7 that could enable the female to access well-concealed hosts. This hypothesis as well as the definitive host organism of A. kretschmanni remain yet to be proven by observation or through rearing experiments.

Figures

Fig. 1. Aphanogmus kretschmanni Moser sp. nov.; holotype, ♀ (SMNS_Hym_Cer_000227). a. Habitus, lateral view. b. Habitus, dorsal view. Scale bars = 200 µm.

Fig. 2. Detailed images of A. kretschmanni Moser sp. nov. (a, d = SMNS_Hym_Cer_000466; b = SMNS_Hym_Cer_000465; c = SMNS_Hym_Cer_000469). a. Wing interference patterns of left fore- and hindwing. b. Fore- and hindwing. c. CLSM image of ovipositor with sclerites in red. Abbreviations: 1vf = 1st valvifer; 1vv = 1st valvulae; ang = anterior angle of the 1st valvifer; asf = anterior section of the dorsal flange of the second valvifer; bl = basal line of the second valvifer; bulb = bulbous anterior area of the dorsal valve; iva = intervalvifer articulation; tva = tergo-valvifer articulation. d. Waterston’s evaporatorium on T6. Abbreviations: at cx = acrotergal calyx; ta = tergal apodeme. Scale bars: a–b = 200 µm; c–d = 50 µm.

Fig. 3. Digital reconstruction of A. kretschmanni Moser sp. nov. based on synchrotron micro-CT; holotype, ♀ (SMNS_Hym_Cer_000227). a–d. Habitus in left (a), right (b), ventral (c) and dorsal (d) aspect. e. Left antenna. f. Left foreleg. g. Left midleg. h. Left hindleg. i–k. Ovipositor in left (i), ventral (j) and dorsal (k) aspect. Abbreviations: 1vf = first valvifer; 1vv = first valvulae; asf = anterior section of dorsal flange of the second valvifer; bl = basal line of the second valvifer; bulb = bulbous anterior area of the dorsal valve; MPMM = metanoto-propodeo-metapecto-mesopectal complex; res = venom gland reservoir of the second valvifer; S7 = 7th metasomal sternite. Scale bars: a–h = 0.5 mm; i–k = 250 µm.