Unidentified European Piogaster males

Figs 24, 25

While there have been at least 37 male specimens collected in Europe (Fig. 32), we were unable to associate any of them with the females of any of the four described European species (P. albina, P. pilosator, P. lucida, and P. punctulata). This difficulty appears to result from two factors: strong sexual dimorphism between males and females and the morphological similarity among male specimens.

Sexual dimorphism complicates these associations. Piogaster males and females of the same species vary in colour and sculpture (see P. daisetsuzana female and male specimens in Figs 7, 8, 9, 10), with males tending have darker bodies and legs lacking the stripes that are typical of females, as one example. A similar pattern appears to occur in European species. Although at least 31 female P. pilosator are known from collections, and additional photos of female specimens exist online, to our knowledge there are no male specimens that have similar morphology to these females.

In addition to sexual dimorphism, European males appear to be morphologically cryptic. Male Piogaster have been collected from a wide geographic distribution in Europe (Fig. 32), yet we found very little morphological variation between these specimens. The few characters that do vary (e. g., colour of the face and coxae, strength of metasomal grooves, and presence of a short epomia) may represent intraspecific variation rather than species-level differences. In addition, much of the variation that exists between male specimens is likely not species level variation, as highlighted in the comments detailing variation between six males collected at the same locality in Italy on 25–28 May 1990. Consequently, we were unable to identify diagnostic characters that would allow reliable differentiation of European males or their association with known females.

Molecular data have so far not resolved these associations. Two European male specimens have been DNA barcoded (Figs 1, 2, Suppl. material 2), but neither could be confidently linked to females. One specimen collected in Norway showed unstable (rogue-like) placement in both COI phylogenies (Figs 1, 2) with low bootstrap support and did not cluster within a species clade in either case. A portion of this specimens COI sequence was removed prior to phylogenetic analysis due to frame shift mutations in the alignment. Chromatograms were not available, but the unstable placement of this specimen may reflect lower-quality sequencing or base-calling errors. Another specimen collected in Germany clustered within the P. albina + P. pilosator mixed clade, but morphological examination could not link it definitively to either species.

We examined 16 European male specimens, and the description of those specimens is included below. This description is provided to detail the similarity of these male specimens, highlight the differences between males and females, and provide characters to distinguish these males from the Nearctic male specimen and the two P. daisetsuzana males.

Description. Adult. Male. Clypeus subpolished to polished, smooth with sparse setaceous punctation (Fig. 24 C, D). Face subpolished to polished, weakly rugulose and densely, weakly punctate (Fig. 24 C, D). Frons (Fig. 24 D) and vertex (Fig. 24 E) subpolished to polished, punctulate. Occipital carina complete (Fig. 24 E). Mesosoma. Pronotum with epomia usually absent, sometimes present in the dorsal pronotal groove but weak and short; polished, ventrally smooth without setae, dorsally punctate with dense setae (Fig. 25 B). Mesoscutum subpolished to polished, densely punctate, with dense setae (Fig. 25 A). Scutellum subpolished, densely shallowly punctate, with dense setae (Fig. 25 A). Mesopleuron polished, with fine sparse setiferous punctation, dorsoposterior area smooth, without setae (Fig. 25 C). Metapleuron polished, weakly punctate, with sparse setae (Fig. 25 D). Propodeum subpolished, rugose, rugose punctate, or rugulose punctate, with dense setae (lacking transverse striations as in male of P. daisetsuzana), with a longitudinal groove medially, especially anteriorly in most specimens (Fig. 25 E). Propodeum with pleural carina complete, sometimes weak and / or sinuous posterior to spiracle; lateral and medial longitudinal carinae (Fig. 25 E) variable, present in posterior, anterior, or complete. Wings. Fore wing. Vein Rs + M usually with ramellus absent, sometimes ramellus present for 0.1 × length of 2 rs-m (Fig. 25 F). Vein 2 rs-m 0.5–0.7 × as long as M between 2 rs-m and 2 m-cu (Fig. 25 F). Vein 2 m-cu not thickened or angulate between bullae (Fig. 25 F). Hind wing. Vein 1 / Cu & cu-a inclivous, angled apically where 2 / Cu intercepts, 2 / Cu intercepting in lower 0.2–0.4, 2 / Cu long and nebulous or spectral, sometimes with short tubular section basally (Fig. 25 F). Metasoma. T 1 subpolished, punctate reticulate with dense setae (Fig. 25 G). T 1 median dorsal carina 0.8–1.0 × length of T 1 (Fig. 25 G); dorsolateral carina complete (Fig. 25 G). T 2 – T 5 subpolished, T 2 – T 4 punctate reticulate, T 5 – T 6 punctate, with dense setae (Fig. 25 H). T 7 – T 8 subpolished to polished, finely punctate, with dense long yellow setae (Fig. 25 H). Tergites often with weak medial to posterior grooves (Fig. 25 H) on T 2, T 3, and / or T 4, sometimes grooves deep, sometimes without grooves, sometimes with weak anterior submedial tubercles on T 2 and T 3. Colour. Head dark brown to black, except for the following areas: face variable from fully dark brown to black (Fig. 24 C) to primarily dark brown to black with yellow to white markings (Fig. 24 D), malar space yellow to white, clypeus white to yellow to dark brown to black. Vertex dark brown to black, usually with yellow to white mark in varying shapes and sizes (Fig. 24 E). Mandible dark brown to black, apically red-brown on ventral and / or dorsal tooth, with or without basoventral yellow to brown-red spot. Maxillary and labial palps yellow to brown yellow (Fig. 24 A). Antenna medium brown, pedicel and basal 10–14 flagellomeres white to yellow ventrally (Fig. 24 A). Mesosoma dark brown to black except for the following: tegula white to pale yellow (Fig. 25 C), mesopleuron sometimes with white to yellow subtegular ridge (Fig. 25 C). Wings hyaline, veins light brown (Fig. 25 F). Fore leg coxa yellow-white (Fig. 25 C) to medium brown (Fig. 24 A), remaining leg yellow (Fig. 24 A). Middle coxa primarily yellow-white and medium brown basally to completely dark brown, remaining leg yellow (Fig. 25 A). Hind leg coxa primarily medium to dark brown, femur yellow to medium brown, tibia white to yellow with medium brown longitudinal stripe dorsally, tarsi yellow with medium brown longitudinal stripe dorsally (Fig. 25 A). Metasomal tergites uniformly medium brown to black (Fig. 25 H).

Material examined. England • 1 ♂; South East England, Theydon Bois; 30. viii. 1954; J. A & D. J. Clark; B. M. 1954-539; NHMUK 015215322; [NHMUK] • 1 ♂; Norfolk, Santon Downham; 2–11. vi. 1983; J. P. Field; Malaise trap; heath with birch and pine; RMSNH 1986.021; CNC 310414; [NMS]. France • 1 ♂; Bouches-du-Rhone / Provence, Fos-sur-Mer; 13. ix. 1962; Aubert; [MZLS] • 1 ♂; Corse Pirio, Valée du Fango; 25. v – 3. vi. 1997; Claire Villemant; Malaise trap; holm oak grove; MNHN -EY-EY 36003; [MNHN] • 2 ♂♂; Lot-et-Garonne, Bernac; 27–31. v. 1991; R. R. Askew; Malaise trap; CNC 1754569, CNC 1754570 [NMS] • 3 ♂♂; same data for preceding; 26–30. v. 1986; Quercus / Juniperus / Cornus; CNC 1754546, CNC 1754547, CNC 1754548 [NMS]. Germany • 1 ♂; Rhineland-Palatinate, Kreis Ahrweiler, Landskrone; 50.552°N, 7.17°E; 194 m; 16. v. 2014; B. Rulik; Malaise trap; BOLD: GMGMI 875-14; BIOUG 17116 - B 03; [ZFMK]. Italy • 4 ♂♂; Trento, Riva del Garda; 250 m; 25. v. 1990; C. J. Zwakhals; RMNH. INS. 1561208, RMNH. INS. 1561209, RMNH. INS. 1561212, RMNH. INS. 1561213; [RMNH] • 2 ♂♂; same data for preceding; 28. v. 1990; RMNH. INS. 1561210, RMNH. INS. 1561211; [RMNH]. Norway • 1 ♂; Telemark, Drangedal, Gjeskefjell Mountain; 59.00275°N, 8.91627°E; 26. v – 11. vi. 2020; Arnstein Staverløkk; window trap; [NINA] (photo only) • 1 ♂; Hordaland, Sveio, Moelstre; 59.5161°N, 5.27878°E; 15–30. vi. 2019; Håkon Haraldseide; Malaise trap; BOLD: COLHH 2702-19; [private collection of H. Haraldseide] (photo only).

Comments. The male Piogaster from Italy represent the first record of the genus for Italy. Fourteen male specimens were collected at the same locality between May 25 and 31, 1990, and therefore likely represent the same species. However, the six specimens of these fourteen examined as part of this study vary in the colour of the clypeus, malar space, and face (compare Fig. 24 C with uniform colour to Fig. 24 D with the maximal yellow markings found in these specimens), colour of the fore and middle coxae (primarily yellow-white versus entirely medium brown), strength of metasomal grooves (weak versus strong on T 2 and T 3), and presence or absence of a short epomia. If these specimens are conspecific, this indicates that the variable characters listed above are not reliable for diagnosing species based on males. We attempted to sequence the COI barcoding region of three of these specimens but were unsuccessful.

Two historical male-female associations have been suggested based on collection data but lack morphological support. First, Perkins (1958) described a male as possibly being P. punctulata based on superficial resemblance to the female. Male Piogaster specimens are commonly identified as P. punctulata as they are most similar morphologically to the female holotype of P. punctulata (Figs 16, 17), particularly the polished, sparsely punctate mesopleuron. We were unable to locate this male to examine it as part of this study. Second, Aubert (1963) described a male Piogaster from southern France (Fos-sur-Mer) as P. albina based on its collection alongside multiple females of that species (Aubert 1965). Our examination found no morphological evidence supporting (or refuting) this identification and P. pilosator has also been collected in close proximity (Fig. 30), including a syntype collected at Èze (Aubert 1958) and three specimens collected in St. Tropez (Suppl. material 1: Specimen data). This specimen is old and would be unlikely to result in an extraction with a high enough concentration to successfully amplify the COI barcoding gene using a standard PCR protocol, so we did not attempt this.

In addition to these historical published associations, we examined two male specimens collected in Lot-et-Garrone, France (May 27–31, 1991) that were likely associated with a female P. pilosator collected at the same site a month later. While these males are likely P. pilosator, we could not find anything morphological in our examination of these males that connects them to the P. pilosator female.