Pushing the limits – two new species of Pteromalus (Hymenoptera, Chalcidoidea, Pteromalidae) from Central Europe with remarkable morphology

Abstract Two new species, Pteromalus briani sp. n. and Pteromalus janstai sp. n., with unusual characters are described from the Central Plateau and the Alps in Switzerland, respectively. Pteromalus briani sp. n. is remarkable in that it has the metatibia quite abruptly expanded before the middle. This type of modification of the hind tibia is unique within the Pteromalidae and probably also the entire Chalcidoidea. It is also very rare in other parasitic wasps, where it is suspected to be associated with pheromone glands. The species is a gregarious endoparasitoid of pupae of Vanessa atalanta (Linnaeus) and Aglais urticae (Linnaeus), two common butterflies (Lepidoptera: Nymphalidae) in Europe. It is furthermore a koinobiont parasitoid ovipositing in an early larval stage of the host. The other species, Pteromalus janstai sp. n., shows a flattened mesosoma. A dorsoventrally depressed body is a unique feature within the genus Pteromalus, but known from a number species in unrelated genera and subfamilies. The two records demonstrate that it is possible to discover entirely new species with extraordinary characters even in one of the taxonomically most thoroughly explored parts of the world.


Introduction
In Western Europe the vast majority of newly discovered insect species usually belong to complexes of cryptic species. Morphologically, such new species are therefore quite similar to known species and in many cases even rather difficult to separate from those (e.g., Huber et al. 2013, Alkhatib et al. 2014, Baur et al. 2014, Schmidt et al. 2015. Today the discovery of species with an entirely distinct morphology happens quite rarely and they are then usually found in remote places such as the recently described, spectacular Cyranobracon depardieui Quicke and Butcher (Hymenoptera: Braconidae) from tropical Papua New Guinea (Butcher and Quicke 2015) or Norbanus draco Mitroiu (Hymenoptera: Pteromalidae) from Central and Southern Africa (Mitroiu 2015). Here I describe two new species of Pteromalidae (Chalcidoidea) with outstanding morphological characters from Central Europe. Although both species are clearly referable to the genus Pteromalus, some of their characters stretch the limits of the genus, and in one case the character state may not even be known in Chalcidoidea.
The genus Pteromalus contains 485 species world wide, with the majority (371 species) having been described from Europe (Noyes 2015). It is thus the most species-rich genus of Pteromalidae. All species are parasitoids of larvae and pupae of various holometabolous insects, for instance Lepidoptera, Coleoptera, gall forming Hymenoptera (Cynipidae, Tenthredinidae) and Diptera (Tephritidae). No recent study is available that delineates Pteromalus based on phylogenetic principals. However, the genus can easily be recognized by a combination of characters (Graham 1969, Bouček and Rasplus 1991, Bouček and Heydon 1997: clypeus striate, its anterior margin truncate or weakly to strongly emarginate, always without a median tooth; flagellum with 2 anelli and 6 funicular segments; clava in females symmetrical; prepectus with relatively small upper triangular area; paraspiracular sulci rather deep and usually with some transverse costulae. Pteromalus puparum (Linnaeus, 1758) and P. cerealellae (Ashmead, 1902) are among the best-known species of the genus, while for the majority of species little is known except for an occasional distributional or host record (Noyes 2015). However, some Pteromalus species attacking fruit flies (Diptera: Tephritidae) have received attention as potential biological control agents (Kapaun et al. 2010) and in community ecology (e.g., Hoffmeister 1992).
Geographical coordinates on data labels of type specimens are indicated as WGS 84 latitude and longitude.
Nomenclature and classification of Chalcidoidea follow Noyes (2015). Terminology of body parts follows Gibson (1997), for terms concerning sculpture of the integument and for some particular expressions used in the description I refer to Graham (1969). The separation of the plica of the propodeum into an anterior and a posterior plica is according to Baur (2000). The Appendix gives an overview of the basic descriptive statistics for each body measurement (in µm) and species as well as the sample sizes. The selected measurements correspond to those used in the taxonomy of Pteromalidae for calculating standard ratios (e.g., Graham 1969; see Table 1), except for body length. Body length of Pteromalidae is usually measured in dorsal view from anterior margin of head to tip of ovipositor sheaths (Graham 1969, Bouček andRasplus 1991). It is thus often quite variable due to the varying position and angle of head and gaster relative to mesosoma. I therefore have preferred to indicate body length as the sum of lengths (in mm) of head, mesosoma and gaster, each of which could be measured rather more precisely. I also give mesoscutum breadth (in µm), which is considered by Ohl and Thiele (2007) as the most universal measure of size in some Apoidea (Hymenoptera). Note that such a measure is the best way to compare the size of females and males in Chalcidoidea, since body length is usually strongly affected by sex related differences of the gaster (see Bouček 1988. Most characters were measured on photographs taken by Lisa Wilmsmeier with a Leica DFC425 camera mounted on a Leica M16 stereomicroscope. Photographs were taken at different magnifications depending on the size of the character, in order to reduce measurement error for the smaller ones. For all measurements, it was ensured that the points of reference were in perfect focus and that the diaphragm of the lens was fully open. The distances were finally measured using ImageJ, version 1.46v (Schneider et al. 2012). Body parts on the images were zoomed-in on screen up to four times before measuring. To avoid variation due to fluctuating asymmetry (e.g., Palmer andStrobeck 1986, Bechshøft et al. 2008), measurements of paired characters were taken on the left hand side.
I measured three characters, eye length, head length, and temple length, on a single stack photograph taken with a Keyence VHX 2000 digital photomicroscope and a VH-Z20R/W zoom lens at a magnification of 200× (i.e., 1000 µm corresponded to 888 pixels, see Table 1), also using ImageJ, version 1.48v. Stack photos were used because the reference points do not lie in the same focal plane. Accuracy of measurement is thus critically dependent on an exact positioning of the head in dorsal view. Naturally, measurement error should be higher for such characters. * Where more than one number is present, the first refers to the magnification used for P. briani sp. n., the second to the one used for P. janstai sp. n.
I also used the Keyence microscope for making stack-images of qualitative character states. A 4-digit individual code including the notion "Baur" (e.g., "Baur 2410") was provided for specimens that have been measured or photographed, or used as reference specimens for comparison with newly described species.
Mesoscutum: finely reticulate, meshes rather high, areoles small and only moderately enlarged in posterior part of sclerite (Fig. 1D); scutellum: reticulate, meshes about as strong and coarse as on posterior part of mesoscutum, but with a narrow band of smaller areoles in anterior half of median longitudinal line; frenum: reticulate, meshes of similar size to those on scutellum; axilla: reticulate, about as strong as on central part of scutellum; prepectus upper triangular area: reticulate; upper mesepimeron: anteriorly smooth, posterior corner distinctly alutaceous; upper mesepisternum: reticulate, about as strong as on mesoscutum; metapleuron: reticulate, about as strong as on mesepisternum.
Antenna (Fig. 1C). Antennal formula: 11263; scape reaching: distinctly above level of vertex; flagellum: filiform; first anellus: strongly transverse; second anellus: strongly transverse; first funicular segment: cylindrical; setae on flagellum: moderately thickly clothed with setae standing out at an angle of 30 degrees, length of setae less than half the breadth of flagellar segments; number of rows of longitudinal sensilla on first funicular segment: 2, on sixth: 1-2.
Mesosoma in lateral view: moderately strongly bent; propodeum in lateral view sloping with respect to dorsal plane of mesoscutum and scutellum at an angle of: 45 degrees; pronotum breadth with respect to mesoscutum breadth: distinctly narrower; pronotum collar: horizontal, well defined, its length with respect to mesoscutum length: one sixth, its anterior margin: rounded edge; pronotum posterior margin: thin, shiny strip; notaulus: extremely superficial, hardly traceable, reaching: about half along mesoscutum (Fig.  1D); scutellum in lateral view: moderately convex; scutellum in posterior view: moderately convex; scutellum posterior margin projection: level of anterior margin of dorsellum; scutellum posterior margin in posterior view: narrowly emarginate in the middle; frenal line: finely indicated, especially on sides; prepectus upper triangular area: not separated by oblique carina; upper mesepimeron: strongly narrowing below, not reaching base of mesopleuron; propodeum ( Fig. 1G): anterior plica: bent inwards in anterior two fifths and strong; posterior plica: present, joining or almost joining anterior plica; orientation of posterior plicae: almost parallel; median carina of propodeum: weakly indicated, irregular; nucha: elevated but not clearly differentiated from median area of propodeum; spiracle: oval, size: small, separated from anterior margin of propodeum by: shortest diameter; callus pilosity: numerous long setae; paraspiracular sulcus: narrow and deep.
Petiole: green with purplish tinge; gaster: green; gastral terga: one to three with an indistinct yellowish spot.
Mesoscutum: finely reticulate, meshes rather high, areoles small and only moderately enlarged in posterior part of sclerite; scutellum: reticulate, meshes about as strong and coarse as on posterior part of mesoscutum, but with a narrow band of smaller areoles in anterior half of median longitudinal line; frenum: reticulate, meshes of similar size to those on scutellum; axilla: reticulate, about as strong as on central part of scutellum; prepectus upper triangular area: reticulate; upper mesepimeron: anteriorly smooth, posterior corner distinctly alutaceous; upper mesepisternum: reticulate, about as strong as on mesoscutum; metapleuron: reticulate, about as strong as on mesepisternum.
Shape and structure: Head in frontal view: subtrapezoid; gena in frontal view: rounded; temple in dorsal view: obtuse; forming an angle with occiput of: 120 degrees; occipital carina: absent; torulus position with respect to lower ocular line: distinctly above; lower face in lateral view: flat, receding with respect to upper face: weakly, forming an angle of: 35 degrees; scrobe: narrow, rather shallow; malar sulcus: superficial, but traceable; clypeus, anterior margin: widely and shallowly emarginate, without a median depression above emarginate edge; gena near mouth: terete; tentorial pit: distinctly visible; mouth extension: not conspicuously enlarged ( Fig. 2A); mandibular formula: 4-4. Antenna (Fig. 2B). Antennal formula: 11263; scape reaching: distinctly above level of vertex; flagellum: filiform; first anellus: strongly transverse; second anellus: strongly transverse; setae on flagellum: thickly clothed with setae standing out at an angle of 40 degrees, length of setae less than half the breadth of flagellar segments; number of rows of longitudinal sensilla on first funicular segment: 1, on sixth: 1.
Mesosoma in lateral view: moderately strongly bent; propodeum in lateral view sloping with respect to dorsal plane of mesoscutum and scutellum at an angle of: 50 degrees; pronotum breadth with respect to mesoscutum breadth: distinctly narrower; pronotum collar: horizontal, well defined, its length with respect to mesoscutum length: one sixth, its anterior margin: rounded edge; pronotum posterior margin: thin, shiny strip; notaulus: extremely superficial, hardly traceable, reaching: about half along mesoscutum; scutellum in lateral view: moderately convex; scutellum in posterior view: moderately convex; scutellum posterior margin projection: level of anterior margin of dorsellum; scutellum posterior margin in posterior view: narrowly emarginate in the middle; frenal line: finely indicated, especially on sides; pre pectus upper triangular area: separated by a fine oblique carina; upper mesepimeron: strongly narrowing below, not reaching base of mesopleuron; anterior plica: bent inwards in anterior two fifths and strong; posterior plica: present, joining anterior plica; orientation of posterior plicae: almost parallel; median carina of propodeum: weakly indicated, irregular; nucha: elevated but not clearly differentiated from median area of propodeum; spiracle: oval, size: small, separated from anterior margin of propodeum by: shortest diameter; callus pilosity: numerous long setae; paraspiracular sulcus: narrow and deep.
Petiole Gaster length to breadth: 1.68-1.71; gaster length to mesosoma length: 1-1.01. Comment. Close examination of the expanded metatibia under a stereomicroscope did not reveal any distinctive characteristics compared to the "normal", i.e. unexpanded, metatibia of the other Pteromalus species. It should be noted that for some of the specimens reared from Aglais urticae the expansion is slightly less abrupt than shown in Fig. 1F.
Below the most important differences are given for those species with which P. briani sp. n. might be most easily confounded. Because of the difficulty to identify some of them, a rather large number of taxa either related to P. puparum or with similar hosts (Lepidoptera: Papilionidae, Nymphalidae or Pieridae) has been considered.
P. apum (Retzius, 1783): female femora infuscate; reticulation between clypeus and malar sulcus without enlarged meshes; POL greater than OOL; tentorial pit indistinct; antenna inserted less high on face, lower edge of torulus below the middle between anterior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view flattened; metatibia gradually widening towards apex; female gaster acuminate, often more than 1.6 times as long as broad. Source of information: 2 ♀ 2 ♂ from Switzerland in NMBE (Baur 2517(Baur -2520, also compared with the key by Askew and Shaw (1997). P. bifoveolatus (Förster, 1861): female femora infuscate; reticulation between clypeus and malar sulcus without enlarged meshes; POL slightly greater than OOL; tentorial pit indistinct; antenna high on face, lower edge of torulus at about the middle between anterior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view moderately convex; metatibia gradually widening towards apex; female gaster acuminate, often more than 1.6 times as long as broad. In addition, the male of P. bifoveolatus is special in that the mouth is very wide, so that the malar space is much less than 0.1 times as long as eye height (0.58-0.61 in P. briani sp. n.). Source of information: syntype ♂ in NHMV, 2 ♀ 2 ♂ (Baur 2521-2524) from Switzerland in NMBE.
P. cassotis Walker, 1847 (syn. P. archippi Howard, 1889Howard, : 1891: female legs except coxae testaceous; reticulation between clypeus and malar sulcus without enlarged meshes; POL about as great as OOL; tentorial pit indistinct; antenna high on face, lower edge of torulus at about the middle between anterior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view moderately convex; metatibia gradually widening towards apex; female gaster acuminate, about 1.25 times as long as broad. Source of information: photographs of lectotype ♀ in BMNH, provided by N. Dale-Skey Papilloud; lectotype ♀ of P. archippi in USNM. P. fuscipes (Provancher, 1881): The lectotype is deposited in the Laval University, Quebec, Canada (Noyes 2015;Huber, pers. comm.), but was not available for examination. The original description (see Provancher 1881: 295) suggests a species with dark legs ("Pattes brunes" = legs brown), which naturally excludes an identity with P. briani sp. n. Burks (1963Burks ( : 1262 suggested that P. fuscipes might be the same as P. p. vanessae (see also below).
P. luzonensis Gahan, 1925: female femora infuscate; reticulation between clypeus and malar sulcus without enlarged meshes; POL about as great as OOL; tentorial pit indistinct; antenna high on face, lower edge of torulus at about the middle between anterior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view moderately convex; metatibia gradually widening towards apex; female gaster obtusely pointed, 1.4-1.6 times as long as broad. Source of information: photographs of a syntype ♀ from Luzon, Mount Makiling, provided by the USNM Chalcidoidea type catalog. 5 ♀ 5 ♂ from Assam and Nepal, in BMNH, compared with the original description by Gahan (1925: 99-100).
P. melitaeae Dzhanokmen, 1998: female femora infuscate; reticulation between cly peus and malar sulcus without enlarged meshes; POL greater than OOL; tentorial pit indistinct; antenna less high on face, lower edge of torulus slightly below the middle between anterior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view moderately convex; metatibia gradually widening towards apex; female gaster acuminate, about 2.3 times as long as broad. Source of information: 2 ♀ from Switzerland in NMBE (Baur 2525(Baur , 2526, compared with a paratype 1 ♀ in BMNH and the English version of the original description by Dzhanokmen (1998).
P. platyphilus Walker, 1874: female femora infuscate; reticulation between clypeus and malar sulcus without enlarged meshes; POL greater than OOL; tentorial pit indistinct; antenna less high on face, lower edge of torulus distinctly below the middle between anterior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view moderately convex; metatibia gradually widening towards apex; female gaster obtusely pointed, about 1.3 times as long as broad. Source of information: 1 ♀ from Morocco in NMBE (Baur 2527), det. Z. Bouček 1996.
P. puparum (Linnaeus, 1758): female femora infuscate; reticulation between clypeus and malar sulcus without enlarged meshes; POL slightly greater than OOL; tentorial pit indistinct; antenna high on face, lower edge of torulus at about the middle between anterior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view moderately convex; metatibia gradually widening towards apex; female gaster obtusely pointed, rarely more than 1.6 times as long as broad. Source of information: 3 ♀ 2 ♂ from Switzerland in NMBE (Baur 2528(Baur -2531(Baur , 2549. P. puparum vanessae Howard, 1889: Harris (1841: 220-221) originally proposed the specific name "Pteromalus vanessae" but without accompanying description. Hence it has to be considered as a nomen nudum (Noyes 2015). Howard (1889: 1891-1892) who gave a brief description based on material reared from Nymphalis antiopa (Linnaeus, 1758) (sub Euvanessa antiopa) and Polygonia interrogationis (Fabricius, 1798) (both Lepidoptera: Nymphalidae), eventually made the name available. The whereabouts of the syntypes is unknown (Noyes 2015) and they thus could not be checked. However, Howard (1889) evidently considered P. p. vanessae to be only a larger and darker variety of P. puparum, of which he gave a redescription (p. 1890). The latter is said to have dark legs, which differentiates the species from P. archippi (= P. cassotis, see above) with pale legs described by Howard in the same paper (p. 1891). Therefore, P. p. vanessae also must have dark legs, which clearly separates it from P. briani sp. n. P. semotus (Walker, 1834): female femora infuscate; reticulation between clypeus and malar sulcus without enlarged meshes; POL distinctly greater than OOL; tentorial pits indistinct; antenna less high on face, lower edge of torulus slightly below the middle between anterior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view moderately convex; metatibia gradually widening towards apex; female gaster acuminate, distinctly more than twice as long as broad. Source of information: 1 ♀ from Switzerland in NMBE (Baur 2532), compared with the lectotype ♀ in BMNH.
P. smaragdus Graham, 1969: female legs except coxae bright testaceous [this is in contrast to the original description, where it is stated on p. 494 that the legs have the same color as P. procerus (Graham, 1969) which is said to have the femora infuscate (p. 493)]; reticulation between clypeus and malar sulcus without enlarged meshes; POL slightly greater than OOL; tentorial pit indistinct; antenna high on face, lower edge of torulus at about the middle between anterior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view moderately convex; metatibia gradually widening towards apex; female gaster acuminate, about 1.3 times as long as broad. Source of information: photographs of holotype ♀ in BMNH, provided by N. Dale-Skey Papilloud.
P. squamifer (Thomson, 1878): female legs except coxae testaceous (Fig. 2F); reticulation between clypeus and malar sulcus without enlarged meshes (Fig. 2C); POL slightly less than OOL (Fig. 2D); tentorial pit indistinct (Fig. 2C); antenna high on face, lower edge of torulus at about the middle between anterior margin of cly peus and anterior edge of anterior ocellus; mesoscutum with areoles large and rather strongly enlarged in posterior part of sclerite (Fig. 2E); scutellum in lateral view moderately convex; metatibia gradually widening towards apex (Fig. 2F); female gaster acuminate (Fig. 2H), 1.55-1.6 times as long as broad. As in P. bifoveolatus, the male has the mouth very large (see Graham 1969: 399, figure 338) and malar space much less than 0.1 times as long as eye height (0.58-0.61 in male P. briani sp. n., Fig. 2A). Source of information: photographs of lectotype ♀ in LUZM, provided by C. Hansson; 1 ♀ from Italy in NMBE (Baur 2533) and 4 ♀ from Sweden in BMNH (Baur 2545(Baur -2548. It should be noted that in the key of Graham (1969: 513-514) couplet 91 to P. squamifer might be misleading, in that he stated "temples about two thirds as long as eyes". In fact, my measurements on a photograph as well as on the other specimens showed that the temple is at most 0.6 times as long as the eye (Fig. 1C). This value is also strongly depending on how the head is positioned. In another photograph after re-positioning of the same specimen, the ratio was only 0.5! P. varians (Spinola, 1808): female femora varying from infuscate to testaceous; reticulation between clypeus and malar sulcus without enlarged meshes; POL distinctly greater than OOL; tentorial pits indistinct; antenna high on face, lower edge of torulus at about the middle between anterior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view moderately convex; metatibia gradually widening towards apex; female gaster acuminate, distinctly more than twice as long as broad. Source of information: 4 ♀ 1 ♂ from France, Moldavia, and Switzerland in NMBE (Baur 2534(Baur -2539, compared with lectotypes of synonyms of P. varians, that is, ♀ P. grandis Walker, 1835 and ♀ P. latipennis Walker, 1835 in BMNH. P. vopiscus Walker, 1839: female femora infuscate; reticulation between clypeus and malar sulcus without enlarged meshes; POL slightly greater than OOL; tentorial pit indistinct; antenna high on face, lower edge of torulus at about the middle between an-terior margin of clypeus and anterior edge of anterior ocellus; mesoscutum with areoles small and only moderately enlarged in posterior part of sclerite; scutellum in lateral view moderately convex; metatibia gradually widening towards apex; female gaster acuminate, often more than 1.6 times as long as broad. Source of information: 2 ♀ from Switzerland, in NMBE (Baur 2540(Baur , 2541. Identification originally based on Graham's (1995) redescription of the species, however, the specimens were later also compared with specimens from Southern France in BMNH identified by Graham himself.
Etymology. Following the suggestion of the collector of the new species, Jacqueline Grosjean, Pteromalus briani sp. n. is named after Brian Jones, since the V. atalanta pupa was collected on his birthday. The name "briani" is a noun in the genitive case and need not agree in gender with the generic name.
Biology. Pteromalus briani sp. n. is a gregarious, primary endoparasitoid of pupae of Nymphalidae (Lepidoptera). Currently, Vanessa atalanta and Aglais urticae are known as hosts but the species is likely to attack pupae of other nymphalids or possibly of related families. About 58-60 specimens emerged from the overwintering pupa of V. atalanta (only 51 ♀, 2 ♂ preserved). According to Rahel Schnidrig (pers. com.) about 40-50 specimens emerged from the pupa of Aglais urticae but only 6 ♀ were preserved. The investigation of Schnidrig suggests a koinobiont life history strategy, because the host was collected in an early larval stage (body length 2.5 mm), which was afterwards protected from further parasitization during captive rearing.
Petiole: dark purplish; gaster: green to blue-green with metallic luster; gastral terga: one to five with strong purplish tinge.
Mesoscutum: finely reticulate, meshes moderately high, areoles small and not enlarged in posterior part of sclerite; scutellum: reticulate, meshes about as strong and coarse as on posterior part of mesoscutum; frenum: reticulate, meshes larger than those on scutellum; axilla: reticulate, about as strong as on central part of scutellum; pre pectus upper triangular area: weakly reticulate; upper mesepimeron: anteriorly smooth, posterior corner distinctly alutaceous; upper mesepisternum: reticulate, about as strong than on mesoscutum; metapleuron: weakly reticulate, less strong as on mesepisternum.
Coxae: weakly reticulate. Median area of propodeum: uniformly reticulate, as strong as on mesoscutum; inner corner of anterior plica: with a smooth depression and transverse carinae; nucha: reticulate, as strong as on median area of propodeum; callus of propodeum: weakly reticulate; paraspiracular sulcus: smooth with few transverse costulae.
Mesosoma in lateral view: rather flattened; propodeum in lateral view sloping with respect to dorsal plane of mesoscutum and scutellum at an angle of: 20 degrees (Fig.  3D); pronotum breadth with respect to mesoscutum breadth: distinctly narrower; pronotum collar: horizontal, well defined, its length with respect to mesoscutum length: one sixth, its anterior margin: finely carinate; pronotum posterior margin: thin, shiny strip; notaulus: superficial, reaching: two thirds along mesoscutum; scutellum in lateral view: almost flat; scutellum in posterior view: almost flat medially; scutellum posterior margin projection: level of anterior margin of dorsellum; scutellum posterior margin in posterior view: straight; frenal line: finely indicated, especially on sides; prepectus upper triangular area: separated by a strong carina; upper mesepimeron: strongly narrowing below, not reaching base of mesopleuron; propodeum (Fig. 3F): anterior plica: present, almost straight in anterior part; posterior plica: present, joining or almost joining anterior plica; orientation of posterior plicae: almost parallel; median carina of propodeum: mostly effaced; nucha: elevated but not clearly differentiated from median area of propodeum; spiracle: oval, size: small, separated from anterior margin of propodeum by: shortest diameter; callus pilosity: relatively sparsely setose; paraspiracular sulcus: narrow and deep.
Mesoscutum: finely reticulate, meshes moderately high, areoles small and not enlarged in posterior part of sclerite; scutellum: weakly reticulate, meshes less strong and coarse than on posterior part of mesoscutum; frenum: weakly reticulate, meshes larger than those on scutellum; axilla: reticulate, about as strong as on lateral part of scutellum; prepectus upper triangular area: weakly reticulate; upper mesepimeron: anteriorly smooth, posterior corner distinctly alutaceous; upper mesepisternum: reticulate, about as strong as on mesoscutum; metapleuron: weakly reticulate, less strong than on mesepisternum.
Pro-and mesocoxa: finely alutaceous, metacoxa: finely reticulate. Median area of propodeum: uniformly reticulate, as strong as on mesoscutum but with smaller meshes; inner corner of anterior plica: with a smooth depression and transverse carinae; nucha: reticulate, as strong as on median area of propodeum; callus of propodeum: weakly reticulate; paraspiracular sulcus: smooth with few transverse costulae.
Shape and structure: Head in frontal view: subtrapezoid; gena in frontal view: buccate; temple in dorsal view: obtuse; occipital carina: absent; torulus position with respect to lower ocular line: distinctly above; lower face in lateral view: rather flat, receding with respect to upper face: weakly, forming an angle of: 35 degrees; scrobe: narrow, moderately deep; malar sulcus: superficial, but traceable; clypeus, anterior margin: widely and shallowly emarginate, medially slightly inclined above anterior edge; gena near mouth: terete; tentorial pit: indistinct; mouth extension: not conspicuously enlarged; mandibular formula: ?3-4 (the mandibles are in the single male concealed, but the mandibular formula is most likely the same as in females).
Mesosoma in lateral view: rather flattened; propodeum in lateral view sloping with respect to dorsal plane of mesoscutum and scutellum at an angle of: about 25 degrees; pronotum breadth with respect to mesoscutum breadth: distinctly narrower; pronotum collar: horizontal, well defined, its length with respect to mesoscutum length: one sixth, its anterior margin: slightly elevated edge, medially carinate; pronotum posterior margin: thin, shiny strip; notaulus: superficial, reaching: two thirds along mesoscutum; scutellum in lateral view: almost flat; scutellum in posterior view: almost flat medially; scutellum posterior margin projection: level of anterior margin of dorsellum; scutellum posterior margin in posterior view: narrowly emarginate in the middle; frenal line: finely indicated, especially on sides; prepectus upper triangular area: ? (the lower part of the prepectus is concealed in the single male, but the character state is likely to be the same as for the females); upper mesepimeron: strongly narrowing below, not reaching base of mesopleuron; anterior plica: present, almost straight in anterior part; posterior plica: present, joining anterior plica; orientation of posterior plicae: almost parallel; median carina of propodeum: anteriorly indicated, effaced posteriorly; nucha: elevated but not clearly differentiated from median area of propodeum; spiracle: oval, size: small, separated from anterior margin of propodeum by: shortest diameter; callus pilosity: relatively sparsely setose; paraspiracular sulcus: narrow and deep.
Fore wing apex with respect to apex of gaster when folded back: not exceeding; basal cell number of setae: with up to 10 setae in distal part; basal setal line: complete, with: 11 setae; cubital setal line: incomplete, with: 4 setae; costal cell pilosity on dorsal side: bare; costal cell pilosity on lower side: with numerous setae in distal half and a complete setal line extending to base; speculum on upper side: bare, widely open below; fore wing disc: moderately thickly pilose; marginal setae: present, short; stigma: subrectangular, small; uncus: short.
Length and body ratios: Comment. The dorsoventrally compressed mesosoma and the shape of the propodeum allowed an easy association of the females with the male even though they were collected in separate localities (about 160 km as the crow flies).
Diagnosis. P. janstai sp. n. is distinguished from all known species of Pteromalus species by the following combination of characters: mesosoma strongly flattened; female gaster elongate, laterally strongly compressed, more than 5 times as long as broad.
Etymology. Pteromalus janstai sp. n. is named after Petr Jansta, who collected the female specimens. The name "janstai" is a noun in the genitive case and need not agree in gender with the generic name.
Biology. Host unknown. The females of Pteromalus janstai sp. n. were swept on some isolated Larch trees (Larix decidua) in an Alpine meadow. The male was swept in a similar habitat, but it cannot be determined whether it was swept from trees.

Discussion
Although the two new species are clearly placed within the genus Pteromalus, their morphology and some life history traits are remarkable and merit discussion. The most notable morphological feature concerns the metatibia of P. briani sp. n. Its abrupt expansion in proximal half is unique, not only within the genus but also within the family Pteromalidae and -as far as I can judge -the entire Chalcidoidea. Expansions of tibiae are known from some Pteromalidae, but here they look quite different. For instance, in Spathopus (Pireninae) the metatibia is conspicuously but very uniformly swollen only in males. Furthermore, the mesotibia of males of some Mesopolobus, Pegopus, and Spaniopus (Pteromalinae) differs in that the expansion is accompanied by a flattening or at least lateral compression of the tibia (Graham 1969, Bouček 1972). In the case of Mesopolobus the mesotibia also shows some special processes and coloration (Graham 1969, Mitroiu 2010. While such an ornamentation may play a role in courtship or during mating (Assem 1974; reviewed by Wehling 1986), a possible behavioral function of the expanded metatibia in P. briani sp. n. remains unknown.
The expansion of the metatibia is a very rare phenomenon in parasitoid wasps. Quicke and Falco (1998) have reported for Vipio moneilemae Gahan, 1930 a putative pheromone gland associated modification, which they assumed is unique within the Braconidae. Here, the swelling is present only in males and the dorsal side of the tibia has a longitudinal groove bordered by lateral ridges. In P. briani sp. n., the expansion is the same in both sexes and is not accompanied by a structural modification of the integument. However, only the use of scanning electron microscopy and histological serial sections of fresh material could possibly reveal the structure and function of this particular character. Special attention should be paid to the presence of metatibial glands, such as those found in some aculeate Hymenoptera (Hölldobler et al. 1996).
The rearing of the host larva under protected condition suggests that P. briani sp. n. develops as a gregarious, koinobiont endoparasitoid, since the host was allowed to continue its development after oviposition in an early larval stage and was only killed in the pupal stage. This is in contrast to some related gregarious endoparasitoids of Lepidoptera pupa. For instance, P. puparum, a widespread parasitoid of Papilionidae and Pieridae, immobilizes the pupal stage of its host on which the development also takes place (Takagi 1985(Takagi , 1986(Takagi , 1987). This species thus shows an idiobiont life history strategy (Fortuna et al. 2012).
Overview of 41 measurements (in µm) of Pteromalus briani sp. n. and P. janstai sp. n., showing minimum, maximum, mean, and standard deviation (except for P. janstai male with n = 1). For character name and definition, see Table 1.