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Revision of the World species of Xeris Costa (Hymenoptera: Siricidae)
CJAI 28 -- September 25, 2015
doi: 10.3752/cjai.2015.28
Henri Goulet1, Caroline Boudreault1 and Nathen M. Schiff2

1. Genus Xeris A. Costa

Fig. C1.1 (live female)

Xeris A. Costa, 1894: 259. Type species: Ichneumon spectrum Linnaeus, 1758; monotypic. Konow, 1896: 41; Ashmead, 1898: 179; Konow, 1898a: 73–74; Konow, 1905a: 9; Konow, 1905b: 125–128; Schmiedeknecht, 1907: 769–772; Bradley, 1913: 5, 6, 8, 22, 23; Enslin, 1918: 705, 71; Schmiedeknecht, 1930 72; Hedicke, 1930: 74; Bradley, 1934: 145; Gussakovskij, 1935 2, 1: 47, 64–66, 343; Ross, 1937: 112; Hedicke, 1938: 23 (catalog); Takeuchi, 1938: 194–195; Benson, 1943: 34, 38; Berland, 1947: 72–74; Maa, 1949: 78–89; Benson, 1951: 22; Ries, 1951: 84 (catalog); Takeuchi, 1955: 3, 6, 8; Glowacki, 1956: 14; Burks, 1958: 17 (catalog); Takeuchi, 1962: 6, 11; Okutani, 1963: 24, 25; Burks, 1967: 27 (catalog); Middlekauff, 1960: 68; Smith, 1978: 83–84 (catalog); Smith, 1979: 129 (catalog); Viitasaari,  1984: 37; Vasu and Saini, 1999: 274 (in part); Saini, 2009: 65, 68, 79–80 (in part) (catalog); Taeger et al., 2010: 105 (catalog).

Sirex: Jurine, 1807: 76–79 (in part); Taschenberg, 1866: 29–30 (in part); Dalla Torre, 1894: 392–393 (in part); Konow, 1896: 41 (in part).

Urocerus: Lepeletier & Serville, 1828: 769; Leach, 1830: (9): 141.

Neoxeris Saini & Singh, 1987: 177. Type species: Neoxeris melanocephala Saini and Singh; monotypic. Saini, 2009: 67; Taeger et al., 2010: 100 (catalog). Synonym by Schiff et al., 2012: 244.

Diagnostic combination

Both sexes of Xeris are easily distinguished from all known extant genera of Siricidae by the gena with a small vertical ridge posterior to the eye. In addition, there is one metatibial spur and no anal cell on the hind wing.


Color. Black portions of body without metallic reflections. Head and thorax mainly to completely black; with white spot almost always present in dorsal 0.5; abdomen mainly reddish brown or black. Legs and antennae variously patterned with black and light reddish brown. Wings completely or partly darkly tinted or mainly clear.
Head. Antennal sockets with distance between their inner edges 1.4–2.0 times distance between outer edge of socket and nearest edge of eye (Fig. C1.2). Distance between nearest eye and lateral ocellus edges 0.9–1.7 times as long as distance between inner edges of lateral ocelli (Figs. C1.4 and C1.5). Minimum distance between inner edges of eyes about 1.3–1.7 times as long as maximum eye height (Fig. C1.3). Gena with ridge behind eye (Fig. C1.6), and in lower 0.5 with posterior edge of pits not elevated. Head with setae sharp at apex. Antenna with 14 or more flagellomeres (smallest specimens have the lowest number), and middle flagellomeres in dorsal view 3.0–4.0 times as long as high (Fig. C1.7); in female apical 5–10 flagellomeres with sensory oval impressions on dorsal and ventral surfaces, in male with sensory oval impressions only on ventral surface; in female middle and basal flagellomeres with sensory pits over most surfaces except outer surface, in male with sensory pits over inner surface and a small section of outer surface.
Thorax. Pronotum smooth on anterior vertical surface. Mesoscutum densely pitted only over median 0.7, fine microsculpture on lateral 0.3 with isolated pits with anterolateral edge raised, and with notauli clearly outlined in anterior 0.3 (Fig. C1.8). Mesotarsomere 1 in lateral view not enlarged, its dorsal and ventral edges almost parallel, and base of tarsomere 0.7 or less its maximum height. In female metatarsomere 2 in lateral view with dorsal edge 4.0–6.0 times as long as maximum height (Fig. C1.9a). Metatarsomere 5 0.5–0.7 as long as metatarsomere 2 (Fig. C1.9b). Metatibia with one apical spur (Fig. C1.11), in male in lateral view 5.5–9.0 times as long as maximum width (Fig. C1.10). Fore wing with apex acutely and angularly rounded, with vein 2r–m present and joined to cell 2M, with cell 1Rs2 clearly wider than long, with cell 3R1 3.5–4.5 times as wide as long, with vein 2r-rs joining stigma near middle, with stigma gradually attenuated even distal to junction with vein 2r-rs, with vein Rs (originating from vein 1r-rs) meeting Rs+M clearly before vein M, without vein Cu1, with vein 1cu–a joining vein Cu close to M (Fig. C1.12), and with vein 3A long, stump-like or absent. Hind wing with hamuli clearly present basal and apical to junction of veins R1 and C, and without anal cell (Fig. C1.13).
Abdomen. Female. Tergum 9 with lateral edges of median basin markedly divergent, straight anteriorly then rounded in posterior 0.5, sharply outlined for about 0.5 as long as median length of basin, and with base (outlined by black furrows laterally) 0.5–0.9 times as wide as median length of basin (Fig. C1.14). Tergum 10 with cornus in dorsal view long, narrow, and lateral edges either constricted near middle or not (Figs. C1.14 and C1.15), with cercus present but very small (Fig. C1.16). Sheath. Length of basal section 0.2–0.6 as long as apical section (Figs. B2.12, B2.12 and B2.14); apical section with lateral surface sharply folded except at very base and apex (Fig. B2.13, insert) or not folded (Fig. B2.12, insert), and without teeth in apical third of dorsal margin (Fig. C1.19). Ovipositor. Lancet with any of annuli 3–10 aligned with junction of basal and apical sections of sheath; first tooth annulus with ridge on ventral edge and with shallow, and with long and open ended pit (Fig. C1.18); in X. tarsalis with large pit in each annulus from annulus 2 up to teeth annuli (Fig. C1.17, base, middle and apex) or, in most species, 4–7 annuli anterior to teeth annuli each with a small pit (the pit of each of this group annuli decreasing in size anteriorly) (Fig. C1.18, apex), the following anterior annuli with or without a very small pit (Fig. C1.18, base and middle); edge of last 5–7 annuli before teeth annuli ventral to pit sharply and acutely produced (Fig. C1.18, apex), and edge of last 7–14 annuli before teeth annuli extending as a sharp ridge to ventral edge of lancet (Fig. C1.17, apex).

Taxonomic notes

Following the study of one paratype of Neoxeris melanocephala M. S. Saini and D. Singh, we confirmed that it is a typical member of the genus Xeris. This supports its synonymy by Schiff et al. (2012) under Xeris based then only on the description of Neoxeris.

Notes on affinities

Xeris is a natural lineage at the base of the Tremicinae (Schiff 2012). Though we did not succeed in doing a complete phylogenetic reconstruction of Xeris species, we are able to define the earliest lineage based on good evidence and to characterize some of the remaining lineages. The main problems in the phylogenetic reconstruction of Xeris are that the states of many characters differ only in degree (e.g., long and short, dense and scattered, few and many, etc.) and color pattern. The general color patterns of many Siricidae match that of many stinging insects. Such character states are highly subject to convergent evolution, and obscure relationships (e.g., females of Tremex  columba (Linnaeus), may have up to three discrete patterns in some areas of the United States (Schiff et al. 2012)).
            The pivotal characters are the ovipositor and its sheath, and to some extent the density of pits on the vertex, relative size of the eye, and the cornus.
            Principles and methods of cladistic analysis and phylogenetic reconstruction are based mainly on Hennig (1966). For each lineage, an indented list of characters is given. For each character, the derived state is given first, followed, in brackets, by the ancestral state and its distribution within Xeris or in Siricidae.
1a        Xeris tarsalis is defined by the followingderived character states:
            -     Maximum width of gena in dorsal view equal or less than that maximum distance between outer edges of eyes (in frontal view, outer edges of eyes touching or slightly intersecting genae) (Fig. B2.4). [In almost all extant species of Siricidae, the maximum width of the genae in dorsal view is clearly greater than the maximum distance between the outer edges of eyes (Fig. B2.5).]
            -     Pronotum laterally with raised reticulate ridges enclosing one or usually more pits (Fig. B2.15). [In Siricidae, the lateral surface of the pronotum is pitted, and where densely so, the pits are polygonal with their edges forming a coarse net-like pattern (Fig. B2.97).]
1aa       All remaining species of Xeris (15 species) form a monophyletic group, united by the following shared derived character states:
            -     Ovipositor sheath with median ridge (Fig. B2.13, insert). [In Symphyta, the ridge is not present (Fig. B2.12, insert).]
            -     Ovipositor sheath with basal section at most 0.45 as long as apical section (Fig. B2.12). [In Siricidae and Symphyta, the basal section is greater than 0.5 as long as the apical section (Fig. B2.13 and B2.14).]
            -     Ovipositor with basal annuli hardly outlined, at most with a very small pit (Fig. A3.3, see basal and middle annuli and associated pit of ovipositor); larger pits present on the 4–7 apical annuli before tooth annuli; apical annuli with largest pit, then pits decreasing in size on anterior 4–6 annuli (Fig. A3.3, see apex of ovipositor). [In most Siricidae, pits are large and present from annulus 2 to first tooth annulus (Fig. B2.16, base, middle and apex), in some species pits are not present at the base but are not organized as above.]
            -     Ovipositor sheath with junction between the basal and apical sections aligned between 2nd and 5th annulus. [In Siricidae with annuli extending to the base of the ovipositor, the alignment is between the 8th and 15th annulus.]
            -     Vertex with pits covering over 0.6–0.9 of surface with a small to large smooth surface centered on postocellar furrow (Figs. B2.2 and B2.3). [In Siricidae, the pits, when present, are evenly spread out without a distinct smooth area around postocellar area bordered more laterally by dense pits (Fig. B2.1).]
            -     Cornus clearly constricted near middle (Fig. C1.15). [In most extant Siricidae, the cornus is not constricted or, if constricted, then it is toward the base not the middle (Fig. C1.14).]

1b        Xeris tropicalis is defined by the following derived character state:
-     Gena with transverse ridge above mandible rounded and with large pits (Fig. B2.17). [In Siricidae and all other species of Xeris, the ridge is sharply outlined and without pits (Fig. B2.18)].
1bb      Remaining species of Xeris (14 species) form a monophyletic group, united by the following shared derived character states:
-     The distance between the outer edge of a lateral ocellus and the nearest edge of the eye is clearly longer (1.1–1.5 times) than the distance between the inner edges of the lateral ocelli (Fig. B2.20). [In most Symphyta and all extant Siricidae, the distance between the outer edge of a lateral ocellus and the nearest inner eye edge is about equal to the distance between the inner edges of the lateral ocelli (Figs. B2.1 and B2.2).]
-     The eye relative to head height is relatively small (0.34–0.53) (Fis. B2.8). [In Siricidae, the eye relative to the head height is large (Figs. B2.6 and B2.7).]
-     Vertex with a larger smooth surface around the postocellar region (Fig. B2.3). [In Siricidae, the pits, when present, are evenly spread apart with a distinct smooth area around postocellar area bordered more laterally by dense pits (Figs. B2.1 and B2.2)].

We are unable to reconstruct the next lineage because we have only two characters, giving different outcomes. The males of the following species have a white spot at the base of the metatibia (X. chiricahua, X. himalayensis, X. malaisei, X. pallicoxae, X.  spectrum, X. umbra, X. xanthoceros and X. xylocola) (Fig. B2.70). If these form a natural lineage this choice would suggests that species with reduce number and size of pits on the vertex had evolved twice (once for X. caudatus and X. melancholicus, and again for the species mentioned above). The following species have a complete white band on the pronotum laterally in males at least (X. caudatus, X. chiricahua, X. himalayensis, X. malaisei, X. melancholicus, X. pallicoxae, X. spectrum,) (Fig. B2.95). If these form a natural lineage this choice would support that species with reduced number and size of pits on the vertex share a common ancestor. However, we have no data for X. cobosi and X. xanthoceros as the males are unknown. Therefore, the best thing is to define three natural groups among the 14 species. We cannot determine the relationships for three species (X. chiricahua, X. himalayensis and X, cobosi) as we found no shared and derived character state. Among the remaining eleven species, we recognize three natural lineages. The indecisus, the caudatus and the spectrum lineages, defined as follows.

The indecisus lineage (X. indecisus, X. degrooti and X. morrisoni) forms a monophyletic group, united by the following shared derived character state:

-     In female, flagellum light reddish brown on at least apical 0.3 (Figs. B2.73, B2.74 and B2.75). [In all other species of Xeris except females of X. malaisei, X. xanthoceros and X. xylocola, the flagellum is completely black (Fig. B2.64).]
The caudatus lineage   (X. caudatus and X. melancholicus) forms a monophyletic group, united by the following shared derived character state:
-     Gena with pits very few and usually very small (Fig. B2.47). [In all other species of Xeris, pits are more numerous and larger in diameter (Figs. B2.46 and Fig. B2.138).]

The spectrum lineage (X. malaisei, X. spectrum, X. pallicoxae, X. umbra, X. xanthoceros and X. xylocola) forms a monophyletic group, united by the following shared derived character states:

-     Fore wing with cell C light yellow (Fig. B2.40). [In all other species of Xeris, the cell C is more darkly tinted (Fig. B2.39).]
-     Fore wing with vein R near base of stigma on both sides of junction with vein 1r-rs contrastingly white (Fig. B2.40). [In all other species of Xeris, the vein R near base of stigma is dark brown even at the junction with vein 1r-rs (Fig. B2.39).]

Diversity and distribution

Xeris is a moderate sized genus with 16 species. We recognize eight species from Eurasia and eight from the New World. There are no shared species. This is quite a different diversity of species than is recorded in the latest catalogs (Taeger and Blank 2011, Taeger et al. 2010) were two species were recorded from Eurasia, three from North America, and one Holarctic for a total of five species. All species occur in the northern hemisphere. In Eurasia they are recorded across temperate and boreal regions from coast to coast, and in southern regions they are restricted to high mountains in Morocco, India, China and Taiwan. In the New World they are recorded from southern Mexico (Chiapas) to boreal regions of Canada and Alaska (for general distribution patterns, see chapter A section 5 in Schiff et al. (2012)). The greatest recorded diversity is in western North America, with six species. However, we suspect that additional species may be discovered in Mexico and especially in southern China and Laos at high elevation in the conifer zone.

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