Fig. C39.1 (live female)
Both sexes of Xeris are easily recognized by the small vertical ridge on the gena posterior to the eye, the metatibia with one spur, and the hind wing without an anal cell.
Color. Black portions of body without metallic reflections.
Head. Antennal sockets with distance between their inner edges 1.5–2.0 times distance between outer edge of socket and nearest edge of eye (Fig. B5.4). Distance between inner edges of lateral ocelli 0.5–1.2 times as long as distance between outer edge of lateral ocellus and nearest inner edge of eye (Figs. B5.3 & B5.4). MMaximum distance between outer edges of eyes either less than maximum width of head (thus, in frontal view, genal edges completely visible and not intersected by outer edges of eyes) (Fig. B5.4) or as long as maximum width of head (thus, in frontal view, genal edges intersected by outer edges of eyes) (Fig. B5.3). Minimum distance between inner edges of eyes about 1.6 times as long as maximum eye height (Fig. B5.4). Gena with ridge behind eye, with white spot almost always in dorsal half (Fig. B1.41), 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; in female apical 5–10 flagellomeres with sensory oval impressions on dorsal and ventral surfaces, in male only with ventral sensory oval impressions; in female middle and apical flagellomeres with sensory pits over most surfaces except outer surface, in male sensory pits present over inner surface and a small section of outer surface.
Thorax. Pronotum smooth on anterior vertical surface. Mesoscutum densely pitted only over median 0.5–0.7. Mesotarsomere 1 in lateral view not enlarged, its dorsal and ventral edges almost parallel, and base of tarsomere 0.7 or less its maximum width. Metatibia in male in lateral view 5.5–9.0 times as long as maximum width. In female metatarsomere 2 in lateral view with dorsal edge 4.0–6.0 times as long as maximum height. Metatarsomere 5 0.5–0.7 as long as metatarsomere 2 (Fig. B5.51). Fore wing with apex acutely and angularly rounded, with vein 2r–m present and joined to cell 2M (as in Fig. B1.71), with vein 2r-m, 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 (as in Fig. B1.25), without vein Cu1, with vein 1cu–a joining vein Cu close to M, and with vein 3A well developed, stump-like or absent. Hind wing with hamuli clearly present basal and apical to junction of veins R1 and C (as in Fig. B1.11), and without anal cell.
Abdomen. Female. Cornus in dorsal view long, narrow, and lateral edges either not constricted or constricted near middle (Fig. C39.2). Tergum 9 with median basin with lateral edges markedly divergent, straight then rounded near lateral angle, and sharply outlined for about 0.5 times 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. C39.2). Cercus present but very small. Sheath. Length of basal section 0.2–0.5 as long as apical section (Figs. B5.11, B5.12 & B5.13); apical section with lateral surface sharply folded except at very base and apex (Fig. B5.13, insert), or not folded (in one species, X. tarsalis), and without teeth in apical third of dorsal margin (Fig. B 5.11, insert). 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 with shallow, long and open ended pit (Fig. B5.15); for most species annuli 4–6 anterior to teeth annuli with medium pit and pits decreasing in size anteriorly in following 3–5 annuli, and following annuli without pit or with very small pit present from anterior annulus to as many annuli as starting at annulus 2, or in one species, X. tarsalis, with many large pits starting at annulus 2 up to teeth annuli (Fig. B5.14); edge of last 5 to 7 annuli before teeth annuli ventral to pit sharply and acutely produced, and edge of last 7 to 14 annuli before teeth annuli extended as a sharp ridge to ventral edge of lancet.
Neoxeris melanocephala M.S. Saini and D. Singh, based on three females, is a typical species of genus Xeris. The eye proportions (1.25 as high as long) are the same as for all Xeris specimens we examined (range 1.18–1.63, based on 62 specimens and 5 species). The lack of a white spot on the gena in females is not a good criterion for a genus level classification. For example, 30 females examined of X. himalayensis (Bradley) from India and Pakistan showed a complete range from a large white spot to no spot on the gena, and we have seen a few specimens of Xeris melancholicus and X. spectrum with a completely black head. The ovipositor of N. melanocephala near the apex is typical of almost all Xeris, except X. tarsalis. Other described character states are typical of females of most Xeris species. We suspect that N. melanocephala is simply a dark color form of X. hymalayensis. The only significant difference in the description is the reddish brown apical section of the flagellum. This color pattern is seen occasionally in specimens with black flagellum. The Indian species is therefore transferred to Xeris as X. melanocephalus (M.S. Saini and D. Singh), new combination.
The gender of Xeris is questionable. The name of its type species, Ichneumon spectrum, is a noun. In the latest catalog (Taeger et al. 2010) it is treated as masculine in X. morrisoni indecisus, and as feminine in X. indiana, the latter being an inadvertent misspelling of Saini et al. (2006). (Stephen Blank, pers. comm.). Xeris as a classical name means a kind of plant (Bradley 1913). This name does not make sense. Costa (1894) does not give the origin of the generic epithet, but very likely it is a palindrome of the name Sirex. We follow Maa (1949) and consider Xeris as masculine.
Not much has been published on the biology of Xeris species. The European X. spectrum (and the Japanese population of this species) is close to but clearly distinct from the North American X. caudatus and X. melancholicus. Because we have no information about any Neartic species of Xeris, we present biological information of X. spectrum under the genus heading.
The most interesting feature of X. spectrum and also X. caudatus is that females do not carry symbiotic fungus in their mycangia (Francke-Grosmann 1939, Fukuda and Hijii 1997, confirmed by NMS). The question is therefore what do larvae eat during their development? Females of most species of Siricidae carry arthrospores of Amylostereum spp., a genus of basidiomycete fungi. During oviposition the fungus is deposited on each egg placed in the sap wood. The fungus produces an enzyme to decompose the wood cellulose or lignin, changing it to a form that can be assimilated by the larvae and making larval development possible. Fukuda and Hijii (1997) clearly showed that larvae of X. spectrum in Japan develop only if the A. chailletii or A. areolatum are present at the oviposition site. Both species of fungi are equally accepted by Xeris larvae. Fukuda and Hijii’s observations confirm earlier observations in Europe that X. spectrum females often deposit their eggs in trees already infested with Sirex and Urocerus spp. (Francke-Grosmann 1954). Moreover, the emergence holes of X. spectrum in Japan are in close proximity to those of other horntails. This suggests that females of Xeris are attracted by odors emitted by Amylostereum fungi inoculated by other fungus carrying horntails.
Xeris spectrum in Japan shows two periods of emergences, one in spring and one in summer (Fukuda and Hijii 1997). We have no evidence of a similar pattern with the Nearctic X. caudatus. The spring oviposition cycle offers Xeris spectrum larvae a very viable fungus but more competition with other horntail larvae, whereas a summer oviposition cycle offers the Xeris larvae a less viable fungus with less competition from other horntail larvae.
Xeris is a moderate sized genus with 10 species and subspecies. Three species are recorded from Eurasia (Taeger and Blank 2011, Tager et al. 2010). All are in the northern hemisphere. In the New World, seven endemic species are known. They are recorded from southern Mexico to boreal regions of Canada and Alaska. The greatest diversity is in western North America.
The 7 species treated are: