ISSN 1911-2173
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

13. Xeris tarsalis (Cresson)

Fig. C13.1, (female habitus); Schiff et al. 2006: 98, 99

Fig. C13.2, (male habitus); Schiff et al. 2006: 97

Urocerus tarsalis Cresson, 1880: 52. Holotype female (ANSP), examined by D. R. Smith. Type locality: “Washington Territory”. Harrington, 1893: 148; Cresson 1916: 10.

Sirex tarsalis; Kirby, 1882: 382 (change in combination). Dalla Torre, 1894: 393.

Xeris macgillivrayi Bradley, 1913: 24, figs. 30, 35. Holotype female [published measurements suggest one specimen] (CUIC) [according to Maa (1949), but not listed by Hoebeke (1980)], not examined. Type locality: “Collected near Olympia, Washington by Mr. T. Kincaid”, as hand stamped on some copies, but no locality, number of specimens and depository given. Hedicke, 1938: 23 (catalog); Ries, 1951: 84; Middlekauff 1960: 69 (hosts). Synonymy by Maa 1949: 80, 82–83; Burks 1958: 17, Cameron, 1965: 16 (hosts); Westcott, 1971: 310 (host).

Xeris tarsalis; Maa, 1949: 82, 83 (change in combination). Burks 1958: 17 (catalog and hosts); Cameron, 1965: 16 (hosts); Westcott, 1971: 310 (hosts); Furniss & Carolin, 1977: 454, 457 (host and range); Smith 1979: 129 (catalog and hosts); Taeger et al., 2010: 105 (catalog); Schiff et al., 2012: 265.

Xeris morrisoni; synonymy by Konow, 1898a: 88 (not Cresson, 1880: 35). Bradley, 1913: 24; Hedicke, 1938: 23 (catalog); Ries, 1951: 84 (catalog); Middlekauff, 1960: 69.

Diagnostic combination

Both sexes of X. tarsalis are easily distinguished from all other Xeris species in both sexes by the narrow gena (in frontal view, the outer edges of eyes touching or slightly intersecting the genae) and by the widespread and dense pits covering almost the entire vertex, and in females by the short apical section of the sheath (the basal section of sheath is about 0.6 times as long as the apical section) and by the absence of a lateral ridge on the apical section of the sheath.



Color. Head and thorax black except for small white spot on gena dorsal to middle of eye; white spot not extending down to genal ridge (Fig. B2.6); antenna black but becoming reddish brown in apical 0.3 (Fig. C13.1); last maxillary palpomere black. Thorax black (Fig. C13.1). Legs black but becoming reddish brown at base of tibiae and apex of metatibia, and tarsi reddish brown (Fig. C13.1). Fore and hind wings darkly tinted (including cell C) (as in Fig. B2.57), veins black or brown (including veins C, R and base of stigma on both sides of junction with vein 1r-rs) (as in Fig. B2.57). Abdominal segments 2–10 and sheath reddish brown but black on tergum 1, and lateral edge of terga 2–7 and sterna 2–7 (Fig. C13.1).

Head. Distance between nearest eye and lateral ocellus edges about 0.8–1.0 times as long as distance between inner edges of lateral ocelli (Fig. C1.4). Setae on clypeus slightly 0.7 as long as diameter of a lateral ocellus (Fig. B2.6). Eye in lateral view (20 specimens measured) with its maximum height 1.21–1.37 times as long as its maximum length (Fig. B2.6), and maximum height of eye 0.52–0.60 times as long as maximum height of head (from transverse ridge on gena above mandible to top of head) (Fig. B2.6). Gena in dorsal view with maximum distance between outer edges as wide as maximum width between outer edges of eyes (Fig. B2.1) (in frontal view, outer edges of eyes touching or slightly intersecting genae) (Fig. B2.4); in lateral view with distance between outer edge of eye and genal ridge 0.42–0.64 times as long as maximum length of eye (Fig. B2.6). Gena with almost no pits ventral to genal ridge, and with many pits (diameter of pit 0.3 times lateral ocellus diameter) between outer edge of eye and genal ridge pits (Fig. B2.6). Transverse ridge near mandible narrow, sharp and mainly smooth (Fig. B2.6). Vertex densely pitted and pits large in size (diameter of pit 0.3–0.4 times lateral ocellus diameter) with almost no smooth sublateral area, and densely pitted along median gutter-like furrow (Fig. B2.1).

Thorax. Pronotum in lateral view with coarse polygonal pits outlined by sharp ridges in a reticulate pattern on 0.95 of surface (Fig. B2.15). Propleuron in lateral view with medium size polygonal pits on most of disc (as in Fig. C12.7); in ventral view with scattered to moderately dense, shallow small teeth and with clearly outlined microsculpture meshes in between (sculpticells scale-like) (Fig. B2.15). Transcutal furrow of mesonotum clearly outlined  and finely sculptured, thus mesoscutum and axilla clearly distinct (Fig. C13.3). Fore wing in middle 0.3 of vein 2A diverging very rarely slightly (as in Fig. C11.6) to usually considerably (as in Fig. C12.6) away from wing edge and then more (as in Fig. C11.6) or less (as in Fig. C12.6) abruptly curved away from wing edge; vein 3A extending toward posterior wing margin as a nebulous vein.

Abdomen. Tergum 9 with meshes of microsculpture on sublateral and dorsal surfaces shallowly outlined and sculpticells flat (surface bright), and dorsal surface outside median basin smooth (as in Fig. B2.93, insert); median basin with base (outlined by two lateral black longitudinal furrows) 0.7 times as wide as its median length, maximum width of basin 1.3 times as wide as its median length, and basin 0.6 times as long as median length of cornus (measurements as in Fig. A3.2). Cornus not constricted in dorsal view, its minimum width equal to maximum width subapically (Fig. C1.14); with large teeth in apical 0.3 (as in Fig.B2.110). Sheath. Basal section 0.6 times as long as apical section (N = 20) (Fig. B2.12); lateral surface of apical section without ridge (Fig. B2.12, insert); length 1.0–1.1 times as long as fore wing length. Ovipositor. Lancet with 35–37 annuli (all annuli clearly outlined; N = 5); junction of basal and apical sections of sheath aligned between 8th and 9th annuli, or 9th and 10th annuli; pit present and large on each of the annuli before teeth annuli, with anterior end extending to each preceding annulus as shallow furrow (Fig. B2.16).


Color. Head with dorsal spot behind eye similar in size to female. Antenna, coxae, tibiae and tarsi (except tarsomeres 3–5 or 4 and 5) black (Fig. C13.2). Abdomen reddish brown or paler on terga 2–7 or 2–8, and black on tergum 1 or 1 and 2, and on sterna 2–9 (Fig. C13.2).

Thorax. Metatibia with shallow notch on dorsal edge in basal 0.25 (Fig. C13.2).

Taxonomic notes

Females of X. tarsalis have an unusually short ovipositor. However, the most unusual feature is the presence on the ovipositor of a large pit for each annulus from annulus 2 up to the teeth annuli. In all other species of Xeris, the ovipositor is smooth except for a few small pits near the apex or an extremely small pit on one or more annuli anterior to the typical apical group of pits. This structural difference may reflect a different life style. For example, the common X. caudatus has small mycangia, but no fungus in them (Schiff et al. 2012). Larvae of X. caudatus probably survive on fungi brought by other Siricidae, as observed by Fukuda et al. (1997) with X. malaisei in Japan. When considering that the main hosts all belonging to the Cupressaceae, a family almost never used by North American Xeris, it would not surprise us if females of X. tarsalis might be able to carry fungal oidea in their mycangia.

Hosts and phenology

Xeris tarsalis has a moderate host range (Middlekauff 1960, Cameron 1965,Westcott 1971). Based on 138 reared and confirmed specimens, all host are Cupressaceae: Cupressus macrocarpa (131), Juniperus sp. (2), J. occidentalis (3) [from scorched trees (Westcott 1998)], Calocedrus decurrens (5), and Thuja plicata.

Based on 108 field-collected specimens, the earliest and latest capture dates are early March to early October. The main flight period is from early July to early October with a peak from early September to early October.


United States:California (Middlekauff, 1960), Oregon, South Carolina (probably not established), Washington. Xeris tarsalis is known from the Cascade Mountains and Sierra Nevada west to the Pacific coast (Cameron 1965, Smith 1979) (see map C41.3 in Schiff et al. 2012). One female was collected emerging from wood in South Carolina, and we have seen a female (FRNZ) intercepted in Auckland, New Zealand.

Specimens studied and included for the distribution map: 67 females and 77 males from CUCC, OSAC and USNM.