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Siricidae (Hymenoptera: Symphyta: Siricoidea) of the Western Hemisphere
CJAI 21, July, 2012
doi: 10.3752/cjai.2012.21
Nathan M. Schiff, Henri Goulet, David R. Smith, Caroline Boudreault, A. Dan Wilson, and Brian E. Scheffler

Xeris tarsalis (Cresson)

Fig. C45.1, Schiff et al. 2006: 98, 99 (female habitus)
Fig. C45.2, Schiff et al. 2006: 97 (male habitus)
Fig. C41.3 (map)

Urocerus tarsalis Cresson, 1880: 52. Holotype female (ANSP), examined by DRS. Cresson 1916: 10. Type locality: “Washington Territory”.
Sirex tarsalis; Kirby, 1882: 382 (change in combination).
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. Middlekauff 1960: 69. Synonym by Maa 1949: 82; accepted by Burks 1958: 17, Smith 1979: 129. Type locality: “near Olympia, Washington”, as hand stamped in some copies, but no locality, number of specimens and depository given.
Xeris tarsalis; Maa, 1949: 82 (change in combination); accepted by Burks 1958: 17, Smith 1979: 129.
Xeris morrisoni; synonym by Konow 1898: 88 (not Cresson, 1880: 35) accepted by Ries, 1951: 84.

Diagnostic Combination

Both sexes of X. tarsalis are easily recognized by the narrow gena (in frontal view, the outer edges of eyes touch or slightly intersect the genae), and the widespread and dense pits covering almost all the dorsal surface of the head and gena ventral to the genal ridge. Females have a quite short apical section of the sheath (basal section of sheath about 0.6 times apical section), no ridge on the apical section of the sheath, and a broad and not constricted cornus in dorsal view.



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. B5.5); antenna black but shifting to reddish brown in apical 0.3. Thorax black. Legs black but reddish brown at apex of metatibia, and tarsi (Fig. C45.1). Fore and hind wings darkly tinted (including C cell), veins black (including veins C and R, and vein 1r-rs near junction with stigma). Abdomen segments 2–10 and sheath reddish brown but black on tergum 1, and lateral edge of terga 2-7 and sterna 2–7.

Head. Eye in lateral view (20 specimens measured) with maximum height 1.21–1.37 times as long as maximum length (Fig. B5.5), 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. B5.5). Gena in dorsal view with maximum distance between outer edges as wide as maximum width between outer edges of eyes (in frontal view, outer edges of eyes touching or slightly intersecting genae) (Fig. B5.3), and in lateral view distance between outer edge of eye and genal ridge 0.42–0.64 times as long as maximum length of eye (Fig. B5.5). Transverse ridge near mandible narrow, sharp and mainly smooth (as in Fig. B5.21). Head in dorsal view with pits dense but sometimes narrowly absent submedially (as in Fig. B5.21); pits quite numerous between eye and genal ridge, and not extending below ventral level of eye and genal ridge (thus separated by smooth area from pitted surface of occiput) (Fig. B5.5).

Thorax. Fore wing vein 3A extending toward posterior wing margin as a nebulous vein.

Abdomen. Median basin of tergum 9 with base (outlined by two lateral black longitudinal furrows) 0.7 times as wide as median length, maximum width of basin 1.2 times as wide as median length, and basin 0.6 times as long as median length of cornus (Fig. C45.3). Cornus not constricted in dorsal view, its minimum width (where constriction normally seen in other species of Xeris) equal to maximum width subapically (Fig. C45.3). Sheath. Length about as long as length of fore wing; basal section 0.6 times as long as apical section (Fig. B5.11); lateral surface of apical section without longitudinal ridge (Fig. B5.11 insert). Ovipositor. Lancet with 35–37 annuli (all annuli clearly outlined); junction of basal and apical sections of sheath aligned between 8th and 9th, or 9th and 10th annuli; pits present on all annuli before teeth annuli and large, with anterior end extending to preceding annulus as shallow furrow (Fig. B5.14).


Color. Antenna, tibiae and tarsi (except tarsomeres 3–5 or 4 and 5) black. 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.

Thorax. Metatibia with shallow notch along dorsal edge in basal 0.25.

Taxonomic Notes

Females of X. tarsalis are unusual, with a rather short ovipositor. However, the most unusual feature is the presence of large pits along the entire length of the ovipositor. In all other species of Xeris, the ovipositor is smooth except for a few small pits near the apex. This structural difference may reflect a different life style. For example, the common X. caudatus has mycangia, but NMS confirmed the absence of fungus in them. Their larvae probably survive on fungi brought by other Siricidae, as observed by Fukuda and Hijii (1997) with X. malaisei in Japan (X. spectrum in their publication). However, we suspect that females of X. tarsalis may carry a fungus in its mycangia.

Hosts and Phenology

Xeris tarsalis has a wide host range (Middlekauff 1960, 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.


USA: CA (Middlekauff), OR, SC (probably not established), WA. Xeris tarsalis is known from the Cascade Mountains and Sierra Nevada west to the Pacific coast (Cameron 1965, Smith 1979) (Fig. C41.3). One female was intercepted 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.