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


C. Taxonomic treatment

2. Xeris caudatus (Cresson)


Fig. C2.1 (female habitus)


Fig. C2.2 (male habitus)


Urocerus caudatus Cresson, 1865: 247. Holotype female (ANSP), examined by D. R. Smith (pers. comm.). Cresson, 1916: 10. Type locality: “Colorado Territory”. Norton, 1869: 363–364; Provancher, 1878: 231; Provancher, 1883: 241; Harrington, 1893: 148–149.


Sirex melancholicus; Cresson, 1880: 67 (not Westwood, 1874: 116).


Sirex caudata; Kirby, 1882: 382 (change in combination). Dalla Torre, 1894: 385; Kiaer, 1902: 407.


Xeris caudata; Ashmead, 1898: 180 (change in combination). Konow, 1898a: 74, 88; Howard, 1901: pl. 13, fig. 29; Konow, 1905b: 125, 126; Konow, 1905a: 9; Rohwer, 1912: 96 (state); MacGillivray, 1916: 171; Schiff et al. 2012: 246. 


Xeris spectrum race caudata; Bradley, 1913: 23 (change in rank). Essig, 1926: 774 ; Hedicke, 1938: 24–25 (catalog).


Xeris spectrum; Maa, 1949: 86, 170 (not Linnaeus, 1758: 560 only for Nearctic records). Burks, 1958: 17 (catalog); Middlekauff, 1960: 70; Furniss & Carolin, 1977: 454, 457; Smith, 1979: 129 (catalog); Smith & Schiff, 2002: 185; Taeger et. al., 2010: 105 (in part for Nearctic specimens; catalog).



Diagnostic combination


Among specimens with small, scattered pits between dorsoposterior edge of eye and occiput outside postocellar area and with cell C of fore wing yellowish brown [caudatus and melancholicus], most females of X. caudatus are distinguished by the sheath with basal section usually less than 0.24 times length of apical section, usually by the absence of meshes of microsculpture on laterobasal angle of cornus in dorsal view, and by abdominal tergum 9 in lateral view with meshes of microsculpture usually not well impressed, with sculpticells almost flat and somewhat scale-like on surface posterior to and above lateral furrow (the surface thus shiny). Males have a black to reddish-brown, poorly defined spot at the base of metatibia but cannot be separated from those of X. melancholicus.






Color. Head black except for small white spot on gena dorsal to middle of eye; white spot usually not extending down to genal ridge (as in Fig. B2.47); antenna black; last maxillary palpomere black. Thorax black except for white longitudinal band extending from posterolateral to anterolateral angles including vertical portion of anterior angle, the band 0.2–0.3 times as wide as lateral 0.5 of pronotum and not extending to lateral margin of pronotum (Fig. B2.59). Legs including coxae light reddish brown (coxae very narrowly black at anterior and posterior dorsal edges) (Fig. C2.1). Fore wing clear except for lightly tinted band in apical 0.25, and on posterior corner of cells 2CU and 3CU (as in Fig. B2.67); costal cell yellowish brown (possibly bleached in old specimens); most of area ventral to anal cells yellowish brown; veins black or brown (including veins C and R, and base of stigma on both sides of junction with vein 1r-rs) (as in Fig. B2.39). Abdomen black (Fig. C2.1). Sheath with apical section black and basal section reddish brown.


Head. Distance between nearest eye edge and lateral ocellus edge about 1.1–1.5 times as long as distance between inner edges of lateral ocelli (as in Fig. B2.20). Setae on clypeus 0.6–0.7 as long as diameter of a lateral ocellus (as in Fig. B2.47). Eye in lateral view (N = 20) with its maximum height 1.37–1.64 times as long as its maximum length (as in Fig. B2.47), and maximum height of eye 0.42–0.51 times as long as maximum height of head (from transverse ridge on gena above mandible to top of head) (measurements as in Fig. B2.8). Gena in dorsal view with maximum distance between outer edges clearly wider than maximum distance between outer edges of eyes (in frontal view outer edges of eyes clearly not intersecting genae) (as in Figs. B2.5 and B2.42); in lateral view with distance between outer edge of eye and genal ridge 0.48–0.61 times as long as maximum length of eye (as in Fig. B2.47, measurements as in Fig. B2.77), with almost no pits ventral to genal ridge, and with few and small to very small pits (diameter of pit 0.05–0.15 times lateral ocellus diameter) between outer edge of eye and genal ridge (mainly near eye) (as in Fig. B2.47). Transverse ridge above mandible narrow, sharp and smooth (as in B2.18). Vertex scarcely pitted, pits medium in size (pit diameter 0.2–0.3 times lateral ocellus diameter), pits present from dorsoposterior edge of eye to occiput outside postocellar area, absent on most of postocellar area; pits scattered (small specimens) to dense (large specimens) and medium in size along median furrow, a little more widespread near lateral ocelli (as in Fig. B2.42).


Thorax. Pronotum in lateral view with coarse polygonal pits on 0.1–0.7 of posterior surface (as in Fig. B2.97). Propleuron in lateral view with small pits posteriorly, each with or without tooth behind in posterior 0.5 of disc and with small polygonal pits in anterior 0.5 of disc (as in Fig. C12.7); in ventral view with scattered to moderately dense shallow small teeth with smooth surface in between (as in Fig. B2.22). Transcutal furrow of mesonotum clearly outlined  and finely sculptured, thus mesoscutum and axilla clearly distinct (Fig. C2.3). Fore wing in apical 0.3 of vein 2A not subparallel with wing edge and less abruptly curved away from wing edge and broadly curved in central section (as in Fig. C12.6); vein 3A absent (58%), reduced to a stump (37%), rarely extending slightly as a short nebulous vein (5%), but not extending along posterior margin of wing.

Abdomen. Tergum 9 in lateral view with meshes of microsculpture on ventral half below and above longitudinal furrow and posterior to it generally shallowly impressed and sculpticells flat, or slightly raised posteriorly as scales above furrow, or occasionally more distinctly scale-like (Fig. B2.93, insert); median basin with base (outlined by two lateral black longitudinal furrows) 0.8 times as wide as its median length, with maximum width of basin 1.6 times as wide as its median length and basin about 0.5 times as long medially as median length of cornus (measurements as in Fig. A3.2). Cornus constricted in dorsal view, its minimum width (at constriction) about 0.8 times as wide as maximum width subapically (as in Fig. C1.15), and its anterolateral angle generally without microsculpture meshes (Fig. B2.90, insert) or with some shallow meshes; with large teeth in apical 0.3 (as in Fig. B2.110). Sheath. Basal section 0.20–0.27 times as long as apical section (N = 90) (as in Fig. B2.89); lateral surface of apical section with well defined ridge (as in Fig. B2.13, insert); total length 1.2–1.4 times as long as fore wing length. Ovipositor. Lancet with 22–32 annuli (first 15 annuli hard to see, but still outlined; N = 9); junction of basal and apical sections of sheath aligned between 2nd–3rd annuli or occasionally 3rd annulus; major pits present on last 4–5 apical annuli before teeth annuli, and very small pit on each of the 7–15 preceding annuli (for middle and apical annuli as in Fig. C1.18).




Color. Head with dorsal spot behind eye similar in size to female. Coxae, at least metatibia (usually all tibiae) and tarsomeres 1–5 black (apical articles 3–5 or 4 and 5 sometimes brown or reddish brown in old or teneral specimens); femora completely or mainly reddish brown, and extreme base of tibiae in most specimens indistinctly outlined reddish-brown spot (trochanters, femora and tibiae as in Fig. B2.119, and tarsomeres as in Fig. B2.69).

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

Taxonomic notes


Both the North American X. caudatus and X. melancholicus have been confused with X. spectrum. The two North American species are not as closely related to X. spectrum as previously thought (Schiff et al. 2012). Their adults differ from those of X. spectrum in the color patterns of the fore wing costal cell and the base of the stigma around vein 1r-rs, and in pit size on gena between genal ridge and eye; in female by the few annuli of the ovipositor with very small pits on annuli anterior to main apical group of annuli before the teeth annuli, the color of the outer surface of coxae and, in most specimens, the color pattern of the cornus ventral surface anterior to anus; in male by the color pattern of the metatibia (and usually pro- and mesotibiae), and tarsi.


Adults of X. caudatus and X. melancholicus also differ from the similar X. pallicoxae in several structural and color character states. Females of X. pallicoxae are most similar to those of the two North American species because of the light reddish-brown coxae. Adults of the two North American species differ from X. pallicoxae by the fore wing color pattern of cell C and of the base of the stigma around the junction with vein 1r-rs and by the microsculpture of the longitudinal white band along the lateral margin of the pronotum; in females by the macrosculpture on the lateral surface of the pronotum and the propleuron; in males by the color pattern of the metatibia (usually pro- and mesotibia) and tarsi. These differences support the specific distinction of X. pallicoxae from the two North American species.


Adults of X. caudatus and X. melancholicus differ from those of X. malaisei, X. xanthoceros and X. xylocola by the color pattern of cell C of the fore wing and of the base of the stigma around the junction with vein 1r-rs; in females by the coxal and flagellum color pattern, and by the ovipositor with few annuli anterior to main apical group of annuli before the teeth annuli with a very small pit; in males by the color pattern at the base of the metatibia (and usually pro- and mesotibia) and the trochanters.


Adults of X. caudatus and X. malancholicus differ from those of X. umbra by the coarser pits on metanotum posterior to cenchrus and outer 0.5 of metascutellum, by the color pattern of cell C of the fore wing and of the base of the stigma around the junction with vein 1r-rs; in females by the leg color pattern, and by the few annuli anterior to main apical group of annuli before the teeth annuli each with a very small pit; in males by the femur color pattern.


The main challenge is distinguishing X. caudatus from X. melancholicus. The two species were not recognized at first (Schiff et al. 2012). Barcodes were the clue. Xeris caudatus is in western North America and X. melancholicus is in eastern North America. They occur sympatrically in Alberta and central Saskatchewan. The barcode results distinguish both species unequivocally. We succeeded in separating only females with moderate success using morphology. The separation is based on the relative length of the apical section of the ovipositor sheath (about 70% of specimens segregated), Despite the overlap based on two standard deviations, the ratio of basal to apical sections of the sheath were most informative when comparing averages between states, provinces and large samples within these. The average in western states and provinces varies from 0.23–0.24 whereas in the east of Saskatchewan the averages vary from 0.29–0.30. There is a clear gap at the population level and this gap supports our species level separation. In addition we found some difference in the microsculpture type on the lateral surface of tergum 9 and on the anterolateral corner of tergum 10 dorsally (base of cornus) (about 70% of specimens segregated).


Cresson’s type of Urocerus caudatus, a female from Colorado, is associated with the western species. Westwood’s type of Sirex melancholicus is a male of unknown locality in North America and has a younger name. Urocerus caudatus is the oldest name, thus X. caudatus is used for this species.

Hosts and Phenology


Xeris caudatus has a wide host range within Pinaceae (Middlekauff 1960, Cameron 1965, Morris 1967, Kirk 1975). The main hosts are firs. Based on 340 reared and confirmed specimens, the hosts are: Abies balsamea (15), A. concolor (298, Kirk, 1975), A. lasiocarpa (3, Morris 1967), Picea engelmannii, P. glauca (4), P. pungens (11), P. contorta (7), P. ponderosa, and Pseudotsuga menziesii (2) (Morris 1967).

            Based on 213 field-collected specimens, the earliest and latest capture dates are June 12 and August 18. The main flight period is from the second half of June to the first half of August with a peak in the second half of July.




Canada: Alberta, British Columbia, Saskatchewan. United States: Alaska, California, Colorado, Idaho, Montana, Oregon, South Dakota, Utah, Washingtopn, Wyoming. This is a western species, known from Alaska and Saskatchewan south to California and New Mexico (Cameron 1965) (see map C40.6 in Schiff et al. 2012).


Specimens studied: 223 females and 13 males from BDUC, BYUC, CNC, NFRC, EDUM, MTEC, OSAC, ROME, UAIC, UAM, UCRC, USFS–AK, USFS–GA, USFS–MS, and USNM.


Specimens for molecular studies: 47 specimens. See Fig. D1.2a. For each specimen the following is recorded: country, year, state/province, specimen code (in italics), and number of base pairs.


CANADA. Alberta: 2007, SIR 112, 658; 2007, SIR 113, 658; 2007, SIR 114, 658; 2007, SIR 115, 658; 2007, SIR 117, 658; 2007, SIR 118, 658; 2008, SIR 130, 658; 2008, SIR 131, 658; 2008, SIR 133, 658; 2008, SIR 136, 582; 2008, SIR 138, 658; 2008, SIR 140, 658. British Columbia. 2007, SIR 120, 658; 2008, SIR 122, 658; 2008, SIR 123, 658; 2008, SIR 126, 658; 2008, SIR 128, 658; USA. Alaska: 2010, SIR 150, 658. Colorado: 2008, CBHR 2008, 658; SIR 148, 658; 2010, SIR 149, 658. Montana: 2007, SIR 084, 657; 2010, SIR 145, 658; 2010, SIR 146, 658; 2010, SIR 147, 658. South Dakota: 2010, SIR 110, 624. Utah: 2008, CBHR 1943, 658; 2008, CBHR 1944, 658; 2008, CBHR 1945, 658. Washington: 2005, CBHR 214, 658; 2005, CBHR 229, 658; 2005, CBHR 236, 658; 2005, CBHR 236e, 658; 2005, CBHR 238, 658; 2005, CBHR 238b, 658; 2005, CBHR 238c, 658; 2005, CBHR 238d, 658; 2008, SIR 100, 612; 2008, SIR 101, 658; 2008, SIR 102, 658; 2008, SIR 103, 658; 2008, SIR 104, 658; 2008, SIR 105, 658; 2008, SIR 106, 658; 2008, SIR 107, 658; 2008, SIR 108, 658; 2008, SIR 109, 658.