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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 caudatus (Cresson), sp. rev.

Fig. C40.1 (female habitus)
Fig. C40.2 (male habitus)
Fig. C40.6 (map)

Urocerus caudatus Cresson, 1865b: 247. Holotype female (ANSP), examined by DRS. Cresson 1916: 10. Type locality: Colorado Territory.
Sirex caudata; Kirby, 1882: 382 (combination).
Xeris caudata; Ashmead, 1898: 180 (combination).
Xeris spectrum race caudata; Bradley 1913: 23 (change in combination and rank).
Xeris spectrum; Maa, 1949: 86 (not Linnaeus, 1758: 560). Burks 1958: 17, Smith and Schiff 2002: 185.
Xeris spectrum spectrum; Maa, 1949: 86 (status); accepted by Burks 1958: 17, Middlekauff 1960: 70 (in part), Burks 1958: 17, Smith 1979: 129.

Diagnostic Combination

Among specimens with a marginal longitudinal band on the pronotum and with short setae on the head  [melancholicus], both sexes of X. caudatus are recognized by the very small pits (pit diameter 0.05–0.15 times lateral ocellus diameter) on the gena between the upper and lower limits of the genal ridge, and the small white spot that usually does not extend to the genal ridge. Females also have completely light reddish brown coxae (except the black anterior and posterior dorsal edges), and generally longer apical section of the sheath (basal section/apical section ratio less than 0.25 for most specimens). Males of caudatus cannot be separated from males of 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. B5.41); antenna black. Thorax black except for white longitudinal band extending from posterolateral to anterolateral angles including vertical portion of anterior angle (as in Fig. C43.3). Legs including coxae light reddish brown (coxae black on anterior and posterior dorsal edges) (Fig. C40.1). Fore wing clear except for lightly tinted band before stigma, in apical 0.25, and in cell 2CU; costal cell brown and most of area ventral to anal cells yellowish brown; veins black (including veins C, R and stigma on both sides of junction with vein 1r-rs) (as in Fig. B5.17). Abdomen black. Sheath with apical section black and basal section reddish brown.

Head. Eye in lateral view (20 specimens measured) with maximum height 1.37–1.64 times as long as maximum length (as in Fig. B5.43), 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) (as in Fig. B5.7). 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 Fig. B5.4), and in lateral view distance between outer edge of eye and genal ridge 0.48–0.61 times as long as maximum length of eye (as in Fig. B5.27). Transverse ridge above mandible narrow, sharp and mainly smooth (as in Fig. B5.21). Head in dorsal view with pits restricted to vertex (scarcely pitted from dorsoposterior edge of eye to occiput) and postocellar area (scattered or absent on most of median furrow, but a little more widespread near lateral ocelli) (as in Fig. B5.2), in lateral view almost absent on gena ventral to genal ridge, and few and small (diameter of pit 0.1–0.2 times lateral ocellus diameter) between outer edge of eye and genal ridge (mainly near eye) (as in Fig. B5.43).

Thorax. Fore wing vein 3A absent (58%), reduced to a stump (37%), rarely extending slightly as a nebulous vein (5%), but not extending along posterior margin of wing.

Abdomen. Median basin of tergum 9 with base (outlined by two lateral black longitudinal furrows) 0.8 times as wide as median length, with maximum width of basin 1.6 times as wide as median length and basin about 0.5 times as long medially as median length of cornus (as in Fig. C39.2). Cornus constricted in dorsal view, its minimum width (at constriction) 0.8 times as wide as maximum width subapically (as in Fig. C39.2). Sheath. Length 1.2–1.4 times as long as fore wing length; basal section 0.20–0.27 times as long as apical section (Fig. C40.3); lateral surface of apical section with well defined ridge (as in Fig. B5.13, insert). Ovipositor. Lancet with 22–32 annuli (first 15 annuli hard to see, but still outlined; N=9) (as in Fig. B5.15); junction of basal and apical sections of sheath aligned between 2nd and 3rd, or occasionally 3rd annuli; medium pits present on last 4-5 apical annuli before teeth annuli, and very small pit on 7–15 preceding annuli (as in Fig. B5.15).


Color. Coxae, tibiae (except very base) and tarsomeres 1–5 black (apical articles sometimes brown or reddish brown in old or teneral specimens); femora completely or mainly, and extreme base of tibiae (not sharply outlined but gradual shift) reddish brown (as in Fig. B5.51).

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

Taxonomic Notes

In the Old World, five species and subspecies of Xeris are recorded (Taeger and Black 2011, Taeger et al. 2010): X. spectrum cobosi Viedma and Suarez (1961), X. himalayensis Bradley 1934, X. indianus Vasu and Saini (1999), X. spectrum (Linnaeus 1758) and X. spectrum malaisei Maa (1949). We also include X. melanocephalus (Saini and Singh 1987, Taeger et al., 2010). In previous works, X. caudatus was known as Xeris spectrum spectrum (Maa 1949, Smith 1978 & 1979, Smith & Schiff 2002, Schiff et al. 2006). We have seen the types of all the above taxa except X. indianus and X. melanocephalus. The North American specimens of X. caudatus are rather similar in many character states to many specimens of the European Xeris spectrum and to the types of the Asiatic X. spectrum malaisei. Xeris spectrum malaisei differs in many character states from American specimens and from X. spectrum spectrum. We recognize X. caudatus as specifically distinct from both subspecies of X. spectrum. All studied specimens of the X. spectrum complex consists of the subspecies of X. spectrum, X. caudatus, and  X. melancholicus; the complex is recognized by the well developed longitudinal band on each side of the pronotum in dorsal view and the low density of pits on each side of the postocellar area. However, there are differences between the Eurasian species of the complex and the North American specimens. A revision of Xeris is ongoing, so we discuss here only the currently described taxa of the complex.

Based on color pattern, females of the transpalaearctic X. spectrum with dark coxae and males with reddish brown apical 0.15–0.2 of metatarsomere 1 are easily distinguished from females and males of X. caudatus. We studied 135 specimens of X. spectrum and the females match the Linnean type of X. spectrum (Linnaeus).

The holotype female of Xeris spectrum malaisei Maa is distinguished from females of X. caudatus by a narrow head, black coxae and femora, and reddish brown flagellum in apical 0.2–0.3.

X. himalayensis and X. cobosi, the third and fourth Euroasiatic species studied by us (38 specimens seen), are not particularly close to X. caudatus. In these two species, the pronotum has no white longitudinal band, pits are more abundant (denser) and larger on the vertex and the space between the genal ridge and the eye (quite similar to those of X. indecisus or X. morrisoni), in females the genal spot is small to absent, and in males (only known for X. himalayensis) the spot is very large and tarsomeres 3–5 are reddish brown.

In summary, the North American X. caudatus is distinct from all named Old World Xeris on structure and color pattern in both sexes. We have not seen specimens of X. caudatus from temperate and boreal Asia. The nearest Asiatic populations studied are from Japan and China and the Russian Far East. They are also very distinctive in color pattern from X. caudatus (including specimens from Alaska). Thus, there is no evidence that X. caudatus has a Holarctic range. Our morphological data supports our decision to classify X. caudatus as specifically distinct from any of the Eurasian X. spectrum species complex. Our DNA barcoding results support this conclusion.

Despite the above clarifications, there is still a problem associated with X. caudatus. The barcodes of specimens from eastern North America differ by 3.5% from the barcodes of specimens from western Washington (three specimens only). More specimens studied for these two forms confirmed the above difference. A study based on females from the western states and provinces (western Alberta and central and southern British Columbia) and samples from eastern Alberta to Nova Scotia show a different trend in the ratio of the length of the basal and apical sections of the sheath. In the western population, the apical section of the sheath is generally longer relative to the basal section. For 73 females from the western states and provinces, the relation between the basal section and the apical section shows a lower mean = 0.237 (one standard deviation = 0.015) and for 42 females in the East (e.g., Saskatchewan to Nova Scotia), the relation between the basal section and the apical section shows a higher mean = 0.296 (one standard deviation = 0.030). The differences between the means of the two samples are 1.25 standard deviations apart. Basically, 75% of specimens could be distinguished if the ratio is smaller than 0.25 for the western unit (specimens from Alaska, British Columbia, Alberta and southward including western South Dakota) or greater than 0.27 for the transcontinental unit (specimens Alberta and eastward). Specimens with values between 0.25 and 0.27 are of uncertain status. Moreover, in Alberta both populations exist sympatrically. Therefore, we consider the two units as specifically distinct.

Two names apply to the North American units, Sirex melancholicus Westwood and Urocerus caudatus Cresson. The female holotype of U. caudatus is from Colorado and matches the western species. It is the oldest name.

Hosts an 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 concolor (298, Kirk, 1975), Picea engelmannii, and Pinus ponderosa. Other hosts are Abies balsamea (15), A. concolor, A. lasiocarpa (3, Morris 1967), Picea engelmannii, P. glauca (4), P. pungens (11), P. contorta (7), P. ponderosa, and Pseudostuga 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: AB, BC (Cascades eastern slope and eastward), SK. USA: AK, CA, CO, ID, MT, OR, SD, UT, WA, WY. Xeris caudatus, a western species, is known from Alaska, British Columbia, and Alberta south to California and New Mexico (Cameron 1965) (Fig. C40.6).

Specimens studied and included for the distribution map: 237 females and 13 males from, BYUC, CNC, MTEC, OSAC, UAIC, UAM, UCRC, USFS–GA, USFS–MS, and USNM.

Specimens for molecular studies: 14 specimens. See Fig. E2.3.

CANADA. Alberta: 2008, CNCS 1090, 587. USA. Colorado: 2010, CBHR 2008, 658. Montana: 2007, CNCS 1084, 654. 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.