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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

Sirex nitidus (T. W. Harris), comb n. and sp. rev.

Fig. C13.1 (female with pale femora, habitus)
Fig. C13.2 (female with dark femora, habitus)
Fig. C13.3 (male with pale femora and dark abdominal apex, habitus)
Fig. C13.4 (male with pale femora and light abdominal apex, habitus)
Fig. C13.5 (male with black femora and light abdominal apex, habitus)
Fig. C13.6 (male with black femora and black abdomen, habitus)
Fig. C3.1 (live female with pale femora)
Fig. C13.8 (map)

Urocerus nitidus T. W. Harris, 1841: 391. Holotype female (MCZC) with abdomen missing, examined by DRS and image examined by HG. Type locality: Massachusetts.
Sirex juvencus juvencus Smith, 1979: 127 (not Linnaeus, 1758: 560).
Sirex juvencus cyaneus Bradley, 1913: 14 (not Fabricius, 1781: 419).
Sirex cyaneus Ries, 1951: 83 (not Fabricius 1781: 419); Smith, 1979: 126.
Sirex californicus Bradley, 1913: 14 (not Ashmead, 1904: 64); Ries 1951: 83, Middlekauff 1960: 62. This misidentification applies only to pale legged females of S. californicus.

Diagnostic Combination

Specimens with reddish brown femora. Among females with black abdomen, completely light reddish brown tibiae, and a long tarsal pad (pad length 0.7–0.8 as long as ventral length of tarsomere) [cyaneus, abietinus], those of S. nitidus are recognized by the larger pits at the middle of the lancet (length 0.18–0.25 times as long as length of annulus). Among males with mainly black metatibia and with net-like pits on median 0.5-0.7 of mesoscutum [abietinus, cyaneus, and varipes], those of S. nitidus are recognized by the black or brown spot on at least part of the dorsal surface of the mesotibia and mesotarsomere 1 (it may include mesotarsomeres 2 and 3), the generally fine pits on the gena and vertex (diameter of pit 0.1–0.2 that of lateral ocellus), and the narrow pale base of the metatibia (only the area of minimum constriction reddish brown).

Specimens with black or mainly black femora (AK, YT, northern BC and northern half of AB). Females of S. nitidus are recognized by the long tarsal pad (length 0.7–0.8 times ventral length of tarsomere), short metatarsomere 2 (2.0–3.0 times as long as high), dark blue abdomen, and larger pits at the middle of the lancet (length 0.18–0.25 times length of annulus). Males of S. nitidus are recognized by the light reddish brown protibia and protarsus, moderately fine pits on the head, and narrow light reddish brown transverse band at the base of the metatibia.



Color. Body, antenna (less than 1% of specimens with flagellomeres 1 or 1 and 2 brown; only one specimen with flagellomeres 1–4 light reddish brown), and palps black with dark blue metallic reflections. Coxae black, femora (except brown base), tibiae and tarsi (apical half of metatarsomeres 5 usually darker but not dark brown or black) light reddish brown (Fig. B2.2), or in Alaska, Yukon and northern British Columbia and northern Alberta some specimens with metafemur black (usually pro– and mesofemur also, and in some specimens the dorsal surface of the metatibia black as in S. varipes and in one specimen the tibiae and tarsi are completely black). Fore wing mainly clear, at most light yellowish brown behind stigma (Fig. B2.75).

Head. Gena with pits 2.0–4.0 pit diameters apart and mainly absent centrally behind eye (Fig. B2.56), vertex and postocellar area with pits 2.0–4.0 pit diameters apart (Fig. B2.62), and each pit diameter about 0.1–0.2 that of lateral ocellus.

Thorax. Mesoscutum with coarse, net-like pits over most of median surface (Fig. B2.65). Metatarsomere 2 in lateral view 2.0–2.2 times as long as high, and its length about 1.0–1.1 times length of tarsomeres 3 + 4) (Fig. B2.60); tarsal pad 0.7–0.9 times as long as ventral length of tarsomere (Fig. B2.67). Fore wing vein 3A absent (Fig. B2.75).

Abdomen. Median basin of tergum 9 with basal width 0.9–1.1 times as long as median length, maximum width 1.3–1.4 times as long as median length, and median length 0.5–0.6 times as long as cornus length (as in Fig. B2.88). Cornus in dorsal view quite short, with edges straight, its median length 1.0–1.2 as long as maximum width of abdomen at junction of terga 9 and 10 (as in Fig. B2.88). Sheath. Length 0.65–0.8 times fore wing length, basal section 0.91–1.17 times as long as length of apical section (Fig. A3.26). Ovipositor. Lancet with 29–35 annuli (basal annuli clearly outlined); junction of basal and apical section of sheath aligned between 10th and 11th or 11th and 12th annuli, with 25–30 pits beginning with annulus 2. Pits near middle annuli or area at base of apical section of sheath, 0.18–0.3 times as long as an annulus (pits gradually and markedly decreasing in size toward base (Fig. B2.83)), 0.4–0.6 times as high as lancet height in lateral view, and about 1.1–1.4 times as long as high (Fig. B2.83); annulus 10 length/ovipositor diameter (lance + lancet) 1.29–1.81 (based on 32 specimens). Last three annuli before teeth annuli as well as first tooth annulus with ridge on ventral edge of pit (Fig. C13.7). Edge of apical 5-6 annuli before teeth annuli extending as ridge to ventral edge of lancet.


Color. Head, thorax and coxae black with dark blue metallic reflections. Pale form with coxae, mesotibia (part of dorsal surface), mesotarsomere 1 (often mesotarsomere 2) (Fig. B2.135), metatibia (except extreme base), and metatarsomeres 1–3 black; femora, protibia and protarsus, most of mesotibia, mesotarsomeres 2–5, base of metatibia (spot extended slightly beyond minimum constricted portion and about as long as wide (Fig. B2.91)), ventral and part of dorsal surfaces of mesotarsomere 1, and metatarsomeres 4 and 5 light reddish brown (Fig. B2.135). Black form (from Alaska commonly, and Yukon to Newfoundland occasionally) with at least metafemur (pro- and mesofemur ranging from partly to completely black) black. Fore wing clear, lightly yellowish brown in apical 0.25. Abdomen segments 1 and 2 or 1–3 black (rarely abdomen completely black, and a few specimens with intermediate pattern seen); segments 3–9 or 4–9 light reddish brown (dominant pattern in the Prairies and western regions) (Fig. B2.140), or segments 3–7 or 4–7 light reddish brown and segment 8 (including sternum 9) black (common pattern east of the Prairie region) (Fig. B2.139).

Thorax. Metatibia 3.8–4.3 times as long as maximum width (Fig. B2.91). Metatarsomere 1 in lateral view 2.7–3.4 times as long as maximum height.

Taxonomic Notes

One type female of Urocerus nitidus exists, but the abdomen (and, therefore, the ovipositor, which has the only diagnostic characters) is missing so this type specimen cannot be assigned unequivocally to this species. The type is from a region in eastern North America where both Picea and Abies occur. Therefore, based on the type locality, the holotype could be either the species associated with Picea, or the species associated with Abies, namely S. cyaneus. We decided to assign the T. W. Harris name, S. nitidus, to the species associated with Picea, rather than describing it as new.

Specimens of S. nitidus, as well as those of S. varipes, S. abietinus, S. cyaneus, and pale specimens of S. californicus, have been variously assigned to S. juvencus or S. cyaneus (Essig 1926, Bedard 1938, Middlekauff 1960, Cameron 1965, Morris 1967). Published information is not meaningful without voucher specimens.

Both sexes of S. nitidus differ from those of the European S. juvencus. Females of S. nitidus have the five basal flagellomeres almost always (99%) black or brown (light reddish brown in S. juvencus), the most basal annuli (2 or 3) of the ovipositor have very small pits relative to those near the middle (quite similar in size at the base and the middle in S. juvencus), and the junction of the basal and apical sections of the sheath is aligned between the 10th and 11th annuli of the ovipositor (between the 12th and 13th annuli in S. juvencus) (Viitasaari 1984, Viitasaari and Midtgaard 1989). Almost all males of S. nitidus have a brown or black spot on the dorsal surface of the mesotibia, and/or a brown spot on mesotarsomere 1 or 1 and 2 (completely light reddish brown in S. juvencus). Therefore, S. nitidus is specifically distinct from S. juvencus. Sirex juvencus is only known from interceptions at American and Canadian ports but has not established in North America because in most ports its host plants, Picea spp., are absent.

Sirex nitidus is very similar to the European S. torvus M. Harris, known as S. cyaneus in Europe (see “taxonomic notes” under S. cyaneus and Chapter D. Additional Notes). Sirex torvus is found in central Europe. Females share the same type of ovipositor and color pattern and are almost undistinguishable from S. nitidus. However, in S. nitidus, the gena is clearly pitted and the pits are scattered, but in S. torvus the pits are few and very fine. In addition, we compared the distances between lancet annuli 2, 5 and 10 relative to the ovipositor diameter of S. nitidus (32 females from Laniel, Quebec) against the same measurements taken from Viitasaari and Midtgaard (1989) based on 5 females of S. torvus. In females of S. nitidus the annulus length/ovipositor diameter (lance + lancet) for annulus 2 is 2.0–2.7 (mean = 2.3) [2.6–2.7 (mean = 2.65) in S. torvus], for annulus 5 1.5–2.2 (mean = 1.9) [2.25–2.35 (mean = 2.3) in S. torvus], and for annulus 10 1.3–1.8 (mean = 1.5) [values not available in Viitasaari and Midtgaard, (1989) for S. torvus]. We measured 26 specimens of S. torvus for the above parameters of annulus 10, and the values vary from 1.39–1.90. Except for a small difference in annulus 5 between the two species there were no differences in the other proportions. Males of S. nitidus have the mid leg (except for males from Alaska) usually less darkly colored (mesotibia and/or mesotarsomere 1 each with a brown or black spot on the dorsal surface) [more darkly coloured in S. torvus: most of the mesotibia dorsal, lateral and most or all of ventral surface and almost all of mesotarsomere 1 black]. In eastern North America, the apex of the abdomen of most specimens of S. nitidus is black whereas the apex is reddish brown westward (apex of abdomen is completely reddish brown in S. torvus). Sirex nitidus is close to S. torvus, but is not exactly the same. The main hosts of S. torvus are Abies spp., but for S. nitidus are Picea spp. The differences in color pattern of the middle leg, the geographical change in color of the apex of the abdomen, and the differences in host preferences preclude an accidental introduction of S. torvus into North America. Because of differences in genal pits size and density, color pattern in males and host preferences, we recognize S. nitidus as specifically distinct from the S. torvus.

Sirex nitidus is also very similar to the little known European species, S. atricornis Kjellander. The species is subarctic in northern Scandinavia, Finland and Russia. It may extend to eastern Russia. In Scandinavia, the larvae of this species probably develop only on Pinus spp. as no other conifers are recorded from that region of northern Europe. The only difference seen in the two females (DABH) of S. atricornis studied by Viitasaari (1984) is the shape of the second annulus before the apical teeth annuli. The ridge of this annulus is straight in S. atricornis (very slightly curved in S. nitidus). This very subtle difference may vary geographically. Females of S. nitidus have wings that are lightly darkened near middle and apical 0.25 (completely clear in S. atricornis). In addition, we compared the distances between lancet annuli 2, 5 and 10 relative to the ovipositor diameter of each annulus (32 females from Laniel, Quebec) of S. nitidus against the same measurements based on 15 females of S. atricornis studied by Viitasaari and Midtgaard (1989). In females of S. nitidus the annulus length/ovipositor diameter (lance + lancet) for annulus 2 is 2.0–2.7 (mean = 2.3) [2.5–2.6 (mean = 2.55) in S. torvus], for annulus 5 1.5–2.2 (mean = 1.9) [2.1–2.2 (mean = 2.15) in S. atricornis], and for annulus 10 1.3–1.8 (mean = 1.5) [values not available for S. atricornis]. The S. atricornis proportions are within the range of the S. nitidus proportions, but the means for S. nitidus are clearly lower than those for S. atricornis. It seems that the coefficient of variation is much lower for S. atricornis than for S. nitidus (8% and 9% in the latter). At this point, we do not see any difference between S. nitidus and S. atricornis. As pointed out by Viitasaari and Midtgaard (1989), S. atricornis may be part of a species complex in the Palaearctic. We think that S. torvus and S. nitidus are also part of this complex.

In North America, females of S. nitidus may be confused with North American S. cyaneus and S. abietinus females. They are distinguished from the latter two species by a pit on annulus 2. Females of S. nitidus may be confused with S. noctilio and the pale legged form of S. californicus. They are distinguished from the latter two species by the length of the tarsal pad on metatarsomere 2, and pit development on the vertex and ovipositor.

Geographical Variation

Adults of S. nitidus show great variation in color pattern. The patterns are not random but change along geographical lines. Specimens with intermediate color patterns have been seen. Therefore, the color forms are not discrete. The most striking variation is in femur color. Femora may be black or light reddish brown. The pale femora pattern is seen in all regions, but females with black femora are centered in Alaska and are recorded from northernmost British Columbia, Yukon, and as far south as central Alberta. In males the pattern is similar but a few males with black femora have been recorded across Canada as far as Newfoundland in the boreal zones. The black femora form is not recorded in the southern boreal zone and further south. The next significant character in males is the color pattern at the apex of the abdomen. The apical segments may vary from black to reddish brown. From Manitoba and westward the apex is completely reddish brown. From Manitoba and eastward, most specimens have a black abdominal apex. A rare color variation is recorded in males with completely black abdomen in southern Yukon, and northernmost and southern British Columbia. All the above color variation patterns change gradually and subspecific segregation is not justifiable.

Hosts and Phenology

Long series of carefully reared and identified specimens of S. nitidus are mainly from Picea spp. (88%). A few specimens were associated with Abies, Larix, Pseudotsuga, Tsuga, Pinus and Thuja. Based on 253 reared and confirmed specimens all but one hosts are Pinaceae: Abies balsamea (14) (Johnson 1930 – no voucher specimens seen, they could be S. cyaneus), A. lasiocarpa (2), Larix laricina (7), Picea sp. (2), P. engelmannii (34), P. glauca (107) (reported as S. cyaneus by Morris (1967)), P. mariana (63), P. rubens (6), Pinus contorta (1), P. ponderosa (6), Pseudotsuga menziesii (7), and Tsuga heterophylla (2). We have only two records from Thuja plicata (2), a Cupressaceae. The record on Populus (1) is probably incorrect.

Based on 244 field-collected specimens, the earliest and latest capture dates are July 10 and September 25. The main flight period is from the first half of July to early October with a peak in September. Harrington (1882a) reported later dates up to October 18.


CANADA: AB, BC, MB, NB, NF, NS, NT, NU, QC, ON, SK, YT. USA: AK, CO, ID, MT, NH, NY, OR, UT, WA, WY. Sirex nitidus is a widespread species that occurs transcontinentally from Newfoundland to Alaska anywhere spruces grow in boreal, cold temperate, and mountain zones (Fig. C13.8). We have seen several intercepted specimens from New Zealand (FRNZ and PANZ).

Specimens studied and included for distribution map: 658 females and 203 males from BDUC, BYUC, CASS, CNC, CUCC, CUIC, DEBU, EDUM, FRLC, GLFC, LECQ, LEMQ, MNRQ, MTEC, NFRC, NFRN, OSAC, PFRC, UAIC, UAM, UASM, USFS–AK, and USNM.

Specimens of S. nitidus for molecular studies: 47 specimens. See Fig. E2.5d.

CANADA. British Colombia: 2002, SIRCA 056, 393; 2002, SIRCA 057, 605; 2001, SIRCA 058, 613; 1999, SIRCA 059, 612; 2002, SIRCA 060, 604; 2001, SIRCA 067, 604; 2004, SIRCA 090, 639. Nova Scotia: 2005, CBHR 292, 658; 2005, CBHR 293, 658. Ontario: 2006, CBHR 1096, 658; 2006, CBHR 1097, 658; 2006, CBHR 1098, 658; 2006, CBHR 1099, 611; 2006, CBHR 1101, 658; 2006, CBHR 1192, 658; 2006, CBHR 1193, 658; 2006, CBHR 1195, 658; 2006, CBHR 1196, 658; 2006, CBHR 1198, 658; 2007, SIRCA 006, 630; 2007, SIRCA 007, 595; 2007, SIRCA 008, 612; 2007, SIRCA 009, 604; 2007, SIRCA 010, 613; 2007, SIRCA 011, 613. USA. Minnesota: 2008, CBHR 1378, 658. Montana: 2004, CBHR 255, 658; 2006, CBHR 331, 658; 2006, CBHR 368, 658. New York: 2006, CBHR 599, 658; 2006, CBHR 608, 658; 2006, CBHR 615, 658; 2006, CBHR 636, 658; 2006, CBHR 640, 658; 2006, CBHR 644, 658; 2006, CBHR 740, 658. Oregon: 2005, CBHR 1057, 658; 2006, CBHR 1079, 658; 2006, CBHR 1083, 658; 2006, CBHR 1088, 658. Washington: 2005, CBHR 248, 658; 2005, CBHR 1056, 658; 2007, CBHR 1276, 658; 2007, CBHR 1277, 658; 2008, CBHR 1964, 658; 2008, CBHR 1967, 658; 2008, CBHR 1968, 658.

Specimens of S. sp. near nitidus for molecular studies: 6 specimens. See Fig. E2.5d.

USA. Colorado: 2005, CBHR 194, 658; 2005, CBHR 554, 658; 2005, CBHR 555, 658; 2005, CBHR 556, 658; 2005, CBHR 557, 658; 2005, CBHR 558, 658.