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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

Urocerus gigas (Linnaeus)

Fig. C25.1 (female habitus)
Fig. C25.2 (male habitus)

Ichneumon gigas Linnaeus, 1758: 418. Holotype female (LSUK) images of type seen by HG. Thomson 1871: 328; Malaise and Benson, 1934: 12. See Smith (1978) for synonymy. Type locality: “Suecia”.
Sirex marisca Linnaeus, 1758: 560. Taeger et al. 2010.
Sirex hungaricus Christ, 1791: 414–415. Taeger et al. 2010.
Sirex psyllius Fabricius, 1793: 124–125. Taeger et al. 2010.
Urocerus Lefebvre Guérin, 1833: 68. Taeger et al. 2010.
Sirex Faustus Costa, 1894: 258. Taeger et al. 2010.
Urocerus gigas taiganus Benson, 1943: 39-41. Taeger et al. 2010.
Urocerus gigas var. luteigaster Berland, 1947: 77. Taeger et al. 2010.
Sirex gigas var. montana Ermolenko, 1957: 85.
Sirex gigas var. montanus Ermolenko, 1957: 6, not available. Nomen nudum. Taeger et al. 2010.

Diagnostic Combination

Among females with light reddish brown protarsomeres 2–5 [flavicornis and sah], those of U. gigas are recognized by the black pronotum and light reddish brown tergum 9. Males of U. gigas are recognized by the black head, the reddish brown terga 2–8 or 3–8 (rarely 3–7) and usually the less narrow metatarsomere 1 (4.5–6.3 times as long as high).



Color. Head black except for white spot behind eye extending from ventral edge of eye almost to postocellar furrow. Maxillary palp and mandible black. Scape, pedicel, and flagellum light reddish brown, and apex of last flagellomere not darkened. Thorax black. Coxae, basal 0.5–0.7 of pro- and mesofemur, and metafemur (except extreme apex) black; tibiae and tarsi light reddish brown. Fore and hind wings lightly yellow tinted. Abdomen black, but terga 1 (at least apical half), 2, 7, 8–10 (except side in most specimens) light reddish brown  (Fig. B4.14).

Head. Vertex densely pitted between the white genal spots. Surface below white genal spot narrowly pitted.

Thorax. Metatarsomere 2 in lateral view about 2.0 times as long as high, and its tarsal pad about 0.8 as long as ventral length of tarsomere.

Abdomen. Median basin of tergum 9 with base (outlined by two lateral black longitudinal furrows) about 1.7 times as wide as median length, with maximum width about 1.8 times as wide as median length, and with median length about 0.4 times as long as cornus length. Cornus in dorsal view constricted near base, and minimum width of constriction about 0.8 times maximum width subapically. Microsculpture of sublateral surface of tergum 8 (between spiracle and pitted sculpticells on central area) with meshes outlined and sculpticells flat; tergum 9 with dorsal surface lateral to median basin smooth and without meshes, and ventral surface with meshes and flat sculpticells. Sheath. Length 0.85–0.95 times length of fore wing; apical section 1.31–1.48 times as long as basal section. Ovipositor. Lancet with 24–32 annuli (annuli in basal 0.5 of lancet outlined but difficult to see); junction of basal and apical sections of sheath aligned between 6th and 7th annuli; apical part of lancet with 14–22 pits. Pits 0.2–0.3 times as long as an annulus, becoming gradually small, and disappearing at base of apical sheath section. Edge of last 8–11 annuli before teeth annuli extending as ridge to ventral margin of lancet.


Color. Head capsule black (below antennal sockets with one or more light reddish brown spots in a few specimens), except white genal spot behind eye extending from ventral edge of eye almost to postocellar furrow. Flagellum mostly white or light reddish brown, rarely darkened in apical 0.25. Thorax black. Legs black, but light reddish brown on pro- and mesotibia, white in basal 0.3 of metatibia, and reddish brown in basal 0.15 and on apex of metatarsomeres 1 (Fig. B4.69 hind leg). Wings clear. Abdomen black except light reddish brown on most of terga 2–8, or rarely on terga 3–8 or 3–7 (Fig. B4.67).

Head. Vertex densely pitted between the white genal spots. Surface ventral to genal white spot narrowly pitted.

Thorax. Metatibia 5.7-8.5 times as long as maximum width. Metatarsomere 1 in lateral view 4.5–6.3 times as long as maximum height (Fig. B4.69).

Taxonomic Notes

Females of U. gigas are distinguished from U. flavicornis females by abdominal color pattern. Males are very similar but are distinguished on abdominal color pattern and, in most specimens, on proportions of metatarsomere 1 and metatibia.

Biological Notes

The life cycle extends over three or more years. The biology was treated by Hanson (1939).

Hosts and Phenology

The host range of U. gigas is wide (Allard, 2008). All but one hosts are Pinaceae: Abies sp., A. alba, Cedrus sp., Larix sp., Picea sp., P. abies, P. sitchensis, Pinus sp., P. radiata, P. sylvestris, and Pseudotsuga menziesii. One specimen was recorded from Chamaecyparis (Cupressaceae).

Based on 7 field-collected specimens from the southern Hemisphere, the earliest and latest capture dates are October 31 to May 18, with peak flight in November and December.


ARGENTINA: first discovered in the provinces of Chubut, Rio Negro and Neuquén in 1993 (Klasmer, 2002, Allard, 2008). BRAZIL: Matto Grosso, Itumana River (an earlier record in 1880 (Ries, 1946: 218)). CHILE: Arauco (Contulmo, Pino), Temuco (Tronco), Bio–Bio, Italia, Malleco (Angel, Conguillio Nat. Park), Mulchen (Caledonia), and Nuble. First found after 1970 in North American conifer plantations (Allard, 2008). Urocerus gigas is an adventive species in temperate regions of South America. The species was commonly intercepted at United States ports and even in central Alberta. It was also often intercepted in New Zealand (FRNZ, NZAC and PANZ).

Specimens studied and included for the distribution map: 18 females and 11 males from AEI, AMNH, ANSP, CNC, NFRC, and USNM.

Specimens for molecular studies: 18 specimens. See Fig. E2.4c.

ARGENTINA: 2004, CBHR 51, 658. FINLAND: 2005, CBHR 840, 658; 2005, CBHR 841, 658; 2005, CBHR 842, 658; 2005, CBHR 843, 658; 2005, CBHR 844, 658; 2005, CBHR 845, 658; 2005, CBHR 846, 658; 2005, CBHR 847, 658; 2005, CBHR 848, 658; 2005, CBHR 849, 658; 2006, CBHR 851, 658; 2006, CBHR 853, 658; 2006, CBHR 856, 658; 2006, CBHR 857, 658; 2006, CBHR 860, 658; 2006, CBHR 861, 658; 2006, CBHR 865, 658; 2006, CBHR 866, 658; 2006, CBHR 870, 658; 2006, CBHR 871, 658; 2006, CBHR 872, 658. FRANCE: 1973, CBHR 158, 658. GREECE: year unknown, CBHR 581, 658.