header image
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

Genus Tremex Jurine

Fig. C36.1 (live female)

Tremex Jurine, 1807: 80. Type species: Sirex fuscicornis Fabricius, designated by Latreille, 1810: 436.
Sirex (Xyloterus) Hartig, 1837: 385. Type species: Sirex fuscicornis Fabricius, designated by Rohwer, 1911: 92. Name preoccupied by Xyloterus Erichson, 1836.
Xyloecematium Heyden, 1868: 227. Replacement name for Xyloterus Hartig.

Diagnostic Combination

Both sexes of Tremex are easily distinguished from other genera with antennal sockets far apart [all Tremecinae genera except Xeris] by cell 2R1 about as long as or longer than cell 3R1, and fewer than 15 flagellomeres. Females also have a mainly smooth median basin and no cercus.


Head. Antennal sockets with distance between their inner edges 4.0–5.0 times distance between inner edge of eye and outer edge of socket (Fig. B1.3). Distance between inner edges of lateral ocelli 1.6–2.2 times as long as distance between outer edge of lateral ocellus and nearest edge of eye (Fig. B1.1). Maximum distance between outer edges of eyes clearly less than maximum width of head (thus, in frontal view, genal edges completely visible and not intersected by outer edge of eyes) (Fig. B1.1). Minimum distance between inner edges of eyes about as long as maximum height of eye (Fig. B1.1). Gena without ridge behind eye and without white spot (Fig. B3.1), with large pits, each with posterior edge raised as low tooth (Fig. C36.2). Head with setae sharp at apex. Antenna with 11–14 antennomeres, and middle flagellomeres in dorsal view 0.8–0.9 times as long as wide  (Fig. B1.24); middle flagellomeres with sensory pits over ventral and most of dorsal surface (part of outer lateral surface without sensilla) and ventral surface not sharply separated from dorsal surface by a fold, especially on inner side.

Thorax. Pronotum smooth or pitted over less than 0.5 of anterior vertical surface. Mesoscutum densely pitted over median 0.5–0.7 only. Metatibia in male in lateral view metatibia about 5.0 times as long as maximum width, and in cross section about 1.5 times as high as maximum ventral width. Metatarsomere 1 0.8–0.9 times as long as maximum length of metatibia, and about as wide as maximum width of metatibia. In female, metatarsomere 2 in lateral view 2.0–3.0 times as long as maximum height. Metatarsomere 5 as long as metatarsomeres 2 or, in male of some species, as long as combined tarsomeres 2 + 3. Fore wing with apex acutely and angularly rounded, without vein 2 r–m, with cell 3R1 0.7–1.1 times as long as length of cell 2R1, with vein 2r-rs joining stigma in apical 0.2–0.3, with stigma parallel before junction but abruptly attenuated after junction with vein 2r-rs (Fig. B1.26), without vein Cu1, with 1cu–a joining vein Cu close to or at vein M, with vein SC scarcely outlined in basal 0.15, with vein 2A extending along posterior edge of wing for 0.5 times length of cell 1A, and with vein 3A present, long and clearly extending along posterior margin of wing (Fig. B1.26). Hind wing without anal cell (Fig. C1.26); hamuli present apical to junction of veins R1 and C (Fig. B1.12).

Abdomen. Female. Cornus in dorsal view short and lateral edges markedly convergent, but not constricted (Fig. B1.30). Terga 7, 8 and 9 (except laterally and ventrally, but including median basin) not pitted. Tergum 9 with median basin clearly wider than long, round, and sharply outlined for about 0.75 of median basin length (Fig. B1.30). Cercus absent. Sheath. Basal and apical sheath sections clearly separated by membrane; basal section 1.1–1.2 times as long as apical section; apical section slightly convex for most of its length, and with teeth dorsomedially in apical 0.2; median margin of basal section of sheath at very base without transverse ridges, but with setigerous pits in basal 0.3, each clearly raised as a forward directed tooth. Ovipositor. Lancet with 10–40 visible annuli; annuli outlined or not outlined at base (then present only under apical section of sheath); last annulus and first tooth annulus without pits or pits large and not sharply outlined on most of ventral edge, the preceding annuli with pits (Fig. C36.3); edge of last 3 annuli before teeth annuli and first tooth annulus extending as ridge toward ventral margin but not reaching it; edge of annuli before teeth annuli not sinuate (Fig. C36.3); each annular pit midway between dorsal and ventral edges of lancet not otherwise impressed; its edge sharp but not developed as tooth.

Taxonomic Notes

The genera Tremex and Afrotremex are very similar. The similar width of fore wing cell 2R1 equal to as much as 1.5 times as long as cell 3R1, the lack of a large tooth-like projection at the base of the cornus in females, the uniform pitted surface of the mesoscutum, the dense pits on the frons, the sharp setae of the frons and vertex, and the moderately deep pit sculpticells on the abdominal terga differentiate Tremex from Afrotremex. The size of cell 2R1 relative to cell 3R1 is the only character state supporting Tremex as a natural lineage distinct from Afrotremex.

Diversity and Distribution

This genus is found over the Holarctic Region and is especially diverse in eastern Asia. There are 33 known species (Taeger and Blank 2011, Taeger et al. 2010). Thirty two of these species are restricted to the Old World (Taeger and Blank 2011, Taeger et al. 2010). The New World diversity is very small. Only one indigenous species, T. columba (Linnaeus), and one introduced species, T. fuscicornis (Fabricius) are recorded. Because we studied only six additional species of this diverse Asiatic genus, our generic concept may be incomplete and one should expect that some Asiatic species may not fit one or more character states in the above description.

Species List

The 2 species treated are: