Among females with metatarsomere 2, 2.0–3.0 times as long as high, and completely black body, legs and a clear fore wing [xerophilus], those of S. mexicanus are recognized by the few transverse ridges on the posterior half of the mesoscutum. Among males with brown femora, tibiae, and tarsi [californicus, obesus, and xerophilus], those of S. mexicanus are recognized by light reddish brown antenna (apical antennomeres may be a little darker) and coxae, and the clear fore wing.
Color. Body, legs, palps, and antenna black with dark blue metallic reflections. Fore wing clear.
Head. Gena with pits 0.0–0.5 pit diameters apart (Fig. C11.3), vertex and postocellar area with pits 0.0–0.5 pit diameters apart (Fig. B2.119), and each pit diameter about 0.25–0.3 that of lateral ocellus.
Thorax. Mesoscutum with few transverse ridges in posterior half of median area; pits large but not net-like (Fig. B2.46). Metatarsomere 2 in lateral view 3.0 times as long as high, and its length about 1.2 times as long as tarsomeres 3 + 4; tarsal pad 0.3 times as long as ventral length of tarsomere. Fore wing vein 3A present and clearly outlined (Fig. B2.48).
Abdomen. Median basin of tergum 9 with basal width as long as median length, maximum width 1.2 times as long as median length, and median length 0.8 times as long as cornus length. Cornus in dorsal view short, with edges straight, its median length 0.88 times as long as maximum width of abdomen at junction of terga 9 and 10. Sheath. Length 0.65 times fore wing length, and basal section 1.25 times as long as length of apical section. Ovipositor. Lancet with 32 annuli (basal annuli clearly outlined (Fig. B2.52)); junction of basal and apical section of sheath aligned between 15th and 16th annuli, with 28 pits beginning with annulus 2; pit outlined from annulus 2; pit of annulus 2 only extending to edge of annulus 1 (Fig. B2.52, base). Pits near middle annuli (Fig. B2.50) or area at base of apical section of sheath 0.5 times as long as an annulus (pits slightly decreasing in size toward base), 0.5 times as high as lancet height in lateral view, and 1.4 times as long as high (Fig. B2.52, middle); annulus 2 length/ovipositor diameter 1.35, for annulus 5 1.18, and for annulus 13 1.12 (1 specimen). Last 4 annuli before teeth annuli as well as first tooth annulus with ridge on ventral edge of pit. Edge of apical 5 annuli before teeth annuli extending as ridge to ventral edge of lancet.
Color. Body, head, palps, thorax, and abdominal segments 1 or 1 and 2 black with dark blue metallic reflections; remaining abdominal segments and antenna (a little darker apically) (Fig. B2.117) light reddish brown. Legs and coxae reddish brown (Fig. B2.121). Fore wing clear.
Thorax. Metatibia 3.4–3.8 times as long as maximum width (Fig. B2.121). Metatarsomere 1 in lateral view 2.7–3.2 times as long as maximum height.
Holotype female (FSCA), in perfect condition; labeled [White] “Mexico, D.F. 22 June 1980 Woodpile: Garage D. J. Pletsch” [White with red frame] “HOLOTYPE Sirex mexicanus Smith”. Type locality: Mexico, Distrito Federal.
Paratypes. 1 female and 4 males. MEXICO. Distrito Federal: 22.VI.1980, woodpile, garage D. J. Pletsch (3M, 1M allotype, FSCA). USA. Texas: Brownsville (Port of Entry), pallets, 20.VI.2005, M. A. Garcia (1 F, USNM).
The name mexicanus is the adjective derived from the country and capital name – most specimens were collected in the vicinity of Mexico City. This species may be the first of many to be discovered in Mexico.
The host of S. mexicanus is unknown; it may be on various species of Pinus because S. mexicanus is related to S. californicus, with a short apical sheath section, and annulus 2 with a trough. The type specimens were captured on June 20 and July 22.
Mexico: Distrito Federal; northern Mexico intercepted at Brownsville, TX. Sirex mexicanus is probably widespread as it is found from the vicinity of Mexico City to the port of entry at Brownsville, in southern Texas (Fig. C9.6).