Among females with completely black legs and darkly tinted fore wing [areolatus and dark legged form of californicus], those of S. obesus are recognized by the short metatarsomere 2 (1.5 times as long as high) in lateral view and the dense pits on the gena and on most of the vertex (pits 0.0–1.0 pit diameter apart). Among males with reddish brown femora, tibiae and tarsi [californicus, mexicanus and xerophilus], those of S. obesus are recognized by the black antenna (flagellomeres 1 or 1 and 2 may be reddish brown) and the yellow tinted fore wing.
Color. Body, legs, palps, and antenna black with dark blue metallic reflections. Fore wing darkly tinted.
Head. Gena, vertex and postocellar area with pits 0.0–0.5 pit diameter apart (Fig. C15.3), and each pit diameter about 0.3–0.4 times lateral ocellus diameter.
Thorax. Mesoscutum with some transverse ridges in median area; pits quite large but not coarse or net-like (Fig. B2.41). Metatarsomere 2 in lateral view 1.5 times as long as high, and its length as long as or shorter than length of metatarsomeres 3 + 4 (Fig. B2.39); tarsal pad 0.6 times as long as ventral length of tarsomere. Fore wing vein 3A absent.
Abdomen. Median basin of tergum 9 with basal width 1.1 times as long as median length, maximum width 1.4 times as long as median length, and median length 0.6 times as long as cornus length. Cornus in dorsal view short, with edges slightly angular midway, its median length 0.95 as long as maximum width of abdomen at junction of terga 9 and 10. Sheath. Length 0.7 times as long as fore wing length, basal section 1.15 times as long as length of apical section. Ovipositor. Lancet with 32 annuli (basal annuli clearly outlined); junction of basal and apical section of sheath aligned between 12th and 13th annuli, with 28 pits beginning with annulus 2; pit of annulus 2 only extending to edge of annulus 1 (as in Fig. B2.52, base). Pits near middle annuli (Fig. B2.43) or area at base of apical section of sheath 0.35 times as long as an annulus (pits not or hardly decreasing in size toward base), about 0.6–0.7 times as high as lancet height in lateral view, and about 1.3 times as long as high (as in Fig. B2.52, middle); annulus length/ovipositor diameter (lance + lancet) for annulus 2 1.76, for annulus 5 1.53, for annulus 10 1.4, and for annulus 13 1.37 (based on one specimen). Last four annuli before teeth annuli as well as first tooth annulus with ridge on ventral edge of pit. Edge of apical five annuli before teeth annuli extending as ridge to ventral edge of lancet.
Color. Head, thorax, antenna (flagellomere 1 or 1 and 2 may be reddish brown) (Fig. B2.112), palps, thorax, and abdominal segments 1 or 1 and 2 black with dark blue metallic reflections; remaining abdominal segments light reddish brown. Legs reddish brown, but black on coxae. Fore wing clearly yellow tinted (B2.114).
Thorax. Metatibia 3.7–4.1 times as long as maximum width. Metatarsomere 1 in lateral view 2.5–3.1 times as long as maximum height.
Adults of S. obesus is very similar to S. californicus, but both sexes are distinguished from those of S. californicus by the pit density dorsally on the head, females by a short metatarsomere 2, and males by color pattern of the flagellum.
Sirex obesus and dark winged females of S. californicus have been confused in the literature. Many females of S. californicus and all of those of S. obesus have very darkly tinted wings, so wing base tint is not diagnostic. Therefore, published information under S. obesus needs confirmation with voucher specimens (Middlekauff 1960, Cameron 1965).
One specimen of S. obesus was reared from Pinus ponderosa. Based on 15 field-collected specimens, the earliest and latest capture dates are July 30 to September 23. Thirteen males were caught at hill tops on August 12 (1), August 24 (1), September 20 (4) and September 23 (7).
MEXICO. USA: AZ, NM. Sirex obesus is known from forested regions of southwestern United States (Fig. C9.6) and has been intercepted from Mexico at Nogales, Arizona and Brownsville, Texas.
Specimens studied and included on range map: 11 females and 14 males from CNC, OSAC, UAIC, and USNM.
Specimens for molecular studies: 10 specimens. See Fig. E2.5f.
USA. Arizona: 2008, CNCS 1037, 599; 2008, CNCS 1038, 578; 2008, CNCS 1039, 606; 2008, CNCS 1040, 593; 2007, CNCS 1041, 599. New Mexico: 2004, CNCS 1091, 597; 2004, CNCS 1092, 597; 2004, CNCS 1093, 593; 2004, CNCS 1094, 584; 2004, CNCS 1095, 594.