Fig. C12.1, Schiff et al. 2006: 32, 33 (female with black abdomen, habitus)
Fig. C12.2, Schiff et al. 2006: 46, 47 (female with mainly reddish brown abdomen, habitus)
Fig. C12.3, Schiff et al. 2006: 31 (male with dark abdomen, habitus)
Fig. C12.4, Schiff et al. 2006: 45 (male with pale abdomen, habitus)
Fig. C12.5 (live female with mainly reddish brown abdomen)
Fig. C12.6 (live male with dark abdomen)
Fig. C12.7 (live male with pale abdomen)
Fig. C12.10 (map)
Among females with a completely black body and legs and fore wing either darkly tinted or with dark bands near middle and apex [californicus and obesus], those of S. nigricornis are recognized by the long metatarsomere 2 (2.7–3.3 times as long as high, and dorsal length clearly longer than metatarsomeres 3 + 4), the crater-like pits on most of median half of the mesoscutum, and the very dense pits on the gena and most of the vertex (pits on gena 0.0–1.0 and on the vertex 0.0–0.5 pit diameters apart). Among females with mainly reddish brown abdomen [behrensii], those of S. nigricornis are recognized by the black edge of the cornus. Among males with black metafemur and reddish brown tibiae and tarsi of the fore and mid legs [longicauda and nitidus], those of S. nigricornis are recognized by the very dense pits on the gena and most of the vertex (pits on the gena 0.0–1.0 and on the vertex 0.0–0.5 pit diameters apart).
Color. Head thorax, antenna, palps, coxae, and femora (except apex in some specimens) black with dark blue metallic reflections. Legs in black form completely black, in pale form as follows: coxae and femora black, and tibiae and tarsi completely black to completely reddish brown (Figs. B2.28 & as in B2.27). Both wings lightly to darkly tinted (northern localities) (Fig. B2.31b) to darkly tinted (southern localities) (Fig. B2.31a). Abdomen in dark form completely black, in pale form as follows: basal segments 1 and 2 to as many as 1–4 black, remaining terga light reddish brown (except laterally in some specimens), remaining sterna completely reddish brown to black, basal section of sheath light reddish brown, apical section black at least in basal half (Fig. B2.15), lateral surface of tergum 9 broadly black, ventral surface of tergum 10 black at base and in anterior half (Fig. B2.15), and cornus dorsally at apex and laterally and widely ventrally black.
Head. Gena with pits 0.0–1.0 pit diameters apart (Fig. B2.33), vertex and postocellar area with pits 0.0–0.5 pit diameters apart (Fig. B2.35), and each pit diameter about 0.3–0.4 that of lateral ocellus.
Thorax. Mesoscutum with coarse, net-like pits over most of median area (Figs. B2.42, close–up C12.8). Metatarsomere 2 in lateral view 2.7–3.3 times as long as high, and its length 1.1–1.3 times length of tarsomeres 3 + 4 (Fig. B2.28); tarsal pad 0.3–0.4 times as long as ventral length of tarsomere. Fore wing vein 3A absent (Fig. B2.31b).
Abdomen. Median basin of tergum 9 with basal width 0.9–1.2 times as long as median length, maximum width 1.1–1.4 times as long as median length, and median length 0.7–0.9 times as long as cornus length. Cornus in dorsal view short, with edges clearly angular midway, its median length 0.8–0.9 times as long as maximum width of abdomen at junction of terga 9 and 10. Sheath. Length 0.57–0.69 times fore wing length, basal section 1.08–1.45 times as long as apical section. Ovipositor. Lancet with 30–35 annuli (basal annuli not clearly outlined); junction of basal and apical section of sheath aligned between 10th and 11th to 13th and 14th annuli, with 26–31 pits beginning with annulus 2; pit of annulus 2 clearly extended to annulus 1 (Fig. B2.37, base). Pits near middle annuli (Fig. B2.44) or area at base of apical section of sheath 0.35–0.45 times as long as an annulus (pits scarcely decreasing in size toward base), 0.55–0.65 times as high as lancet height in lateral view, and 1.3–1.5 times as long as high (Fig. B2.37, middle); annulus 10 length/ovipositor diameter (lance + lancet) not measured. Last 4-5 annuli before teeth annuli as well as first tooth annulus with ridge on ventral edge of pit. Edge of apical 5-6 annuli before teeth annuli extending as ridge to ventral edge of lancet.
Color. Head, thorax, antenna (flagellomeres 1 and 2 black to light reddish brown), palps, coxae, and femora (except apex on fore and middle legs in many specimens) black with dark blue metallic reflections. Tibiae, and tarsi of fore and middle legs light reddish brown (except for brown or black spot on tibia and tarsomeres 1 or 1 and 2 of middle leg in many specimens (Fig. B2.94)); Metatibia and metatarsus black (except metatarsomere 4 usually reddish brown); reddish brown spot at base of metatibia narrow, about as long as minimum width of tibia at base (Fig. C12.9). Fore wing light yellow tinted. Abdomen in pale form black on segments 1 and 2 to as many as 1–4, light reddish brown on terga 3–8 or 5–8, and black on sterna 3–9 or 6–9; in dark form abdomen black on segments 1–4 and on segments 7 and 8 (including sternum 9).
Thorax. Metatibia 4.3–4.6 times as long as maximum width (Fig. C12.9). Metatarsomere 1 in lateral view 3.2–3.5 times as long as maximum height.
Until this study, pale specimens of S. nigricornis were assigned to S. nigricornis whereas dark specimens were assigned to S. edwardsii. The two color forms have an unusually similar flight period (two periods, clearly separated), the same range, and adults may emerge from the same pine trunk. In addition, the proportions between the length of lancet annuli 2, 5 and 10 relative to the diameter of the ovipositor are similar for both color forms (based on 10 specimens for each color form). For both color forms combined (20 specimens), the annulus length/ovipositor diameter (lance + lancet) for annulus 2 1.6–2.1 (mean = 1.8), for annulus 5 1.1–1.6 (mean = 1.4), annulus 10 1.1–1.5 (mean = 1.3). Finally, the information from morphology and DNA barcoding confirms that the two populations are the same. Therefore, we regard these as two discrete color forms of a single species.
Two types were not examined: S. nigricornis Fabricius (pale form) and S. Edwardsii Brullé (dark form), but the original description and illustration for both species were adequate to allow us to match them with our concept of S. nigricornis, the oldest name.
Females of S. nigricornis with a pale abdomen could be confused with those of S. behrensii. In both sexes of S. nigricornis the banded pattern is absent in the fore wing, and fore wing vein 3A is absent (banded pattern clearly present in the fore wing, and fore wing vein 3A present in S. behrensii). Females of S. nigricornis lack the broad black longitudinal band along the side of the abdomen, the ventral surface of tergum 10 is black basally and at the side in anterior half, and the cornus is partly black (broad black longitudinal band along the side of the abdomen present, dorsal and ventral surfaces of tergum 10 without black spots, and cornus completely reddish brown in S. behrensii). Males of the two species are easily distinguished on antennal and hind leg color patterns.
The two color forms are not equally distributed. For instance in Ontario only 23% of trapped adults are the dark body form. The next significant sample is from Indian Head, Saskatchewan, and there 60% of 47 specimens belong to the dark body form. Father west at Lac La Biche in eastern Alberta, all eight specimens are black. So, a gradual increase westward occurs in the proportion of the dark body form.
Sirex nigricornis has a wide host range. Most rearing records are from various species of Pinus (94%) (Johnson 1928, Cameron 1965, Kirk 1974). Based on 229 reared and confirmed specimens all hosts are Pinaceae: Picea sp. (12), Picea abies (1), Pinus sp. (16), P. banksiana (58), P. clausa, P. echinata (68), P. elliottii, P. palustris, P. resinosa (21), P. rigida, P. strobus (42), P. sylvestris (8), P. taeda (1), and P. virginiana (2). Records from Populus sp. (Salicaceae) (4) and Quercus sp. (Fagaceae) (1) are most likely incorrect.
Based on 893 field-collected specimens, the earliest and latest capture dates are from late July to early October. There are two flight periods, a small one in the second half of July and a major one from mid August to late September with a peak in the second half of September.
CANADA: AB, BC (probably mislabeled), ON, QC, SK. USA: AL, AR, DC, FL, GA, LA, MD, MS, NC, NY, OH, PA, TN, TX, VA, WI, WV. If the possibly mislabeled record from British Columbia and one specimen (probably S. obesus) from Arizona reported by Cameron (1965) are ignored, S. nigricornis has an eastern range extending from Alberta to Quebec south to Louisiana and northern Florida (Webster 1895, Johnson 1928, Rohwer 1928, Ries 1951, Burks 1958, Burks 1967, Smith 1979, Chapin and Oliver 1986) (Fig. C12.10).
Specimens studied and included for range map: 1406 females and 1561 males from BYUC, CASS, CNC, CUCC, CUIC, DEBU, EDUM, FSCA, GLFC, MRNQ, NFRN, USFS–GA, and USNM.
Specimens for molecular studies: 53 specimens. See Fig. E2.5b.
CANADA. Ontario: 2007, SIRCA 002, 658; 2007, SIRCA 003, 557; 2007, SIRCA 004, 632; 2007, SIRCA 005, 619; 2007, SIRCA 014, 617; 2007, SIRCA 015, 629; 2007, SIRCA 016, 628; 2007, SIRCA 017, 624; 2006, CBHR 597, 658; 2006, CBHR 598, 658. USA. Georgia: 2006, CBHR 513, 658; 2006, CBHR 514, 658; 2006, CBHR 516, 658; 2006, CBHR 518, 658; 2006, CBHR 519, 658; 2006, CBHR 520, 658; 2006, CBHR 571, 658; 2006, CBHR 572, 658; 2006, CBHR 574, 658; 2006, CBHR 575, 658; 2006, CBHR 576, 658; 2006, CBHR 577, 658; 2006, CBHR 587, 658; 2006, CBHR 588, 658; 2006. Illinois: 2006, CBHR 170, 658. Indiana: 2005, CBHR 172, 658; 2005, CBHR 173, 658; 2005, CBHR 174, 658; 2005, CBHR 175, 658; 2005, CBHR 177, 658; 2005, CBHR 178, 658; 2005, CBHR 179, 658; 2005, CBHR 180, 658; 2005, CBHR 181, 658; 2005, CBHR 182, 658. Louisiana: 2005, CBHR 243, 658; 2005, CBHR 256, 658. Minnesota: 2008, CBHR 1384, 658; 2008, CBHR 1460, 658. Mississippi: 2001, CBHR 30, 658; 2001, CBHR 32, 658; 2001, CBHR 152, 658 ; 2001, CBHR 153, 658; 2001, CBHR 154, 658; 2001, CBHR 155, 658; 2001, CBHR 156, 658. New York: 2005, CBHR 205, 658; 2005, CBHR 206, 658. South Carolina: 2006, CBHR 512, 658; 2006, CBHR 894, 658. Unknown state: 2005, CBHR 120, 658; 2005, CBHR 121, 658.