Scolytus tsugae (Swaine, 1917)

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 52

Taxon classification Animalia Coleoptera Curculionidae

Scolytus tsugae (Swaine, 1917) Figs 52, 57

Eccoptogaster tsugae Swaine, 1917: 32.

Scolytus monticolae (Swaine, 1917): Keen 1929: 12.

Diagnosis.

Scolytus tsugae most strongly resembles Scolytus monticolae and the two species are easily and often confused. Both sexes are distinguished from those of Scolytus monticolae by the impressed elytral discal striae, giving the elytra a corrugated appearance, by the dull luster of ventrite 2 and the host genus Tsuga .

Description (male).

2.8-3.4 mm long (mean = 3.1 mm; n = 16); 2.1-2.5 times as long as wide. Body dark red-brown and antennae light brown. Pronotum typically darker than elytra.

Head. Epistoma weakly emarginate; epistomal process absent; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing flattened when viewed laterally, slightly transversely impressed just above epistoma; weakly longitudinally aciculate, moderately punctate; aciculations converging at epistoma; punctures small, coarse; moderately, uniformly covered by long, fine, erect, yellow, hair-like setae, these longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, irregularly ovoid, setose with partial septum, two arcuate sutures visible.

Pronotum wider than long; apical margin broadly rounded, median area between eyes lined with scales; sides distinctly arcuate, strongly constricted near apex, forming a weak transverse impression near apical margin; surface smooth, shining, punctures on disc fine, shallow, moderately abundant, larger and more abundant laterally and on apical constriction; apical and anterolateral margins bearing sparse, erect, dark yellow-brown, hair-like setae; base weakly bisinuate.

Elytra with sides sub-parallel on basal half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae weakly impressed, more than twice width of striae, interstrial punctures uniseriate, smaller than those of striae; striae weakly impressed, elytra with a corrugated appearance. Declivity bearing sparse, short, erect yellow setae. Metepimeron less than half-length of metanepisternum.

Venter. Apical margin of ventrite 1 weakly, continuously elevated above base of ventrite 2. Ventrite 2 nearly perpendicular to ventrite 1; surface glabrous, shagreened, dull, finely punctate; punctures small, fine, shallow; surface flattened; apical margin unarmed; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 greater than combined lengths of ventrites 3 and 4; setal patch and median depression absent.

Female.

2.3-3.5 mm long (mean = 3.0 mm; n = 16); 1.9-2.8 times as long as wide. Similar to male except epistoma feebly emarginate, epistomal process present, moderately developed, low, frons convex when viewed laterally, weakly strigate, setae sparser, shorter, less than width of eye; weakly transversely impressed between inner apices of eyes.

Specimens examined.

369.

Type material.

Lectotype Eccoptogaster tsugae Swaine: female, labeled "Entomological Branch, Ottawa, Canada No. 2251, female, J.M. Swaine Coll., Lectotype CNCNo. 9239" (CNCI). Lectotype designated Bright 1967: 674. Paralectotypes Eccoptogaster tsugae (CNCI), [Unspecified locality]: 2251 (CNCI-12, CUIC-2, EMEC-1), 2327 (CNCI-2).

Non-type material.

CANADA:BRITISH COLUMBIA: Adams Lake, 8.V.[19]22, R. Hopping, ex. Tsuga mertensiana (CASC-1). Bowman Creek, 10.VIII.1928, R. Hopping, ex. Tsuga heterophylla (CASC-2). Garibaldi, 7.VII.1988, R.J. Rabaglia (RJRC-1). Merritt, Midday Valley, 5.VI.1926, W. Mathers, 17134, lot 94, ex. Pinus ponderosa (CASC-1), 11.VI.1926, 17190, lot 23 (CNCI-1). North Vancouver, Lynn Canyon, 1.VI.[19]23, 17003, N.L. Cutler, ex. Abies amabalis (CASC-12, CNCI-2). Pender Harbour, 17189, lot 1, 11.V.[19]26, G.R. Hopping, ex. Tsuga heterophylla (CNCI-9); lot 2, 12.V.[19]26 (CASC-1, CNCI-8), lot 4, 29.V.[19]26 (CASC-1, CNCI-6), lot 5, 1926 (CNCI-1), 13.VI.1928 (CASC-4). Terrace, Mrs. W.W. Hippisley (CNCI-1). Trinity Valley, 16.VIII.1927, J.R. Howell (CASC-2), 1722, lot 46, 10.VII.1928, (CASC-1), lot 50, 24.VII.1928 (CASC-1), 17339, lot 12, 19.VI.[19]30, (CASC-2); 16.VI.1927, 17213, lot 27, E.A. Rendell (CASC-1). Vancouver, 11.VI.1935, A. Graham, ex. Tsuga mertensiana (CASC-2); 27.V.1939, W.G. Mathers, ex. Tsuga heterophylla (CASC-2), 31.V.1939 (CASC-5), 5.VI.1939 (CASC-3), 12.VI.1939 (CASC-3), 27.VI.1939 (CASC-5), 4.VII.1939 (CASC-1), 10.VII.1939 (CASC-2). UNITED STATES:CALIFORNIA:Alpine Co.: Ebbetts Pass, 8730 ft, 13.VIII.[19]63, D.E. Bright, ex. Tsuga mertensiana (CNCI-8, EMEC-9). El Dorado Co.: [Georgetown, 10 mi E.], Blodgett [Experimental] Forest, 2.VI.2003, K. Apigian (EMEC-1), 30.V.1986, K. Hobson (EMEC-1). Pollock Pines, 22.VI.[19]48, A. Bartel (EMEC-1). Lassen Co.: Grassy Lake, 27.IX.[19]14, lot 142, ex. Tsuga mertensiana (CASC-2). Nevada Co.: Tahoe National Forest, Sagehen Basin, Carpenter Ridge, 39.4149°N, 120.3109°W, 15.VII.2003, M. Caterino (SBMN-1). [Unspecified County]: Yosemite National Park, Hopk. U.S. 15727-A, 2.VII.1918, J.E. Patterson, ex. Tsuga mertensiana (OSAC-4). IDAHO:Bonner Co.: Priest River Experimental Forest, Hopk. U.S. 61810, 28.X.1978, M.M. Furniss, ex. Tsuga heterophylla (USNM-8). Priest Lake, Reader Bay, 6.VIII.1985, M.M. Furniss, J.B. Johnson, ex. Tsuga heterophylla (WFBM-54). Boundary Co.: Idaho Panhandle National Forest, Roman Nose, N48°40.911', W116°34.345', 4353 ft, 12.VIII.2010, S.M. Smith, A.R. Gillogly, ex. Tsuga heterophylla (MSUC-7). Kootenai Co.: Deception Creek Experimental Forest, Hopk. U.S. 58885-B, 10.VII.1968, M.M. Furniss, ex. Tsuga heterophylla (OSAC-1), 16.VII.1968 (OSAC-1), 24.VII.1968 (OSAC-4), 30.VII.1968 (OSAC-2), 8.VIII.1968 (OSAC-1). Magee, VII.[19]29, R.L. Furniss, ex. hemlock [= Tsuga sp.] (OSAC-4). MONTANA: [Unspecified County]: Glacier [National] Park, 8.VII.[19]49, D. Giuliani (CASC-1). OREGON: [Douglas Co.]: Diamond Lake, Hopk. U.S. 20959-A, VII.[19]31, R.L. Furniss, ex. Tsuga mertensiana (OSAC-18). Hood River Co.: Mount Hood National Forest, Hwy 35, Sherwood Forest campground, N45°19.278', W121°37.104', 4293 ft, 2.VIII.2010, S.M. Smith, ex. Tsuga heterophylla (MSUC-5). Klamath Co.: Crescent Lake, 6.VII.[19]60, ex. Tsuga mertensiana (CASC-4). Crater Lake [National Park], Hopk. U.S. 18.916-A, 22.V.[19]30, W.J. Buckhorn, ex. Tsuga mertensiana (OSAC-30), Hopk. U.S. 18,950-A, 16.VI.[19]31 (OSAC-44); Hopk. U.S. 18851-A, 14.VI.[19]31, J.A. Beal, ex. Tsuga mertensiana (OSAC-6, USNM-2); Hopk. U.S. 20537-A, 17.VI.[19]33, F.P. Keen, ex. Tsuga mertensiana (OSAC-19); 24.VIII.[19]62, D.E. Bright, ex. Tsuga mertensiana (CNCI-1); 12.VIII.1984, M.M. Furniss, ex. Tsuga mertensiana (WFBM-16); Hopk. U.S. 20807-A, R.L. Furniss, ex. Tsuga heterophylla (OSAC-2). Linn Co.: Santiam Pass 7.VII.[19]64 (EMEC-1). [Yamhill Co.]: McMinnville, 27.XI.1937, K.M. & D.M. Fender (OSAC-1). Washington:King Co.: Seattle, 27.V.[19]07 (OSAC-1), 10.IV.[19]12 (OSAC-2), 12.IV.[19]12 (OSAC-1). [Snohomish Co.]: [labeled King Co.] Mountlake Terrace, 20.VIII.[19]62, D.E. Bright, ex. Tsuga heterophylla (CNCI-4). UNSPECIFIED LOCALITY: Hopk. U.S. 13247-A, ex. Tsuga mertensiana (OSAC-2). Summit Viola Trail, 9.IX.1910, J.M. Miller, ex. Tsuga mertensiana (OSAC-1).

Distribution.

CANADA: Alberta, British Columbia. UNITED STATES: California, Idaho, Montana, Oregon, Washington (Fig. 36).

Hosts.

Tsuga heterophylla Sarg. (western hemlock) and Tsuga mertensiana (Bong.) Carrière (mountain hemlock).

Common name.

Hemlock engraver.

Biology.

Scolytus tsugae attacks fresh slash, the main bole and large branches of hemlock ( Edson 1967).

Scolytus tsugae is an uncommon and poorly studied species. The adult galleries are typically perpendicular to the grain of the wood and 4.0-10.0 cm in length (Fig. 25) ( Edson 1967; Furniss and Johnson 2002). Adult galleries score the cambium slightly more than the sapwood. However, Edson (1967) reported that specimens from a series in northern California produced an adult gallery that was oriented obliquely to the grain of the wood. Galleries consist of a central nuptial chamber and two egg galleries. Each egg gallery is extended perpendicular to the grain of the wood from the central nuptial chamber. Egg niches are irregularly spaced and faintly score the sapwood. Larval tunnels are extended parallel to the grain of the wood, etching the sapwood lightly at first and deeply near the pupation chamber. There is one generation per year and broods overwinter as larvae ( Furniss and Johnson 2002).

Collection notes.

The senior author collected this species from fresh logging slash limbs that were 6.0-10.0 cm in diameter in Idaho and Oregon.

Remarks.

The lectotype does not bear a locality label. Swaine’s (1917) description states the type series was collected at "Cherry Creek valley, Vernon District, British Columbia, Glacier, B.C., Jasper Park, Alta." from both Tsuga mertensiana and Pseudotsuga mucronata [= Pseudotsuga menziesii ]. In Bright’s (1967) lectotype designation he lists the locality of the lectotype as "Glacier, BC, XI-26-15, Tsuga mertensiana ".

For many years Scolytus monticolae was considered a synonym of Scolytus tsugae (see Scolytus monticolae remarks). In their paper describing the biology of Scolytus tsugae , McMullen and Atkins (1959) actually described the biology of Scolytus monticolae . In their investigation the species studied was from Pseudotsuga menziesii rather than Tsuga spp. and created vertical instead of transverse galleries.