Scolytus subscaber LeConte, 1876

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 50-52

Taxon classification Animalia Coleoptera Curculionidae

Scolytus subscaber LeConte, 1876 Figs 52, 55

Scolytus subscaber LeConte, 1876: 373.

Diagnosis.

The male most closely resembles those of Scolytus obelus and Scolytus praeceps . It is distinguished from that of Scolytus obelus by the sparse, obscure, fine and shallow punctures of ventrite 2, by the dull luster of ventrite 2 and by the geographic distribution. The male can be distinguished from that of Scolytus praeceps by the presence of a median denticle on the apical margin of ventrite 2. Females closely resemble those of Scolytus ventralis and are distinguished by the distinctly, moderately longitudinally aciculate and weakly punctate frons, and by the weakly produced apical margin of ventrite 1 that forms a weak carinate lip along the basal margin of ventrite 2.

Description (male).

2.0-4.3 mm long (mean = 3.5 mm; n = 20); 1.8-2.3 times as long as wide. Head, pronotum and abdominal venter dark red-brown, antennae light brown, legs dark red-brown to light brown, elytra red brown. Pronotum typically darker than elytra.

Head. Epistoma moderately, very broadly emarginate; epistomal process moderately developed and elevated; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing convex when viewed laterally, slightly transversely impressed just above epistoma; moderately, coarsely, longitudinally aciculate-punctate; aciculations converging at epistoma; punctures minute, fine; moderately and uniformly covered by long, fine, yellow, erect hair-like setae, these longer than width of midpoint of eye. Antennal scape short, elongate; club flattened, ovoid, setose with partial septum, three 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, yellow setae; base weakly bisinuate.

Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex moderately emarginated at suture. Margin of apical edge bearing small, fine punctures. Disc smooth, shining; interstriae not impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae; punctures bearing short, sparse, recumbent yellow setae slightly longer than size of a puncture (may be abraded); striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.

Venter. Apical margin of ventrite 1 strongly, acutely produced forming lip along base of ventrite 2, basal margin of ventrite 2 appearing impressed. Ventrite 2 nearly perpendicular to ventrite 1; surface glabrous, shagreened, dull, finely and obscurely punctate; punctures small, fine, shallow; surface weakly concave; apical margin armed with broad median denticle; 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.

3.1-5.0 mm long (mean = 3.85 mm; n = 20); 1.9-2.6 times as long as wide. Similar to male except epistoma feebly emarginate, epistomal process absent, frons more strongly convex when viewed laterally, weakly longitudinally aciculate, setae sparser, shorter, less than width of eye. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Second ventrite unarmed, surface weakly rugose, punctures larger, deeper.

Specimens examined.

111.

Type material.

Lectotype Scolytus subscaber LeConte: female, Vanc. [Vancouver, B.C.], Type 968" (MCZC). Lectotype designated Wood 1982: 443.

Non-type material.

UNITED STATES:CALIFORNIA:Alpine Co.: Stanislaus National Forest, Hermit Valley, Hopk. U.S. 19193-A, J.M. Miller, ex. Abies concolor (EMEC-1, OSAC-4). Humboldt-Toiyabe National Forest, Hwy 89, 6.6 mi E. NF 4188, N38°39.906', W119°38.540', 8011 ft, 24.VII.2010, S.M. Smith, ex. Abies magnifica (MSUC-3). El Dorado Co.: Echo Lake, Hopk. U.S. 18381-A, 27.V.[19]31, J.M. Miller, ex. Abies magnifica (CSUC-1, EMEC-17, OSAC-20, USNM-3). Lake Tahoe, Fallen Leaf Lake, 22.VII.1930, A.C. Browne (CASC-1). Uncle Tom’s, 0.1 road mile W., 28.VII-12.VIII.1978, J.A. Benedictis, ex. from pheromone trap baited with E-11 tetradecenyl acetate (EMEC-1). [Madera Co.]: Bass Lake, Hopk. U.S. 19376-A, 2.VII.[19]32, G.R. Struble, ex. Abies concolor (EMEC-2, OSAC-3). Sugar Pine [community], 12.VIII.1920, E. Schiffel (CASC-1). Placer Co.: Lake Tahoe, 1 mi N., 3.VIII.[19]67, G.T. Ferrell (EMEC-3). Plumas Co.: LaPort, Hopk. U.S. 17933-A, J.M. Miller, ex. Abies magnifica (EMEC-2, OSAC-2). [Unspecified County]: Stanislaus National Forest, Hopk. U.S. 19818, J.M. Miller, ex. Abies concolor (OSAC-1). IDAHO:Clearwater Co.: Pierce, 4 mi W.N.W., 18.VII.1973, H.L. Osborne, ex. flight trap (USNM-1). Latah Co.: 1992, M.M. Furniss, ex. Abies grandis (WFBM-1). Flat Creek, 11.II.1995, M.M. Furniss, ex. Abies grandis (WFBM-4). Harvard, 3.5 mi N.N.E., 6.VIII.1973, H.L. Osborne, ex. flight trap (USNM-1). Moscow, 20.VII.[19]73, LC-1 (USNM-1), 24.VII.[19]73, LC-1 (USNM-2). Potlatch, 4 mi N.E., 3.VIII.1973, H.L. Osbourne, ex. flight trap (USNM-1). OREGON: [Benton Co.]: [Corvallis], Kiger Island, IX.1922, W.J. Chamberlain (USNM-1). [Klamath Co.]: Crater Lake [National Park], 11.VI.[19]33, Hopk. U.S. 18966-A, W.J. Buckhorn, ex. Abies concolor (EMEC-4), 14.XII.[19]33 (EMEC-3, OSAC-20, WFBM-1). WASHINGTON: [Chelan Co.]: Lake Wenatchee [State Park], VII.[19]69 (EMEC-1). [King Co.]: Seattle, 9.VI.[19]12 (OSAC-2). [Thurston Co.]: Olympia, 25.IV.[18]94 (OSAC-2).

Distribution.

CANADA: British Columbia. UNITED STATES: California, Idaho, Montana, Oregon, Washington (Fig. 56).

Hosts.

Principal host: Abies grandis (Dougl. Ex D. Don) Lindl. (grand fir). Incidental hosts: Abies lasiocarpa (Hook.) Nutt. (subalpine fir), Abies magnifica A. Murr. (red fir).

Biology.

Furniss and Kegley (2011) provide a detailed and thorough account of the biology of Scolytus subscaber . Adults infest suppressed branches in the crowns of mature trees and are rarely found in slash ( Edson 1967; Furniss and Kegley 2011). Scolytus subscaber is also associated with a staining fungus, Spicaria anomala (Corda) Harz. that kills the host cambium ( Wright 1938).

Adult galleries are distinct from those of other Scolytus species. They are epsilon ( “ε”) shaped and deeply excavated in the sapwood (Fig. 25). The gallery consists of a central nuptial chamber and two egg galleries that are recurved around the nuptial chamber ( Edson 1967). The adult gallery is 2.0-5.0 cm in length and varies by branch size, with larger branches having larger galleries ( Furniss and Kegley 2011). Egg niches lightly score the sapwood. In Oregon 12-30 eggs are laid per gallery and in Idaho the upper limit appears to be 12 ( Furniss and Kegley 2011). Larval mines radiate from the egg gallery in all directions, often crossing each other. The larval mines are located in the phloem and cambium for about the first centimeter of their length. After the first centimeter, larval mines lightly score the sapwood. Pupation chambers are formed in the cambium or outer bark. There is one generation per year and the brood overwinters as larvae. In Idaho, flight occurs in July and adults leave the gallery once eggs have been laid ( Furniss and Kegley 2011).

Collection notes.

Old galleries of this species were observed by the senior author while hiking along the Tuolumne Grove Trail in Yosemite National Park on 23.VII.2010.

Remarks.

The lectotype bears a partial locality label. LeConte’s (1868) description states the lectotype was collected at Vancouver Island.