Scolytus praeceps LeConte, 1876

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 42-45

Taxon classification Animalia Coleoptera Curculionidae

Scolytus praeceps LeConte, 1876 Figs 45, 46, 47

Scolytus praeceps LeConte, 1876: 373.

Scolytus abietis Blackman, 1934: 21. syn. n.

Scolytus opacus Blackman, 1934: 20. syn. n.

Diagnosis.

Scolytus praeceps is a morphologically variable species across its range. Both sexes most closely resemble Scolytus obelus and are differentiated by the absence of a median tubercle on the apical margin of ventrite 2 in both sexes. The female is differentiated from that of Scolytus dentatus by the presence of a weakly developed and almost indistinct epistomal process and smaller size.

Description (male).

1.8-3.2 mm long (mean = 2.5 mm; n = 20); 2.0-2.9 times as long as wide. Color dark red-brown to black, antennae yellow-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 convex when viewed laterally, slightly transversely impressed just above epistoma and along median line to upper level of eyes (may not be impressed in some specimens); moderately, coarsely, aciculate-punctate; aciculations converging at epistoma; punctures small, coarse; moderately, 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, 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, yellow, hair-like setae; base weakly bisinuate.

Elytra with sides sub-parallel on apical half, narrowing to subquadrate, smooth apex; apex weakly emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc glabrous, smooth, shining; interstriae not impressed, more than twice width of striae, punctures uniseriate, smaller than those of striae; striae not 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, finely punctate (obscurely punctate in some specimens); punctures small, fine, shallow; surface weakly concave; apical margin unarmed or armed with a longitudinal carina and blunt tubercle, appearing keel-shaped or a low median longitudinal carina; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 equal to combined lengths of ventrites 3 and 4; setal patch and median depression absent.

Female.

1.7-3.5 mm long (mean = 2.69 mm; n = 20); 2.0-3.0 times as long as wide. Similar to male except epistoma feebly emarginate, epistomal process absent, frons more strongly convex when viewed laterally, weakly aciculate, setae sparser, shorter, less than width of eye; entirely convex to weakly transversely impressed just above epistoma. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Apical margin of ventrite 2 unarmed or weakly longitudinally tumescent.

Specimens examined.

627.

Type material.

Lectotype Scolytus praeceps LeConte: female, labeled "Cali. [California, Calaveras, Crotch Coll], Type 967" (MCZC). Lectotype designated Wood 1982: 439. Holotype Scolytus abietis Blackman: male, labeled "8637iss [Sandpoint, Idaho], 6-20-[18]99, [A.D. Hopkins], Hopk. US 224, Type No. 43837" (USNM). Holotype Scolytus opacus Blackman: male, labeled "Ouray, Colo[rado], 7,500-8,000 ft., July 1-15, [18]97, HF Wickham, Type No. 43836" (USNM).

Non-type material.

CANADA: BRITISH COLUMBIA: [Big Creek Provincial Park], Lorna [Lake], 5.VIII.1926, H. Richmond, ex. Abies lasiocarpa (CASC-2). Duncan, Genoa Bay, 16.VIII.1928, W.G. Mathers, ex. Abies grandis (CNCI-10), 17.VIII.1928 (CASC-3). UNITED STATES:CALIFORNIA:Alpine Co.: Humboldt-Toiyabe National Forest, Hwy 88, N38°45.824', W119°51.498', 6262 ft, 24.VII.2010, S.M. Smith, ex. Abies concolor (MSUC-3). El Dorado Co.: Georgetown, 10 mi E., University of California Blodgett [Experimental] Forest, VI.[19]62, R.W. Stark, ex. Abies concolor (DEBC-3, EMEC-8); 30.V.1986, K. Hobson (EMEC-2), 1-2.VI.1986 (EMEC-2), 21-24.VI.1986 (EMEC-2), 1-7.VII.1986 (EMEC-9), 9-16.VII.1986 (EMEC-3); 2.VI.2003, K. Apigian (EMEC-2), 5.VI.2003 (EMEC-1). Ice House Reservoir, 25.V.2007, A.I. Cognato (MSUC-5). [Lake Tahoe], Fallen Leaf Lake, 6300 ft, 5.VII.1940, H.T. Reynolds (EMEC-2). Pacific House, 0.7 mi E., 2.VII.1989, F.G. Andrews, ex. flume (CSCA-1). Pacific House, 1 mi E., 1.V.1994, C.B. Barr, ex. seining El Dorado ditch (EMEC-1). South Lake Tahoe, 16.VI.1988, D. Adams, ex. reared from Abies concolor (CSCA-1). [Fresno Co.]: Huntington Lake, 23.VII.[19]19, F.C. Clark (CASC-52). Shaver [Lake], 14.IX.[19]08, Miller, ex. Abies concolor (CNCI-3). [Madera Co.]: North Fork, 22.VI.1935, R.P. Allen (EMEC-1). Marin Co.: Inverness, 8.VIII.[19]62, C.A. Toschi (EMEC-1). Mariposa Co.: Yosemite Valley, 7.VII.1921 (CASC-21). Mendocino Co.: Noyo River, VI.1896 (CASC-2). Modoc Co.: Alturas, Knox Mountain, 8.VII.1964, D.L. Dahlsten (EMEC-1). Warner Mountains, 4.VII.1919, G. Hopping, ex. Abies concolor (CASC-4, USNM-2). Monterey Co.: 30.VII.1964, D.E. Bright, ex. Abies bracteata (CASC-8). Carmel Valley, 15 mi S., 22.VI.1963, C.J. Wray, ex. Abies bracteata (CNCI-7, DEBC-1, EMEC-5). Williams Canyon, Los Padres National Forest, 24.IV.1992, D.E. Bright, G. Ferrell, ex. Abies bracteata limbs (CNCI-22). Nevada Co.: Donner Memorial State Park, 10.IX.[19]87, S. Seybold, ex. collected on Abies concolor (CNCI-2, EMEC-1), 11.IX.[19]87 (CNCI-1, EMEC-1), 29.X.1987 (CNCI-2, EMEC-2). Nevada City, 28.V.1939, R.P. Allen (CNCI-5). Riverside Co.: Mount San Jacinto State Park, 33.807°N, 116.654°W, 15.VII.2003, M. Caterino (SBMN-1). Santa Rosa Mountain, 15.IX.[19]56, D.E. Bright, D.N. King, ex. Abies concolor (EMEC-4). San Bernardino Co.: San Bernardino National Forest, E. of Arrowbear Lake, 34.2076°N, 117.0584°W, 29.V.2004, M. Caterino (SBMN-2); S. Fork Trail, 34.1297°N, 117.8426°W, 28.V.2004, M. Caterino (SBMN-1). San Bernardino Mountains, Dollar Lake trail, 10.VII.1956, R.W. Bushing (EMEC-2), 11.VII.1956 (DEBC-1, EMEC-10). Sierra Co.: Calpine, 2.3 mi N.W., 5200ft, 27.VIII.1961, H.B. Leech, ex. under bark of Abies sp. (CASC-9). Siskiyou Co.: McCloud, 14.VI.1961, S.L. Wood, J.B. Karren, D.E. Bright, ex. Abies concolor (DEBC-5). Mount Shasta, 28.VII.1980, A.J. Gilbert (CASC-1). Trinity Co.: Klamath National Forest, FR 41N16, 0.2 mi E. FR 93, N41°14.822', W122°53.562', 5081ft, 28.VII.2010, S.M. Smith, ex. Abies concolor (MSUC-2). Tuolumne Co.: Cow Creek, 5 mi N. Strawberry, 18.VII.1964, C.W. O’Brien, ex. Abies sp. (CASC-102, DEBC-11). Pinecrest, Hopk. U.S. 19192-A, 29.VII.1930, G.R. Struble, ex. Abies concolor (DEBC-3); IX.1966, emerged 28.III.1967, G.T. Ferrell, ex. Abies concolor (EMEC-4). Sierra Village, 10.VII.1966, B.A. Tolden (EMEC-1). [Unspecified County]: Shasta [-Trinity] National Forest, Hopk. U.S. 21078, 10.V.1934, K.A. Salmon (DEBC-4). COLORADO:Clear Creek Co.: Idaho Springs, 12 mi S., 12.VII.2007, D.E. Bright, B.A. Barr, ex. bole Abies lasiocarpa (CSUC-2, DEBC-4). Eagle Co.: Basalt Mountain, 20.VI.1996, D. Leatherman (CSUC-1). IDAHO: [Bonner Co.]: Sandpoint, 2.VII.1964, N.M. Downie (FMNH-1). Clearwater Co.: Angel Butte thinning, T37N R3E, sec 3, ex. Abies grandis #86 (USNM-10). Kootenai Co.: Coeur d’Alene, 28.IV.1922, H.J. Rust, ex. Abies grandis (MSUC-3); 15.V.1951, 2157 ft, W.F. Barr, ex. Abies grandis (EMEC-3). Latah Co.: Moscow Mountain, 46.8042, -116.830183, 2713ft, 10.VIII.2010, S.M. Smith, [A.R. Gillogly], M.M. Furniss, ex. Abies lasiocarpa , emerged II.2011, M.M. Furniss (MSUC-72). Lewis Co.: Nezperce, 3 mi N., 3.VII.[19]69, R.C. Biggum (EMEC-1). OREGON:Deschutes Co.: Deschutes National Forest, Black Butte Rd, Black Butte, N44°24.924', W121°38.323', 4212 ft, 31.VII.2010, S.M. Smith, ex. Abies grandis (MSUC-91). Paulina Lake, 2 mi W., 12.VI.1940, Schuh, Scott, ex. Abies concolor (EMEC-2). Douglas Co.: Diamond Lake, 9.VII.[19]64, D.E. Bright, ex. Abies sp. (EMEC-7). Jackson Co.: Copper, 2 mi N., 3.IX.1970, W.G. Harwood, ex. Abies lasiocarpa , emerged 21.X.1970 (MSUC-7). [Klamath Co.]: Keno, 16.VII.[19]29, J.A. Beal, ex. Abies concolor (CSUC-2). Linn/Lane Co.: Blue River, 11 mi N.E., H.J. Andrews Experimental Forest, 5.VIII.1988, log decomp study, site 2, SE1/4 S15 T15S RSE, trap 2WA (OSAC-1). [Umatilla Co.]: Tollgate, 6.VI.[19]49, C. Chastain, ex. Abies grandis (CSUC-3, EMEC-2, FMNH-1). UTAH:Utah Co.: Hobble Creek Canyon, 14.VI.[19]60, D.E. Bright, ex. Abies concolor (DEBC-2). [Unspecified County]: (CNCI-1). 1952, T.O. Thatcher (CSUC-10). WYOMING:Albany Co.: Snowy Mountains, [Medicine Bow National Forest], Spruce campground, 6.IX.2010, D.E. Bright, B.A. Barr coll., ex. Abies concolor branches (DEBC-2). [Carbon Co.]: Saratoga, Hopk. U.S. 31518-E, 1.IX.[19]38, ex. Abies lasiocarpa (CSUC-1).

Distribution.

CANADA: Alberta, British Columbia. UNITED STATES: California, Colorado, Idaho, Montana, Oregon, Utah, Washington, Wyoming (Fig. 48).

Hosts.

Abies concolor (Gord. & Glend.) Lindl. ex Hildebr. (white fir), Abies grandis (Douglas ex D. Don) Lindl. (grand fir), Abies lasiocarpa (Hook.) Nutt. (subalpine fir) and Abies bracteata (D. Don) Poit. (bristlecone fir).

Biology.

Scolytus praeceps prefers to colonize fresh slash but is also found in small limbs and tops of small standing trees ( Edson 1967; Bright and Stark 1973).

The adult gallery contains two egg galleries that branch from the central nuptial chamber. Typically, one egg gallery extends from the nuptial chamber perpendicular to the grain of wood and the second egg gallery extends at a 45° angle to the grain (Fig. 24). Occasionally both egg galleries are extended obliquely to the grain, at a 45° angle to the grain or perpendicular to the grain ( Edson 1967). Galleries are frequently initiated near branch crotches and disguised under rough patches of bark. The adult gallery equally scores the sapwood and cambium. The adult galleries range in size from 2.5-6.4 cm in length. Eggs are laid in niches on both sides of each egg gallery and larval mines radiate perpendicular to the egg gallery. The larval mines gradually diverge forming a fan shaped pattern and lightly etch the sapwood. Pupation occurs in the sapwood ( Edson 1967). There is one generation per year and broods overwinter as larvae ( Furniss and Johnson 2002).

Remarks.

There has been a great deal of historical uncertainty regarding the placement of Scolytus abietis and Scolytus opacus since they were described. The species are extremely morphologically similar and thus difficult to differentiate. This similarity led several authors to treat Scolytus abietis as either a synonym of Scolytus opacus ( Wood 1982) or as a subspecies ( Bright 1976). Equihua-Martínez and Furniss (2009) removed Scolytus abietis from synonymy with Scolytus opacus based on differences in host use, submentum shape, and striations on the underside of the head and characters of the second ventrite including setae, punctures and spine shape. The species Scolytus abietis , Scolytus opacus and Scolytus praeceps were not recovered as monophyletic in any of our analyses (Figs 2, 8, 9). We observed very low intraspecific COI and ArgK nucleotide differences among populations (COI: 0-0.0049; mean = 0.0032), (ArgK: 0-0.0044; mean = 0.0024) and no differences in 28S or CAD (Table 6). Considerable variation was also observed in the shape of the spine on the male second ventrite, especially within Scolytus praeceps . Scolytus abietis and Scolytus opacus are here placed in synonymy with Scolytus praeceps because they were recovered as polyphyletic (Figs 2, 8, 9), there are minute molecular difference among populations sampled from California, Oregon, Idaho and Wyoming (Table 6), the species have identical galleries ( Edson 1967, Wood 1982) and variability of the spine on male ventrite 2.

The lectotype of Scolytus praeceps bears a partial locality label. LeConte’s (1868) description states that the lectotype was collected at Calaveras, California by Mr. Crotch.