Scolytus unispinosus LeConte, 1876

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 52-56

Taxon classification Animalia Coleoptera Curculionidae

Scolytus unispinosus LeConte, 1876 Figs 52, 58

Scolytus unispinosus LeConte, 1876: 372.

Scolytus sobrinus Blackman, 1934: 23.

Diagnosis.

Scolytus unispinosus is very morphologically similar to Scolytus fiskei and Scolytus laricis . Males are distinguished from those of Scolytus laricis by the frons flattened when viewed laterally, never deeply impressed, less moderately abundant frontal setae (compared to dense) and by the host genus, Pseudotsuga . Males are distinguished from those of Scolytus fiskei by the following combination of characters: abdominal venter dull in luster, the base of the ventrite 2 spine extending from the apical margin to half the length of the segment and by the geographical distribution. The female is distinguished from that of Scolytus fiskei by the dull luster of ventrite 2 and is distinguished from that of Scolytus laricis by the finely aciculate-punctate frons; ventrite 1 joining base of ventrite 2 more obtusely, base of ventrite 2 not finely impressed, flush with ventrite 1; epistomal process weakly developed, almost indistinct.

Description (male).

2.2-3.2 mm long (mean = 2.7 mm; n = 15); 2.3-2.7 times as long as wide. Head, antennae, pronotum, and abdominal venter dark red-brown. Elytra and legs yellow-brown to light brown. Pronotum typically darker than elytra.

Head. Epistoma weakly emarginate; epistomal process present, weakly developed, low; median area above mandibles bearing dense patch of long, yellow, hair-like setae. Frons appearing flattened when viewed laterally from epistoma to vertex, slightly transversely impressed just above epistoma to inner apices of eyes; moderately, coarsely, longitudinally aciculate-punctate; aciculations converging at epistoma; punctures sparse, small, fine; sparsely, uniformly covered by long, fine, erect, yellow, hair-like setae, thesee 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, yellow, hair-like 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, twice width of striae, punctures uniseriate, smaller than those of striae; 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 less than half-length of metanepisternum.

Venter. Apical margin of ventrite 1 rounded, marked by weak carina. Ventrite 2 nearly perpendicular to ventrite 1; surface shagreened, dull, finely punctate; punctures small, fine, shallow, nearly obscure; covered with sparse setae that are less than length of segment 3; surface convex; apical margin armed with laterally compressed, median spine with base extending from apical margin to half length of segment, apex rounded; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge closer to apical margin of segment; length of ventrite 5 less than combined lengths of ventrites 3 and 4; setal patch and median depression absent.

Female.

2.2-3.0 mm long (mean = 2.7 mm; n = 15); 2.3-2.7 times as long as wide. Similar to male except epistoma feebly emarginate, epistomal process feebly developed, frons convex when viewed laterally, weakly longitudinally aciculate, setae sparser, shorter, less than width of eye; weakly transversely impressed between epistoma and inner apices of eyes. Second ventrite apical margin armed with acute median denticle, with base extending from apical margin to half-length of segment.

Specimens examined.

654.

Type material.

Lectotype Scolytus unispinosus LeConte: male, labeled "Or. [Oregon], Type 965" (MCZC). Lectotype designated Wood 1982: 432. Holotype Scolytus sobrinus Blackman: male, labeled "Burke Colr, Kent, WA, Pseudotsuga taxifolia [= Pseudotsuga menziesii ], Hopk. US 41900, Type No. 43838" (USNM). Synonymy: Wood 1966: 30. Paratypes Scolytus sobrinus Blackman UNITED STATES:OREGON: [Jackson Co.]: Little Applegate River, Hopk. U.S. 14238-B, J.E. Patterson (EMEC-6). Ashland, Hopk. U.S. 14264-T, F.P. Keen (EMEC-3). WASHINGTON: [King Co.]: Kent, Hopk. U.S. 4190-A, [H.E.] Burke, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-5).

Non-type material.

CANADA: BRITISH COLUMBIA: Cloverdale, 28.XII.[19]22, N.L. Cutler, ex. Tsuga heterophylla (CASC-32, CNCI-11). Duncan, Genoa Bay, 10.VII.1928, W.G. Mathers, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (CNCI-1). Indian Meadows, Midday Creek, 13.VII.1920, R. Hopping, ex. Pinus ponderosa (CNCI-1). Merritt, Midday Valley, 31.V.1926, W. Mathers (CNCI-1), 2.VII.1926 (CNCI-2); R. Hopping 3.VIII.1923 (CNCI-1), 15.VIII.19[23] (CNCI-1), 7.VII.1926 (CNCI-1). Nanaimo, [Pacific] Biological Station, 23.VI.1920 (CASC-1). Nelson Island, West Lake, 1701, 23.VI.1922, R. Hopping, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (CNCI-12). Oliver, 25 mi N.W., 15.VI.1958, H. & A. Howden (EMEC-3). Pender Harbour, 30.VI.1928, G. Hopping, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (CASC-2). Squamish, Diamond Head trail, 3200 ft, 9.VIII.1953, G.J. Spencer (CNCI-1). Shuswap, 24.IV.[19]13, T. Wilson, ex. Douglas fir [= Pseudotsuga menziesii ] (CNCI-1). Vancouver, 7.VI.1934, W. Mathers ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (CASC-1), 11.VI.1934 (CASC-2). Vanguard, 23.VI.[19]32, R. Hopping, ex. Pseudotsuga mucronata [= Pseudotsuga menziesii ] (CASC-2, CNCI-2). Vernon, 27.V.1932, R. Hopping (CASC-1). UNITED STATES:CALIFORNIA:Del Norte Co.: 3.VII.[19]24, E.B. Leach (EMEC-1). El Dorado Co.: [Georgetown, 10mi E.], Blodgett Experimental Forest, 4000 ft, 26.V.1986, Hobson, Atkinson, ex. Lindgren trap, ponderosa pine resin, H&L B.P. fractions, burned over area (EMEC-3); 27.V.1986, Hobson, Irving, ex. Lindgren trap, ponderosa pine resin, untreated Oleo, burned over area (EMEC-2); 30.V.1986, Hobson, Atkinson, ex. Lindgren trap, unbaited, logged area (EMEC-1); 30.V.1986, Hobson, Atkinson, ex. Lindgren trap, unbaited, burned over area (EMEC-2). Placerville, Hopk. U.S. 33961-A, 26.III.[19]54, M.M. Furniss, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-16). Pollack Pines, 22.VI.[19]48, R.C. Bynum (EMEC-6). Humboldt Co.: Blocksburg, 13.V.[19]34, B.P. Biven (CASC-2). Orleans, 15 mi N.W., 13.VI.[19]64, D.E. Bright, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-7). Orick, 11 mi S., 11.VI.[19]62, D.E. Bright, B.A. Barr, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (DEBC-4, EMEC-3). Lake Co.: Whispering Pines, 14.IV.1964, ex. Douglas fir [= Pseudotsuga menziesii ] (CASC-1). Los Angeles Co.: Coquillett (EMEC-2). Madera Co.: 1.VII.[19]38 (EMEC-1). Marin Co.: Inverness, 11.X.[19]61, D.E. Bright, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (DEBC-3, EMEC-2). [Mariposa Co.]: [Yosemite National Park], Yosemite Valley, Hopk. U.S. 2810, Hopkins (EMEC-4). Mendocino Co.: (CASC-7). 14.VII.[19]22, E.R. Leach (CASC-4). Bransomb, CDFA#870697, 11.VII.[20]01, M. Garvin, ex. Lindgren funnel trap with ISP (CSCA-1), 25.VII.[20]01 (CSCA-3). Flynn Creek between Comptche and Navarro, 17.VIII.1953, P.S. Bartholomew (CASC-1). Mill Creek, 20.III.[19]59, R.E. Stevens, ex. Douglas fir [= Pseudotsuga menziesii ] (EMEC-13). Noyo River, VI.1896 (CASC-14). Napa Co.: Angwin, 2 mi N.N.E., North side of Howell Mountain, 1300 ft, 24.V.1974, H.B. Leech, ex. emerged from log of Pseudotsuga menziesii (CASC-3, USNM-6), 7.VII.1974 (CASC-3), 20.VII.1974 (CASC-16), 21.VII.1974 (CASC-11), 22.VII.1974 (CASC-4), 23.VII.1974 (CASC-8), 25.VII.1974 (CASC-15), 26.VII.1974 (CASC-2, USNM-3), 27.VII.1974 (CASC-1), 28.VII.1974 (CASC-6, USNM-3), 1.VIII.1974 (CASC-3), 3.VIII.1974 (CASC-3). Callistoga, 26.V.[19]57 (CASC-4); 4.X.1947, T.O. Thatcher, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-3); 1.V.[19]63, D.E. Bright, ex. Pseudotsuga menziesii (EMEC-3). Nevada Co.: Grass Valley, 17.I.1961, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (CASC-2). Middleton [labeled as Lake Co.], Hopk. U.S. 37588-A, R.W. Bushing, ex. Pseudotsuga menziesii (EMEC-3), G.M. Thomas (EMEC-3). [Placer Co.]: Colfax, 1 mi E., Hopk. U.S. 34068-A, 31.I.[19]37, ex. Pseudotsuga menziesii (EMEC-4). Towle, 11.XI.1932 (EMEC-1). Plumas Co.: Walker Mine, 15.VII.[19]30 (EMEC-3). [San Francisco Co.]: San Francisco, Hopk. U.S. 8557, 11.V.[18]99, ex. on pine [= Pinus sp.] (EMEC-1), 15.V.[18]99 (EMEC-1). Santa Cruz Co.: 16.IV.[19]59, J.E. Henry (WFBM-16). Aptos, New Brighton Beach State Park, 13.IX.1986, D. Adams, ex. Pinus radiata (EMEC-54). Shasta Co.: Hat Creek, 17.VI.[19]62, D.E. Bright, B.A. Barr, ex. Abies concolor (EMEC-2). Siskiyou Co.: Grass Valley, 16.X.[19]60, R.W. Bushing, emerged XI.1960, ex. Pseudotsuga menziesii (EMEC-6). Sonoma Co.: (CNCI-1). Fort Ross, 2 mi E., 2.XI.1947, T.O. Thatcher, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-3). Mount Saint Helena, 3.VI.[19]31, E.C. Zimmermann, ex. digger pine [= Pinus sabiniana ] (EMEC-1); Hopk. U.S. 21,125-F, 3.IV.1934, R.L. Furniss, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-4). Sebastopol, Hopk. U.S. 32638-A, 20.I.1940, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (DEBC-4, EMEC-5). Stillwater Cove, 12.V.1951, H.R. Moffitt (EMEC-1). Trinity Co.: 14.V.[19]23, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (CASC-4). [Unspecified County]: (CUIC-7). Yosemite National Park, Hopk. U.S. 20953-B, 19.VI.1932, J.M. Miller, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-8). IDAHO:Bonner Co.: Sandpoint, 13.VI.931, N.M. Downie (FMNH-1), 9.VII.1977 (FMNH-1); 9.VII.1977 (FMNH-1). OREGON: [Benton Co.]: Corvallis, 17.IV.[19]16, W.J. Chamberlin, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-3); 8.VII.1946, K.R. Hobbs (EMEC-1). Coos Co.: Myrtle Point, 18.VI.[19]64, D.E. Bright, ex. Pseudotsuga menziesii (EMEC-10). Curry Co.: Agness, 6 mi S.W., 10.VII.1990, M.M. Furniss, J.B. Johnson, ex. Pseudotsuga menziesii (WFBM-6). Brookings, 12 mi E.N.E., 12.VIII.1990, M.M. Furniss, J.B. Johnson, ex. Pseudotsuga menziesii (WFBM-4). Illahe, 4 mi N., 9.VIII.[19]90, M.M. Furniss, J.B. Johnson, ex. Pseudotsuga menziesii (WFBM-2). Deschutes Co.: Deschutes National Forest, Black Butte Rd, Black Butte, N44°24.924', W121°38.323', 4212 ft, 31.VIII.2010, S.M. Smith, ex. Pseudotsuga menziesii (MSUC-44). Douglas Co.: Roseburg, W.J. Chamberlin, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (DEBC-2, EMEC-6, WFBM-2). [Grant Co.]: Dixie Pass, Malheur National Forest, 23.VI.1961, S.L. Wood, J.B. Karren, D.E. Bright, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (DEBC-5). Jackson Co.: Dead Indian Spring, 17.V.1962, J. Schuh (CNCI-1). Mistletoe, Hopk. U.S. 15753-A, P.D. Sergent, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-3), Hopk. U.S. 15753-B, 21.VIII.1918, P.D. Sargent (DEBC-5, EMEC-10). Pinehurst, 2 mi E., 18.VII.[19]64, D.E. Bright, ex. Pseudotsuga menziesii (CNCI-5, EMEC-6). Prospect, 10.VII.[19]64, D.E. Bright, ex. Pseudotsuga menziesii (CNCI-11, EMEC-14). [Klamath Co.]: Klamath Falls, 17.VI.[19]64, D.E. Bright, ex. Pseudotsuga menziesii (EMEC-2). [Lane Co.]: McCredie Springs, 19.VI.1961, D.E. Bright, ex. Tsuga heterophylla (CNCI-2). Vaughn, J. Pierce, ex. Douglas fir limbs [= Pseudotsuga menziesii ] (WFBM-4); 21.VI.1955, J.A. Rudinsky, J.R. Pierce, ex. Doug fir branches [= Pseudotsuga menziesii ] (WFBM-3). Linn Co.: Santiam Pass, 19.VI.1951, S.L. Wood, J.B. Karren, D.E. Bright, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (DEBC-1). [Malheur Co.]: Monument Peak, 25.IX.[19]53, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-3). [Marion Co.]: Clear Lake, 17.VIII.[19]51, R. Kangur, ex. Larch [= Larix sp.] ((EMEC-4, WFBM-2). [Multnomah Co.]: Portland, Hubbard, Schwarz (EMEC-2). [Umatilla Co.]: Tollgate, 30.VI.1950, E.S. McClurskey, ex. on aluminum roof (CNCI-1), 1.IX.1950 (CNCI-1). [Unspecified County]: Detroit, 25 mi E., 17.VII.1939, Schuh, Scott, ex. Tsuga mertensiana (FMNH-6). Middle Sister Mountain, 8000 ft, Hopk. U.S. 53349-G, 4.VIII.1968, M.M. Furniss, ex. on snowfield (WFBM-2). Portland, Wickham (CNCI-1). Tillamook burn, 18.VII.1941, R. Kangur (EMEC-1). Warm Springs Indian Reservation, 15.VIII.[19]51, R. Kangur, ex. Douglas fir [= Pseudotsuga menziesii ] (EMEC-4). WASHINGTON: [Clallam Co.]: Port Angeles, Hopk. U.S. 130, A.D. Hopkins, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-1). Port Williams [Marlyn Nelson County Park at Port Williams], Hopk. U.S. 168-F, A.D. Hopkins, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-1). Cowlitz Co.: Castle Rock, 10 mi E., 27.VI.[19]64, D.E. Bright, ex. Pseudotsuga menziesii (DEBC-18, EMEC-9). [Grays Harbor Co.]: Humptulips, 28.V.1914, E.C. VanDyke (CASC-3). [Kittitas Co.]: Easton (CASC-6, EMEC-2). Okanogan Co.: Disautel, 4.XI.1936, R.L. Furniss, ex. Pseudotsuga menziesii (OSAC-17, WFBM-7). [Pend Oreille Co.]: Metaline Falls, Hopk. U.S. 21340, 17.VII.1931, W.D. Bedard, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (WFBM-15). Skamania Co.: Mineral Springs, 27.VI.[19]64, D.E. Bright, ex. Pseudotsuga menziesii (EMEC-9). [Snohomish Co.]: [labeled King Co.] Mountlake Terrace, 20.VIII.[19]62, ex. Pseudotsuga menziesii (CNCI-3). Thurston Co.: Olympia, 7-30.V.1996, E. LaGasa, ex. Washington Department of Agriculture port trapping survey (WFBM-1). Yakima Co.: Naches, 14 mi W., Dry Creek Ridge, Snoqualamie National Forest, 3.VII.1965, R.B. Hutt (DEBC-2). [Unspecified County]: Mount Adams, Bird Creek, 6000-7000 ft, 2.VII.1925 (CASC-1). Mount Rainier National Park, 21.VIII.[19]62, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (CNCI-6).

Distribution.

CANADA: British Columbia. UNITED STATES: California, Idaho, Oregon, Washington (Fig. 51).

Hosts.

Pseudotsuga menziesii (Mirb.) Franco (Douglas fir) but also likely occurs in Pseudotsuga macrocarpa (Vasey) Mayr (bigcone Douglas fir) in Southern California. Incidental in Abies , Pinus and Tsuga .

Common name.

Douglas-fir engraver.

Biology.

Scolytus unispinosus is very common ( Chamberlin 1939; Smith pers. obs.) and attacks the boles and branches of weakened, injured, dying and recently killed Douglas fir. Populations of this species can build up in windfalls, slash and during drought when the species becomes capable of killing young trees ( Keen 1938; Chamberlin 1939; Wood et al. 2003). Outbreaks are sporadic and are of short duration ( Keen 1938; Wood et al. 2003).

The adult gallery of this species consists of a single egg gallery that extends with the grain of the wood (Fig. 25). The nuptial chamber includes a short extension at a 45° angle from the egg gallery and is located at one end on the egg gallery. The gallery deeply scores the sapwood and lightly scores the cambium ( Chamberlin 1958). The female deposits 40-100 eggs in egg niches on both sides of the egg gallery 0.5-1.0 mm apart ( Doane et al. 1936). Larvae extend their mines at a right angle to the egg gallery forming a fan shaped pattern ( Chamberlin 1939). There are two generations per year in California and the broods overwinter as either eggs or larvae ( Keen 1938; Wood et al. 2003). Adults emerge from late April through July (Keen 1958). In Oregon one generation per year has been observed at high elevations in and two at lower elevations ( Chamberlin 1939).

McMullen and Atkins (1962) reported some notes on the biology of Scolytus unispinosus in British Columbia and appear to have reported a combined account of Scolytus unispinosus and Scolytus fiskei (see Scolytus fiskei biology for more information). This paper was the main source of information regarding the biology of Scolytus unispinosus and served as the basis for describing the biology of the species in numerous publications (including Bright 1976; Furniss and Carolin 1977; Furniss and Johnson 2002; Wood et al. 2003). Chamberlin (1939, 1958) provides the most reliable source of information regarding the biology of the species.

Remarks.

There are 25 Scolytus sobrinus specimens bearing paratype labels found in the EMEC. These specimens are not designated as such by Blackman (1934) and have been labeled "not Paratype" by the authors. These specimens bear the following Hopkins numbers: 4205-A (EMEC-2), 4272-A (EMEC-4), 1968-D1 (EMEC-1), 1968-D3 (EMEC-1), 4273-B (EMEC-1), 4204 (EMEC-2), 4220-A (EMEC-3), 4226-D (EMEC-1), 4201-A (EMEC-2), 13232-C (EMEC-1), 17 (EMEC-1), 18 (EMEC-1), 19 (EMEC-2) and Sonoma, California (EMEC-3).

This species occurs along the western coastal states of the United States and British Columbia, Canada. The range of Scolytus unispinosus does not overlap with that of Scolytus fiskei except in south central British Columbia where species are sympatric in the Interior Plateau near Merritt.