Scolytus ventralis LeConte, 1868

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 57-61

Taxon classification Animalia Coleoptera Curculionidae

Scolytus ventralis LeConte, 1868 Figs 52, 59

Scolytus ventralis LeConte, 1868: 167.

Diagnosis.

Males are distinguished from those of other species by having the base of ventrite 2 elevated, the surface of ventrite 2 flat, the apical margin of ventrite 2 often bearing a median denticle, and by the glabrous ventrite 2. Females most closely resemble those of Scolytus robustus and Scolytus subscaber . Females are distinguished from those of both species by the indistinctly and weakly aciculate and strongly punctate frons and by the apical margin of ventrite 1 flush with basal margin of ventrite 2, appearing rounded.

Description (male).

3.0-4.0 mm long (mean = 3.65 mm; n = 20); 2.1-2.7 times as long as wide. Head, pronotum and abdominal venter dark red-brown, antennae light brown, elytra and legs yellow-brown to light brown. Pronotum typically darker than elytra.

Head. Epistoma weakly emarginate; epistomal process weakly 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 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, irregularly 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, 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 large, coarse punctures. Disc glabrous, smooth, shining; interstriae not impressed, more than twice width of striae, interstrial punctures uniseriate, smaller than those of striae; striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.

Venter. Apical margin of ventrite 1 weakly 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 armed with broad median denticle, occasionally absent; 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.

2.2-4.6 mm long (mean = 3.56 mm; n = 20); 2.1-2.7 times as long as wide. Similar to male except epistoma feebly emarginate, epistomal process absent, 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 unarmed.

Specimens examined.

324.

Type material.

Lectotype: male, labeled "[Washington Territory] Type 970" (MCZC). Lectotype designated Wood 1982: 441.

Non-type material.

CANADA: BRITISH COLUMBIA: Duncan, Genoa Bay, 30.VI.1928, W.G. Mathers, ex. Abies grandis (CNCI-4), 21.VI.1928 (CNCI-1), 23.VI.1928 (CASC-1), 24.VI.1928 (CASC-1), 16.VII.1928 (CASC-1), 13.VIII.1936 (CASC-1). Steelhead, 6.VII.1933, H.B. Leech, ex. Abies amabalis (CNCI-1), 27.VII.1933 (CASC-1), 24.VII.1933 (CNCI-1), 26.VII.1933 (CNCI-1). Trail, 22 km S.E., 24.V.1991, J.E. Macias, ex. Abies grandis (CNCI-1). Vancouver, 10.VI.1935, K. Graham, ex. Abies grandis (CASC-12). MEXICO:Baja California: San Pedro Mártir, Hopk. U.S. 32716-A, 5.VI.1944, F.P. Keen, ex. Abies concolor (EMEC-1). UNITED STATES:ARIZONA:Cochise Co.: Coronado National Forest, Chiricahua Mountains, 14.VII.2009, J. Hulcr, ex. Pseudotsuga menziesii (MSUC-3). CALIFORNIA: [Amador Co.]: Jackson, 31.III.[19]55, ex. Abies concolor (EMEC-1). Calaveras Co.: Big Trees [State Park], VII.1930, F.E. Blaisdell (CASC-1). El Dorado Co.: Bijou at south end of Lake Tahoe, H.B. Leech, ex. Douglas fir log [= Pseudotsuga menziesii ], emerged San Francisco, 18-20.V.1965, W.E. Kuhl (CASC-8). [Georgetown, 10 mi E.], Blodgett [Experimental] Forest, 30.V.1986, K. Hobson (EMEC-1), 11.VI.1986 (EMEC-1), 21-24.VI.1986 (EMEC-6), 25-27.VI.1986 (EMEC-1), 1-7.VII.1986 (EMEC-2), 9-16.VII.1986 (EMEC-4); 30.V.1986, Hobson, Atkinson, ex. Lindgren trap, unbaited over burned area (EMEC-3), ex. Lindgren trap, turpentine bait, logged area (EMEC-1); 27.V.1986, Hobson, Irving, ex. Lindgren trap, ponderosa pine resin H&L B.P. fractions, logged area (EMEC-1), ex. Lindgren trap, ponderosa pine resin, untreated oleo, burned over area (EMEC-1). Ice House Reservoir, 23.VI.[19]90, J.B. Johnson (EMEC-1). Pacific, 8.VII.[19]62, R.L. McDonald (CASC-1). Fresno Co.: Huntington Lake, 16.VII.[19]19, F.E. Blaisdell (CASC-5). Lassen Co.: Lassen National Forest, 20-25.VII.1994, S1/2 S35 T34N R7E, A.I. Cognato (MSUC-20, SBMN-4); Black Mountain Experimental Forest, VII.1995, A.I. Cognato (MSUC-1). Near Loon Lake campground, 6300 ft, 28. VII– 12.VIII.1978, J.A. De Benedictis (EMEC-1). Norval Flats, 5500 ft, 18.VII.[19]20, J.O. Martin, ex. Abies concolor (CASC-47). Uncle Tom’s, 0.1 road mile W., 28.VII-12.VIII.1978, J.A. De Benedictis (EMEC-1). Marin Co.: VI-VIII.[19]56, D. Giuliani (CASC-1). Mariposa Co.: Miami Ranger Station, 2mi S., 19.VII.1946, H.P. Chandler (DEBC-3). Miami Lodge, 17.VII.1946, G.R. Struble, ex. Abies concolor (CSUC-1). Mendocino Co.: Noyo River, VI.1896 (CASC-22). Modoc Co.: Modoc National Forest, Hwy 299, 5.3 mi W. Cedarville at creek near exit from ski area, 41°32.9' N 120°14' W, 9.IX.1995, J. Schweikert, ex. swept creek side plants (CASC-1). Davis Creek, 4 mi N.E., Sugar Hill, 6300 ft, 9.VI.1970, W. Middlekauff (EMEC-1). Nevada Co.: Sagehen Creek Field Station, 39.4298°N, 120.2429°W, 12-18.VIII.2003, M. Caterino, ex. FIT (SBNM-1). Near Sagehen campground, 39.4344°N, 120.2808°W, 15.VIII.2003, M. Caterino (SBNM-1). Sagehen Creek, 20.VII.1966, W.J. Turner (EMEC-1). [Placer Co.]: Cisco (USNM-1). Plumas Co.: Bartle, 9 mi N., 12-15.VI.1974, L. Green (EMEC-1). Chester, 8mi N.W., Warner Creek, 5000 ft, 21.VI.1989, E.E. Lundquist (CNCI-2). Janesville, 15-21.VIII.[19]50, M. Wasbauer, ex. Abies concolor (EMEC-1). Riverside Co.: Mount San Jacinto State Park, 33.800°N, 116.673°W, 15.VII.2003, M. Caterino (SBMN-1). Santa Rosa Mountains, 10.IV.[19]63, D.E. Bright, ex. Abies concolor (EMEC-1). [San Bernardino Co.]: San Bernardino Mountains, Dollar Lake trail, 10.VII.1956, H.W. Michalk (CSCA-1). Siskiyou Co.: Happy Camp, 18 mi N., 31.VII.[19]63, C.J. Wray, ex. Picea breweriana (DEBC-2, EMEC-1). Klamath National Forest, goosenest adaptive management area, 41.5°N, 121.9°W, 26.VII.2000, ex. pitfall 3-840 (SBNM-1). McCloud, 22.VI.1914 (CASC-23), 14.VI.1962, D.E. Bright, B.A. Barr, C. Hector (CASC-1). Tehama Co.: Mineral, 11.VIII.[19]35 (CASC-1). Trinity Co.: Carville, 30.VI.1913, ex. dug out of Abies concolor (CASC-1), 2400-2500 ft, 23.V.1934 (CASC-1). Nash Mine, 12.VI.1913 (CASC-1). Tulare Co.: Giant Forest, 6500 ft, VII.1908, Hopping (CASC-3). Kaweah, 100 ft, Hopping (CASC-1). Sequoia National Park, Redwood Canyon, 20.IX.1980, S.F. Muzzio (CASC-2). [Unspecified county]: COLORADO:Costilla Co.: Pass Creek, 17.VI.1976, D. Leatherman, ex. white fir [= Abies concolor ] (CSUC-4). Huerfano Co.: near Red Wing, 16.VI.1975, D. Leatherman, ex. white fir [= Abies concolor ] (CSUC-1). Las Animas Co.: Monument Lake, 6.VII.1994, S. Kelley, ex. white fir [= Abies concolor ] (DEBC-2). Pueblo Co.: SR 165, 5 mi S.E. San Isabel Millset trailhead, D. Leatherman, ex. burned white fir [= Abies concolor ] (CSUC-6). IDAHO:Benewah Co.: Plummer, 4 mi S., 14.VIII.1956, W.F. Barr, E.C. Clark, ex. Abies grandis (FMNH-1). Boundary Co.: Idaho Panhandle National Forest, Hwy 95, Robinson Lake campground, N48°58.200', W116°13.067', 2696 ft, 13.VIII.2010, S.M. Smith, A.R. Gillogly, ex. Abies grandis (MSUC-6). Kootenai Co.: Coeur d’Alene, 5.IX.1919, J.C. Evenden, ex. Abies grandis (MSUC-3). MONTANA: [Unspecified county]: Glacier [National] Park, 15.VII.[19]31 (CUIC-1). NEW MEXICO:Bernalillo Co.: Cibola National Forest, Sandia Peak, NM536, N35°11.655', W106°24.075', 8317 ft, 10.V.2010, S.M. Smith, A.I. Cognato, ex. Abies concolor (MSUC-1). [Otero Co.]: Cloudcroft, 900 ft, W. Knaus (CNCI-1). Santa Fe Co.: Little Tesuque Canyon, 14.VI.[19]35 (CASC-1). Socorro Co.: VII.[?], Wickham (CASC-1). OREGON:Benton Co.: Corvallis, VIII.1919, W.J. Chamberlin, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (EMEC-1), Kiger Island, VII.[19]22, W.J. Chamberlin (EMEC-2). Mary’s Peak, 14 mi W. Corvallis, XII.1958 (EMEC-2). [Deschutes Co.]: Bend, Hopk. U.S. 33,531-B, 8.VII.[19]58, W.J. Buckhorn, P.W. Orr, ex. Abies grandis (OSAC-8). [Klamath Co.]: Klamath Falls, Geary Ranch, 4.X.1962, J. Schuh, ex. Abies concolor (CNCI-2, FMNH-4, MSUC-7). [Linn Co.]: McMinnville, 7.VIII.1951, R. Kangur (WFBM-2). [Wallowa Co.]: Wallowa Lake, 19.VII.[19]51, Quintus, ex. Abies concolor (WFBM-1). UTAH:Juab Co.: Mount Nebo, 20.VII.1958, D.E. Bright, ex. Abies concolor (CNCI-2). Utah Co.: Payson Canyon, 20.V.1961, S.L. Wood, ex. Abies concolor (USNM-18). WASHINGTON: [Jefferson Co.]: Quilcene, Hopk. U.S. 65564, 30.IX.1946 (OSAC-6). [Pend Oreille Co.]: Metaline Falls, Hopk. U.S. 21405, 17.VII.[19]31, W.D. Bedard, ex. flying (USNM-4). [Stevens Co.]: Northport, 1.IX.1930, R. Hopping (CASC-3). [Walla Walla Co.]: Walla Walla, VIII.1933, M.C. Lume (USNM-11). [Yakima Co.]: [Mount Baker], Snoqualmie National Forest, Dry Creek Ridge, 14 mi W. of Naches, 3.VII.1965, R.B. Hutt (DEBC-1).

Distribution.

CANADA: British Columbia. MEXICO: Baja California. UNITED STATES: Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, Wyoming (Fig. 40).

Hosts.

Principle hosts: Abies concolor (Gord. & Glend.) Lindl. ex Hildebr. (white fir), Abies grandis (Douglas ex D. Don) Lindl. (grand fir), and Abies magnifica A. Murray (red fir). Incidental hosts: Abies lasiocarpa (Hook.) Nutt. (subalpine fir).

Common name.

Fir engraver.

Biology.

Scolytus ventralis can cause significant fir mortality and is the most destructive conifer-feeding Scolytus species in the Nearctic ( Keen 1938; Bright and Stark 1973). During a period from 1924-1936, Scolytus ventralis killed 15% and damaged an additional 25% of the merchantable fir in California. It has also been reported to be quite destructive in Oregon ( Keen 1938). Scolytus ventralis is associated with a symbiotic stain fungus, Trichasporium symbioticum Wright, which the adult beetle introduces when it excavates the adult gallery. The fungus spreads in all directions around the gallery system ( Bright and Stark 1973). Due to the potential of Scolytus ventralis to kill fir trees, this species is the most well studied native Scolytus in North America. Attacks usually occur on the boles of weakened and stressed standing trees from a few feet above the base to the top of the tree, but can also occur in large slash and fresh and fallen trees ( Chamberlin 1958; Edson 1967; Furniss and Johnson 2002). Attacks at the top of the tree are more common on overmature standing trees during drought and healthy, vigorous trees are not preferred ( Chamberlin 1958; Raffa and Berryman 1987). Trees can also become successively attacked over a period of years and slowly die. Healthy trees may survive the attacks but can develop rots and defects that reduce timber value ( Struble 1937). Unlike most tree-killing or primary bark beetles, Scolytus ventralis does not have pheromone to aggregate conspecifics to host trees. The beetles locate suitable hosts via primary attraction to host volatiles ( Macías-Sámano et al. 1998a, b).

Adult galleries are perpendicular to the grain of the wood (Fig. 25), deeply score the sapwood, lightly score the cambium and consist of two egg galleries with a central nuptial chamber ( Edson 1967). The nuptial chamber is typically short and at a right angle to the egg galleries but may also extend at an oblique angle. When this occurs, one of the egg galleries is briefly extended at an oblique angle against the grain before becoming perpendicular to the grain ( Edson 1967). Eggs are deposited singly in triangular niches spaced 1.0-1.5 mm apart on each side of the egg gallery with 80-300 niches per gallery. Galleries range in size from 8.0-30.0 cm in length ( Chamberlin 1958; Edson 1967; Bright and Stark 1973; Furniss and Johnson 2002). Larval mines are perpendicular to the egg gallery and parallel to the grain of the wood. Larval mines are also parallel to each other both above and below the egg gallery, giving the gallery a diamond shaped appearance ( Keen 1938; Edson 1967). Larval mines lightly score the sapwood and deeply score the cambium. Larvae construct pupation chambers in the phloem or outer bark ( Edson 1967). Broods overwinter as larvae or adults ( Bright and Stark 1973). The number of generations per year varies both geographically and with elevation. Development time can range from as little as 41 days at low latitudes and elevations to as many as 380 days at high latitudes and elevations ( Bright and Stark 1973). There is typically one generation per year ( Bright and Stark 1973). In Idaho pupation occurs from June to July and peak flight occurs in July ( Furniss and Johnson 2002).

Remarks.

The lectotype does not bear a locality label. LeConte’s (1868) description states that George Gibbs collected the lectotype in the Washington Territory.