Scolytus oregoni Blackman, 1934

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 39-41

Taxon classification Animalia Coleoptera Curculionidae

Scolytus oregoni Blackman, 1934 Figs 29, 42

Scolytus oregoni Blackman, 1934: 18.

Diagnosis.

Scolytus oregoni is a rather distinctive species and both sexes are readily distinguished by having the apical margin of ventrite 1 thickened and on the surface of ventrite 2 and by the unarmed ventrite 2.

Description (male).

2.6-3.6 mm long (mean = 3.3 mm; n = 20); 2.0-2.4 times as long as wide. Color dark red-brown, antennae brown. Pronotum typically darker than elytra.

Head. Epistoma weakly emarginate; epistomal process weakly developed; 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; moderately, coarsely, longitudinally aciculate-punctate; aciculations converging at epistoma; punctures sparse, 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, two strongly 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 weakly impressed. Declivity bearing sparse, short, erect, yellow setae. Metepimeron less than half-length of metanepisternum.

Venter. Apical margin of ventrite 1 not elevated above base of ventrite 2. Basal margin of ventrite 2 strongly thickened, lip-like; ventrite 2 nearly perpendicular to ventrite 1; surface shagreened, dull, finely punctate; punctures small, fine, shallow; surface weakly concave, weakly to strongly medially impressed just above base; apical margin unarmed; setae small, less than 1 diameter of a puncture; 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.

2.8-4.0 mm long (mean = 3.23 mm; n = 20); 1.6-2.7 times as long as wide. Similar to male except epistoma entire, epistomal process absent, frons convex when viewed laterally, weakly longitudinally aciculate, setae sparser, shorter, less than width of eye; weakly transversely impressed between inner apices of eyes. Second ventrite unarmed, basal margin weakly thickened.

Specimens examined.

96.

Type material.

Holotype, male, labeled "Ashland Ore., May 20/19, Glendinning, WE Colr, Pseudotsuga taxifolia , Hopk. US. 13399a, Type No. 43834 USNM" (USNM). Paratypes: UNITED STATES:Oregon: [Jackson Co.]: Ashland, Hopk. U.S. 14246-C, 10.III.[19]16, P.D. Sergent, ex. Pseudotsuga taxifolia (CNCI-2); II.[19]19, W.E Glendinning, Hopk. U.S. 1399-A (USNM-14).

Non-type material.

UNITED STATES:CALIFORNIA: [Del Norte Co.]: [Six Rivers National Forest], Gasquet R.S. [= Ranger Station], Hopk. U.S. 31722-H, 10.VII. R.L. Furniss, ex. Pseudotsuga taxifolia (OSAC-23). Lake Co.: Middletown, 11.XI.1959, G.M. Thomas, ex. Pseudotsuga menziesii (OSAC-1). Los Angeles Co.: Angeles National Forest, Sawmill Mountain, 34.6926°N, 118.5499°W, V.28-VI.14.2007, Caterino, Chatzimanolis, ex. Lindgren trap (SBMN-4). Marin Co.: Alpine Lake, V.[19]57 (CASC-4). Mount Tamalpais 14.IX.[19]57, E.L. Smith, ex. Pseudotsuga menziesii (OSAC-1). Woodacre Creek, 9.VII.1951, P.S. Bartholomew (CASC-1). Napa Co.: Angwin, 2 mi N.N.E., N. side of Howell Mountain, 1300 ft, 16.VII.1974, H.B. Leech, ex. emerged from log of Pseudotsuga menziesii (CASC-1), 21.VII.1974 (CASC-4, USNM-5), 22.VII.1974 (CASC-1), 25.VII.1974 (CASC-4, USNM-1), 7.VIII.1983 (CASC-1), 12.IX.1983 (CASC-2). Callistoga, 5.X.1947, S.L. Wood, ex. Pseudotsuga taxifolia (USNM-2). Mount Saint Helena, Hopk. U.S. 15401-A, F.B. Herbert, ex. Pseudotsuga taxifolia (OSAC-1). Riverside Co.: Santa Barbara National Forest, Black Mountain Rd, 33.8395°N, 116.7306°W, 1.VII.2005, M. Caterino (SBMN-1). [Valyermo Co.]: Fenner Canyon, Hopk. U.S. 33853-A, 15.VIII.[19]51, A.D. Moore, ex. Pseudotsuga macrocarpa (EMEC-3, OSAC-8, USNM-4). OREGON:Benton Co.: Marys Peak, Corvallis Watershed, 9.VIII.1963, ex. rotary traps (EMEC-1). Jackson Co.: Ashland, Hopk. U.S. 13363-B, 26.VI.1918, W.E.G, ex. Pseudotsuga taxifolia , (OSAC-14). Mistletoe, Hopk. U.S. 15753-A, P.D. Sergent, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (OSAC-3). Rogue River National Forest, Rogue River Gorge viewpoint, N42°54.540', W122°26.733', 3489 ft, 21.VIII.2010, S.M. Smith, ex. Pseudotsuga menziesii (MSUC-3). Linn/Lane Co.: Blue River, 11 mi N.E., H.J. Andrews experimental forest, 5.VIII.1986, Log Decomp Study, Site 2, SE1/4 S15 T15S RSE, Trap 2WA (OSAC-1). [Tillamook Co.]: Woods, 18.XI.[19]38 (OSAC-1). Wasco Co.: The Dalles, ODA Port/Mill survey, Trap #65-01a, 14.VIII.1997, ex. Lindgren funnel with α-pinene & ethanol lure (MSUC-1).

Distribution.

UNITED STATES: California, Oregon, Washington (Fig. 30).

Hosts.

Pseudotsuga menziesii (Mirb.) Franco (= Pseudotsuga taxifolia Britton) (Douglas fir) and Pseudotsuga macrocarpa (Vasey) Mayr (bigcone Douglas fir).

Biology.

Scolytus oregoni colonizes large limbs and tops of its host and also fresh slash ( Edson 1967; Smith, pers. obs.).

The adult gallery is typically constructed parallel to the grain of the wood and has a central nuptial chamber (Fig. 24). The gallery structure is typically bayonet shaped but may also be longitudinal. Each egg gallery extends in opposite directions to the grain of the wood from the central nuptial chamber. The nuptial chamber is transverse to the egg galleries. The adult gallery deeply scores the sapwood and lightly scores the cambium. The adult gallery averages 6.0-18.0 cm in length. Egg niches are closely spaced and deeply score the sapwood. Larvae extend their mines perpendicular to the egg gallery in a fan shaped pattern before terminating in pupation chambers, which are constructed in the sapwood ( Edson 1967).

Remarks.

Specimens of Scolytus oregoni are very rarely collected and the species is perhaps the least common of the conifer-feeders in the United States. There are many gaps that occur in its distribution range, particularly between northern and southern California. Considerable variation is observed in the male ventrite 1 and 2 across the geographic range especially between northern California, Oregon and Washington and southern California. Southern California populations colonize Pseudotsuga macrocarpa while individuals from the rest of the range colonize Pseudotsuga menziesii . In addition, Scolytus oregoni males from California and particularly southern California have a greater impression of the second ventrite and thicker margin between ventrite 1 and 2 to specimens from Oregon and Washington.