Scolytus laricis Blackman, 1934

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 35-36

Taxon classification Animalia Coleoptera Curculionidae

Scolytus laricis Blackman, 1934 Figs 29, 35

Scolytus laricis Blackman, 1934: 24.

Diagnosis.

Scolytus laricis is very morphologically similar to Scolytus fiskei and Scolytus unispinosus . Males are distinguished from those of Scolytus fiskei by the dull appearance of abdominal ventrite 2 and by the frons densely covered by long setae. Males can be distinguished from those of Scolytus unispinosus by the following combination of characters: the base of the ventrite 2 spine extends from the apical margin to three-quarters the length of the segment and host genus. The female is distinguished from that of Scolytus fiskei by the dull luster of ventrite 2 and is distinguished from that of Scolytus unispinosus by the frons moderately and coarsely aciculate-punctate; ventrite 1 rounded over onto surface of ventrite 2, not forming an obtuse angle, and the base of ventrite 2 finely impressed.

Description (male).

2.3-4.0 mm long (mean = 3.1 mm; n = 15); 1.8-2.5 times as long as wide. Head, pronotum, and abdominal venter dark red-brown to black, elytra and legs light brown, antennae yellow-brown. Pronotum typically darker than elytra.

Head. Epistoma weakly emarginated; epistomal process present, moderately developed and elevated; median area above mandibles bearing dense patch of long yellow hair-like setae. Frons appearing flattened when viewed laterally from epistoma to vertex, moderately transversely impressed just above epistoma to vertex; strongly, coarsely, longitudinally aciculate-punctate; aciculations converging at epistoma; punctures sparse, large, coarse; moderately to densely 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 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 smooth, shining; interstriae not impressed, twice width of striae, punctures uniseriate, smaller than those of striae, bearing minute, recumbent setae length of interstrial punctures (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 on ascendant part of venter. Ventrite 2 nearly perpendicular to ventrite 1; surface smooth, shining, finely punctate; punctures small, fine, shallow; covered with sparse setae less than length of segment 3; surface convex; apical margin armed with laterally compressed, median spine with base extending from apical margin to ¾ length of segment, apex rounded, rarely a slightly elevated vertical carina (Oregon: Dixie Pass and Frog Lake) instead of spine; lateral margins of ventrites 2-3 and ventrite 4 unarmed. Ventrite 5 carinate ridge equidistant between basal and apical margins of segment; length of ventrite 5 less than combined lengths of ventrites 3 and 4; setal patch and median depression absent.

Female.

2.6-4.0 mm long (mean = 3.2 mm; n = 15); 2.1-2.9 times as long as wide. Similar to male except epistoma feebly emarginated, epistomal process weakly developed, frons convex when viewed laterally, weakly longitudinally aciculate, setae sparser, shorter, less than width of eye; weakly transversely impressed just above epistoma. Second ventrite apical margin armed with a blunted median denticle, with base extending from apical margin to a third length of segment. Ventrite 5 length greater than combined lengths of ventrites 3 and 4.

Specimens examined.

294.

Type material.

Holotype Scolytus laricis Blackman: male, labeled "[Cedar Mountain, Moscow, ID] Hopk. US 225d, 8636 m [sic!], 6-20-[18]99, Type No. 43839" (USNM).

Non-type material.

CANADA:BRITISH COLUMBIA: Canoe, 12.VII.1933, A. Thrupp, ex. Larix occidentalis (CASC-3). Rossland, 21.IX.[19]61, D.E. Bright, ex. Larix laricina (CNCI-2). UNITED STATES:IDAHO:Boundary Co.: [Idaho Panhandle National Forest], Robinson Creek campground, N48°58.197', W116°13.068', 2748 ft, 10.VIII.2010, S.M. Smith, [A.R. Gillogly], ex. Larix occidentalis , emerged II.2011, M.M. Furniss (MSUC-94). Clearwater Co.: Elk River, V.1981, M.M. Furniss, ex. Larix occidentalis (WFBM-17), VII.1981 (WFBM-11). Elk River, 13 mi S.W., Hopk. U.S. 60361-A, 23.IV.1975, M.M. Furniss, ex. Larix occidentalis (WFBM-4). Idaho Co.: Salmon Mountain, 18.VIII.1985, M.M. Furniss, J.B. Johnson, ex. Larix lyalli (WFBM-29). Kootenai Co.: Coeur d’Alene, Hopk. U.S. 16306-B, 2.VIII.1919, J.C. Evenden, ex. Larix occidentalis (WFBM-9), 8.VIII.1919 (MSUC-11). Deception Creek Experimental Forest, Hopk. U.S. 58889-A, 10.VII.1968, M.M. Furniss (OSAC-4), Hopk. U.S. 53376, 11.VII.1968 (WFBM-2), Hopk. U.S. 60320, 25.VII.1968, (OSAC-2), Hopk. U.S. 50421-B,C, 1.VII.1975 (OSAC-2), Hopk. U.S. 60356, 30.VII.[19]68, M.M. Furniss, ex. Larix occidentalis (WFBM-6). Latah Co.: Moscow, 2.VIII.1930, 2560 ft, P. Rice, ex. trap (WFBM-1). Moscow Mountain, Hopk. U.S. 53632-F, 23.VI.1964, M.M. Furniss, ex. in flight (WFBM-1), Hopk. U.S. 60421-A, 1.VII.1975 (OSAC-1). MONTANA:Missoula Co: Missoula, 35 mi N.W., 3.XI.[19]65, ex. Larix occidentalis (WFBM-2). Nine Mile Creek, Hopk. U.S. 48830, 3.XI.1965, M.M. Furniss, ex. Larix occidentalis (WFBM-2, OSAC-1). Ravalli Co.: [Bitterroot Mountains], Trapper Peak, 2.X.[19]88, M.M. Furniss, ex. Larix lyalli (WFBM-3). [Unspecified County]: Libby, 60 mi S.E., 30.VI.[19]72, D.E. Bright, ex. Larix laricina (CNCI-7). OREGON:Crook Co.: Summit Prairie, 12.VI.1940, Schuh, Scott, ex. Larix occidentalis (CNCI-3, EMEC-2). [Grant Co.]: Dixie Pass, Malheur National Forest, 23.VI.1961, S.L. Wood, J.B. Karren, D.E. Bright, ex. Larix occidentalis (CNCI-6, USNM-6). Jefferson Co.: Camp Sherman, T.O. Thatcher, ex. Larix lyalli limbs (CSUC-10), 9.VII.[19]66, [L. Edson], ex. Larix lyalli (CNCI-2). Suttle Lake, 4 mi N., 25.VII.1939, ex. Larix lyalli (CSUC-1); 28.VII.1939, F. Grey, J. Schuh, ex. Larix occidentalis (CASC-1, FMNH-6, MSUC-1, OSAC-14), W.J. Chamberlin, ex. Larix lyalli (EMEC-7, WFBM-3). Suttle Lake, 4 mi W., 15.VIII.1939, Schuh, Scott (MSUC-1). [Marion Co.]: Clear Lake, 17.VIII.[19]51, R. Kangur, ex. larch [= Larix sp.] (EMEC-4, WFBM-2). [Umatilla Co.]: Tollgate, 28.X.1948, C. Chastain, ex. Larix occidentalis (EMEC-1). [Wasco Co.]: [Mount Hood National Forest] Frog Lake [campground], 4S9 E17, 2.VIII.1951, R. Kangur (CNCI-3). WASHINGTON:Okanogan Co.: Disautel, 4.XI.1936, R.L. Furniss, ex. Larix occidentalis (OSAC-3). [Pend Oreille Co.]: Metaline Falls, Hopk. U.S. 19905, 20.VII.1930, D. DeLeon, ex. Larix occidentalis (OSAC-2, WFBM-1). [Stevens Co.]: Northport, 18.VII.1929, R. Hopping (OSAC-1). [Unspecified County]: Mount Adams, 7000 ft, Hopk. U.S. 53359-C, 2.VIII.1968, M.M. Furniss, ex. on snowfield (WFBM-1).

Distribution.

CANADA: British Columbia. UNITED STATES: Idaho, Montana, Oregon, Washington (Fig. 36).

Hosts.

Larix occidentalis Nutt. (western larch) and Larix lyalli Parl. (subalpine larch).

Biology.

Scolytus laricis prefers to colonize suppressed lower limbs of its host and fresh slash.

The adult gallery is parallel to the grain of the wood and consists of two egg galleries and a central nuptial chamber (Fig. 24). The central nuptial chamber extends at a right angle to the rest of the gallery and opposite the nuptial chamber is a rounded turning niche. This gives the central part of the gallery an ovoid appearance that is different from all other Nearctic Scolytus . Egg galleries are extended parallel to the grain of the wood. The adult gallery scores the sapwood more deeply than the cambium, and ranges in length from 6.4-11.5 cm. The female constructs widely spaced egg niches on both sides of each egg gallery. Larval mines extend against the grain of wood and gradually diverge before terminating at pupation chambers that deeply score the sapwood ( Edson 1967; Furniss and Johnson 2002). There is one generation per year and broods overwinter as larvae ( Furniss and Johnson 2002).

Collection notes.

Scolytus laricis was collected four times by the senior author and each time specimens were collected from fresh broken branches that were less than 5.0 cm in diameter with bright green needles. Specimens were also collected from a fallen Larix occidentalis of 15.0 cm DBH.

Remarks.

Furniss and Johnson (2002) reported that specimens collected from Larix lyalli create a different gallery structure than those collected from Larix occidentalis (M.M. Furniss pers. comm.). The galleries on Larix lyalli are "shorter, less uniform, and with the entrance chamber often extended a short distance to the sides of the gallery" ( Furniss and Johnson 2002). Specimens from Larix lyalli could not be collected during the coarse of our investigation. We noticed slight morphological variation among some populations but were unable to determine if the differences represent species limits. Further study is needed to address this question.

The holotype of Scolytus laricis does not bear a locality label. Blackman’s (1934) description states A.D. Hopkins collected the holotype on Cedar Mountain near Moscow, Idaho. Numerous collectors listed in the material examined reported this species as collected from Larix lyalli in Oregon. This host species occurs east of the Cascade Range in the Wenatchee Mountains in Washington and is not known to occur in Oregon ( Burns and Honkala 1990). It is probable that the host species for these specimens was Larix occidentalis .