Scolytus monticolae (Swaine, 1917)

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 36-37

Taxon classification Animalia Coleoptera Curculionidae

Scolytus monticolae (Swaine, 1917) Figs 29, 37

Eccoptogaster monticolae Swaine, 1917: 32.

Scolytus monticolae (Swaine, 1917): Keen 1929: 13.

Diagnosis.

Scolytus monticolae males are easily confused with Scolytus reflexus males, especially those exhibiting the wickhami phenotype. They are easily distinguished by the size of male ventrite 5. In Scolytus monticolae , ventrite 5 is equal in length to width of ventrites 3 and 4 combined. In Scolytus reflexus , ventrite 5 is equal in length to ventrite 4. Scolytus monticolae lacks an epistomal process while Scolytus reflexus typically has a strongly developed epistomal process. Males are distinguished from those of Scolytus tsugae by the following combination of characters: surface of ventrite 2 shining but minutely reticulate; elytral striae not impressed; basal margin of ventrite 2 more pronounced and produced laterally; elytral strial punctures small, spaced 2-3 diameters of a puncture. Females of Scolytus monticolae are distinguished from Scolytus reflexus females by having the apical margin of ventrite 1 weakly produced, never rounded and the surface of ventrite 2 smooth and flat, and are separated from those of Scolytus tsugae by elytral discal striae not impressed and ventrite 2 shining in luster.

Description (male).

2.5-3.0 mm long (mean = 2.9 mm; n = 10); 2.0-2.5 times as long as wide. Head, pronotum, and abdominal venter dark red-brown, legs light brown, antennae yellow-brown, elytra usually dark red-brown but may be brown. Pronotum typically darker than elytra.

Head. Epistoma weakly emarginated; 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; weakly aciculate-punctate, medial area appearing shagreened; aciculations converging at epistoma; punctures small, coarse; sparsely, 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 basal 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, twice width of striae, punctures uniseriate, smaller than those of striae, bearing minute, recumbent setae length of interstrial punctures (may be abraded); striae not impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron less than half-length of metanepisternum.

Venter. Apical margin of ventrite 1 weakly elevated above base of ventrite 2, more pronounced and produced laterally forming two cups. Ventrite 2 nearly perpendicular to ventrite 1; surface smooth, shining, finely punctate; punctures small, fine, shallow; surface flattened, depressed above basal margin; apical margin unarmed; covered in recumbent setae twice width 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 less than combined lengths of ventrites 3 and 4; setal patch and median depression absent.

Female.

2.3-3.5 mm long (mean = 3.0 mm; n = 10); 2.3-2.7 times as long as wide. Similar to male except epistoma feebly emarginated, frons convex when viewed laterally, strigate, setae sparser, shorter, less than width of eye; weakly transversely impressed between inner apices of eyes. Second ventrite unarmed. Length of ventrite 5 greater than combined lengths of ventrites 3 and 4.

Specimens examined.

123.

Type material.

Lectotype: female, labeled "[Arrowhead, British Columbia], Pinus monticola , 2423, J.M. Swaine Coll, female" (CNCI). Lectotype designated Bright 1967: 674.

Non-type material.

CANADA:BRITISH COLUMBIA: Merritt, Midday Valley, 27.VI.1926, W. Mathers (USNM-2), 4.IX.1926 (USNM-2). Trinity Valley, 4.VII.1954, ex. Pseudotsuga taxifolia (USNM-4). UNITED STATES:COLORADO:Custer Co.: Hillside, 6 mi W., Duckett Creek, FR331, Rita Alta Fuelwood area, 23.V.2000, D. Leatherman (CSUC-1). [Garfield Co.]: Glenwood Springs (CASC-1). Jefferson Co.: Buffalo Creek, 6.VIII.2004, D. Leatherman, ex. Douglas fir [= Pseudotsuga menziesii ] (CASC-2). IDAHO:Benewah Co.: St. Maries, Hopk. U.S. 618074, 28.VIII.1978, M.M. Furniss, ex. Pseudotsuga menziesii (USNM-32). Boise Co.: Boise National Forest, Bogus Basin, Bogus Basin Rd, N43°44.347', W116°07.099', 6047 ft, 8.VIII.2010, S.M. Smith, A.R. Gillogly, ex. Pseudotsuga menziesii (MSUC-8). Bonner Co.: Priest River Experimental Forest, Hopk. U.S. 61809-A, 25.X.1978, M.M. Furniss, ex. Pseudotsuga menziesii (USNM-26). Kootenai Co.: Coeur d’Alene, 30.VIII.1919, J.C. Evenden (MSUC-12); 7.VIII.1919, J.C. Evenden, ex. Pseudotsuga menziesii (MSUC-4). Shoshone Co.: Coeur d’Alene National Forest, N47°25.708', W115°53.464', 3728 ft, 15.VIII.2010, S.M. Smith, A.R. Gillogly, ex. Pseudotsuga menziesii (MSUC-19). Prichard, 23.VII.1920, J.C. Evenden, ex. Abies grandis (MSUC-2). MONTANA: [Sanders Co.]: Trout Creek, 1.VIII.1981, J. Dunkel, ex. Douglas fir (USNM-2). OREGON: [Unspecified County]: Santiam National [State] Forest, 22.VIII.[19]14, W.J. Chamberlin, ex. Abies amabalis (EMEC-1). WASHINGTON: [Kittitas Co.]: Easton (USNM-1). [Yakima Co.]: Cliffdell, 7.VII.[19]35, R.H. Beaner (USNM-1). WYOMING: [Park Co.]: Cody, Hopk. U.S. 34220-F, 10.V.[19]56, H.E. Ostmark, ex. Pseudotsuga taxifolia [= Pseudotsuga menziesii ] (CSUC-2).

Distribution.

CANADA: British Columbia. UNITED STATES: Colorado, Idaho, Montana, Oregon, Utah, Washington, Wyoming (Fig. 38).

Hosts.

Pseudotsuga menziesii (Mirb.) Franco (Douglas fir).

Biology.

Scolytus monticolae commonly infests the bole, suppressed branches and fresh slash of Douglas fir. Scolytus monticolae (as Scolytus tsugae , see remarks below) has been reported to kill drought stressed sapling and pole-sized Douglas fir trees in British Columbia ( McMullen and Atkins 1959) and Wyoming ( Furniss and Carolin 1977).

Adult galleries strongly resemble those of Scolytus reflexus , parallel to the grain of the wood, bayonet shaped and consist of two egg galleries and a central nuptial chamber (Fig. 24). From the central nuptial chamber, one egg gallery extends with the grain of the wood and the other egg gallery is slightly transversely extended and then is extended parallel to the grain. The nuptial chamber is oblique to the egg galleries. The adult gallery scores the sapwood more than the cambium and averages 5.0-9.0 cm in length. Egg niches are generally placed in pairs along the egg galleries and score the sapwood. Larvae extend their mines perpendicular to the egg gallery before diverging in a fan shaped pattern. Pupation may occur under the bark or in the sapwood. In Idaho, Scolytus monticolae has one generation per year with flight occurring in July ( Furniss and Johnson 2002; Smith, pers. obs.). Broods overwinter as larvae and emerge the following summer ( Edson 1967; Furniss and Johnson 2002).

Collection notes.

The senior author found this species to be common in suppressed limbs and slash in Idaho.

Remarks.

The lectotype does not bear a locality label. Swaine’s (1917) description states the lectotype was collected at Arrowhead, British Columbia.

In their paper describing the biology of Scolytus tsugae , McMullen and Atkins (1959) considered Scolytus monticolae a synonym of Scolytus tsugae based on correspondence with G.R. Hopping (page 417). Wood (1966: 30) formally synonymized Scolytus monticolae with Scolytus tsugae , and later removed the species from synonymy ( Wood 1982; M.M. Furniss, pers. comm.). However, Wood (1982) did not explicitly state that he was the author that recognized the species. These two species are closely related and have subtle morphological differences. This has led to a confusing account of both species in the literature. The majority of which seems to be applicable to Scolytus monticolae rather than Scolytus tsugae . The above diagnostic characters and different biologies readily differentiate the species.