Scolytus robustus Blackman, 1934

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 47-50

Taxon classification Animalia Coleoptera Curculionidae

Scolytus robustus Blackman, 1934 Figs 52-53

Scolytus robustus Blackman, 1934: 19.

Diagnosis.

The Scolytus robustus male is quite distinctive with its strongly flattened frons, apical margin of ventrite 1 strongly, acutely produced forming a lip along the base of ventrite 2, basal margin of ventrite 2 appearing impressed and by the unarmed apical margin of ventrite 2. The female is morphologically similar to that of Scolytus ventralis . The Scolytus robustus female is distinguished by having the apical margin of ventrite 1 forming a carinate lip along the basal margin of ventrite 2.

Description (male).

2.5-4.0 mm long (mean = 3.2 mm; n = 20); 1.8-2.7 times as long as wide. Head, pronotum and abdominal venter dark red-brown, antennae light brown, legs dark red-brown to light brown, elytra red-brown. Pronotum typically darker than elytra.

Head. Epistoma moderately emarginate; epistomal process strongly developed and elevated; 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 small, coarse; moderately and 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 sharply 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, weakly serrate apex; apex moderately emarginated at suture. Margin of apical edge bearing large, coarse punctures. Disc smooth, shining; interstriae not impressed, more than twice width of striae, interstrial punctures uniseriate, smaller than those of striae, bearing minute, recumbent setae less than length of a puncture; striae weakly impressed. Declivity bearing sparse, short, erect yellow setae. Metepimeron half-length of metanepisternum.

Venter. Apical margin of ventrite 1 strongly, acutely produced forming lip along base of ventrite 2, basal margin of ventrite 2 appearing impressed. Ventrite 2 nearly perpendicular to ventrite 1; surface glabrous, shining, rugose, finely punctate; punctures small, fine, shallow; surface flattened, unarmed or with weak median tumescence on apical margin; 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 or median depression is absent.

Female.

2.2-4.1 mm long (mean = 3.2 mm; n = 20); 1.9-2.5 times as long as wide. Similar to male except epistoma feebly emarginate, epistomal process less strong ly developed and elevated, 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.

Specimens examined.

143.

Type material.

Holotype Scolytus robustus Blackman: male, labeled "Prescott N.F. Ariz., VII-24-[19]30, M.W. Blackman Collector, Abies concolor , Hopk. US 20410E, Type No. 43835 USNM" (USNM).

Non-type material.

UNITED STATES:ARIZONA: [Coconino Co.]: Grand Canyon North Rim, Kaibab National Forest, VI.[19]66, [L. Edson] (EMEC-4). [Graham Co.]: Pinaleno Mountains, Swift Trail, 3 mi, Lady Bug Saddle, 11.IX.1964, C.W. O’Brien, ex. Abies sp. (CASC-1, CNCI-4, EMEC-2); Coronado National Forest, SR 366, N32°37.702', W109°49.472', 7896 ft, 24.V.2010, S.M. Smith, ex. Abies concolor (MSUC-2). COLORADO:Costilla Co.: near Fort Garland, Forbes Trinchera Ranch, VII-VIII.1976, D. Leatherman ex. white fir [= Abies concolor ] (CSUC-1). Huerfano Co.: near Red Wing, 16.VII.1975, D. Leatherman, ex. white fir [= Abies concolor ] (CSUC-4). Pass Creek, 20.VIII.1975, D. Leatherman, ex. white fir [= Abies concolor ] (CSUC-2). La Plata Co.: Columbine Lake, 11.VIII.2004, D. Leatherman, ex. subalpine fir [= Abies lasiocarpa ] (CSUC-1). NEVADA:Clark Co.: 19.VII.[19]29, C.C. Searl (DEBC-1, EMEC-4). Cathedral Rock, emerged 7-9.V.2002, R. Turnbow, ex. Abies sp. (WFBM-2). White Pine Co.: Baker, 17.V.1939, T.O. Thatcher (CNCI-2). NEW MEXICO:Bernalillo Co.: Cibola National Forest, Sandia Peak, 9.VII.[19]68, D.E. Bright (CNCI-1); NM536, N35°12.853', W106°24.743', 8753 ft, 10.V.2010, S.M. Smith, A.I. Cognato, ex. Abies concolor (MSUC-15), N35°11.655', W106°24.075', 8317 ft (MSUC-30). [Santa Fe Co.]: Santa Fe, Little Teseque Canyon, 14.VI.[19]35, Van Dyke (CASC-3). [Unspecified County]: Sandia Mountains, tree 9, 29.V.1969, S.L. Wood, ex. Abies concolor (MSUC-13), tree 18, 30.V.1969 (MSUC-19). TEXAS: [Unspecified county]: San Antonio, Hopk. U.S. 3938, W.F. Fiske, ex. bred 15.VI.[19]07 (USNM-3). UTAH:Cache Co.: Logan (CNCI-1). [San Juan Co.]: Mount Navajo, 8500 ft, 10.VI.[19]36, McAbee (CASC-4). Utah Co.: Payson Canyon, 14.V.1960, D.E. Bright, ex. Abies concolor (CNCI-3); 20.V.1961, S.L. Wood, ex. Abies concolor (USNM-9). [Unspecified County]: Bryce Canyon National Park, 10.V.1981, M.M. Furniss, ex. Abies concolor (WFBM-10). UNSPECIFIED STATE: (CASC-1).

Distribution.

UNITED STATES: Arizona, Colorado, Nevada, New Mexico, Texas, Utah (Fig. 34).

Hosts.

Principal host: Abies concolor (Gord. & Glend.) Lindl. ex Hildebr (white fir). Incidental host: Abies lasiocarpa (Hook.) Nutt (subalpine fir).

Biology.

Scolytus robustus is found in the limbs and tops of its host and fresh slash. Galleries are often initiated near limb bases ( Edson 1967).

The adult gallery contains two egg galleries that branch from the central nuptial chamber. Gallery shape is quite variable and ranges from ‘S’ shaped at an oblique angle to the grain to nearly perpendicular against the grain (Fig. 25). Typically one egg gallery obliquely extends from the central nuptial chamber against the grain of wood for a short distance before becoming apically recurved. The second egg gallery is identical to the first but runs in the opposite direction. However galleries may extend perpendicular to the grain of the wood or may not be apically recurved. The adult gallery deeply scores the sapwood and ranges in size from 2.5-7.0 cm in length. Egg niches are distinct, score the sapwood and are closely spaced along the egg galleries. Larval mines rapidly diverge perpendicular to the adult gallery and are parallel to the grain of the wood. Larval mines terminate in pupation chambers that score the sapwood ( Edson 1967).

Collection notes.

The senior author collected this species from 10.0 cm diameter slash with thick (5.0 mm) bark.

Remarks.

A relatively large amount of intraspecific variation (0.0537) was observed in mitochondrial COI sequences from specimens collected from Arizona and New Mexico and low variation observed between the two Arizona populations (Table 6). Scolytus robustus only occurs on Abies . In southeastern Arizona, Abies spp. and Scolytus robustus are confined to high elevation sites on the sky islands. These Arizona populations are isolated from the New Mexico populations by large areas that are unsuitable for Abies . No specific geographic morphological differences were observed among the examined specimens.