Scolytus obelus Wood, 1962

Smith, Sarah M. & Cognato, Anthony I., 2014, A taxonomic monograph of Nearctic Scolytus Geoffroy (Coleoptera, Curculionidae, Scolytinae), ZooKeys 450, pp. 1-182 : 38

Taxon classification Animalia Coleoptera Curculionidae

Scolytus obelus Wood, 1962 Figs 29, 41

Scolytus obelus Wood, 1962: 81.

Diagnosis.

Both sexes of Scolytus obelus strongly resemble Scolytus praeceps and are distinguished by the presence of a small median denticle on the apical margin of ventrite 2.

Description (male).

1.8-2.9 mm long (mean = 2.2 mm; n = 20); 2.1-2.9 times as long as wide. Color red brown to dark red-brown, antennae brown. Pronotum typically darker than elytra.

Head. Epistoma weakly emarginate; epistomal process weakly developed, low; 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 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, 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, weakly serrate 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 not 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. Apical margin of ventrite 1 weakly elevated above base of ventrite 2. Ventrite 2 nearly perpendicular to ventrite 1; surface shagreened, dull, finely punctate; punctures small, fine, shallow, punctures varying in size, larger and more abundant near basal margin; surface weakly concave; apical margin armed with acute median denticle; setae short, recumbent, about three times that of a puncture in length; 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.

1.7-3.0 mm long (mean = 2.3 mm; n = 20); 2.0-2.7 times as long as wide. Similar to male except epistoma feebly emarginate, epistomal process absent, frons convex when viewed laterally, weakly aciculate, setae sparser, shorter, less than width of eye; weakly transversely impressed between inner apices of eyes. Apical margin of ventrite 1 moderately elevated above base of ventrite 2. Second ventrite armed with median tumescence or minute denticle.

Specimens examined.

138.

Type material.

Holotype: male, labeled "Payson Canyon, UT, S.L Wood, 14 May 1960, Abies concolor , BLNO 001271" (USNM). Paratypes Scolytus obelus UNITED STATES:UTAH: [Beaver Co.]: Beaver, 22.IV.1950, S.L. Wood, ex. Abies concolor (USNM-4). Utah Co.: Payson Canyon, 14.V.1960, S.L. Wood, ex. Abies concolor (USNM-6), 25.VI.1962 (USNM-2).

Non-type material.

United States:Arizona:Coconino Co.: Coconino National Forest, Arizona Snow Bowl, N35°19.593', W111°42.681', 9230 ft, 27.V.2010, S.M. Smith, ex. Abies lasiocarpa [var. arizonica] (MSUC-62). Jacob Lake, 12 mi S., 31.V.1969, W. Harwood, ex. Abies concolor branch (USNM-4). Graham Co.: Pinaleno Mountains, 15.VII.1968, D.E. Bright, ex. Pseudotsuga menziesii (DEBC-3). [Coronado National Forest], [Pinaleno Mountains], Mount Graham, Hospital Flat, 9050 ft, 19.VIII.1952, H.B. Leech, J.W. Green (CASC-1), 8950 ft, 3.VIII.1965, H.B. Leech (CASC-5). Yavapai Co.: Prescott, 1 mi S., 3.VIII.1962, S.L. W[ood] (USNM-1). Prescott, 9 mi S., 5 mi E., 7800 ft, 5.VI.1969, W. Harwood, ex. Abies concolor (USNM-6). [Unspecified County]: Santa Catalina Mountains, 8500 ft, 31.V.1969 (DEBC-1, FSCA-4). COLORADO:Costilla Co.: near Fort Garland, Forbes Trinchera Ranch, VII-VIII.1976, D. Leatherman, ex. white fir [= Abies concolor ] (CSUC-4). Huerfano Co.: near Red Wing, 16.VII.1975, D. Leatherman, ex. white fir [= Abies concolor ] (CSUC-2). NEVADA:Clark Co.: Mary Jane Falls, 7900 ft, 11.VI.1969, Harwood, ex. Abies concolor (USNM-7). [White Pine Co.]: Baker, S9 T13N R69E, Mount Diablo Meridian, 17.V.1917, T.O. Thatcher, ex. Abies lasiocarpa , LCNM 39-12 (CSUC-8, USNM-1, WFBM-1). Mount Wheeler, 19.VIII.1974, S.L. Wood, ex. Abies concolor (USNM-9). NEW MEXICO: [Otero Co.]: Cloudcroft, 14-26.VII.[19]49, W.B.R. Stromberg, ex. fir tree [= Abies sp.] (USNM-1). [Unspecified County]: Sandia Mountains, 8090 ft, 29.V.1969, S.L. W[ood], ex. Abies concolor (USNM-3), 30.V.1969 (USNM-9). UTAH:Utah Co.: Provo, Payson Canyon, VIII.1964, ex. Abies concolor (EMEC-4). [Unspecified County]: Bryce Canyon National Park, Hopk. U.S. 35-043, 11.VII.1952, R. Washburn, ex. Abies concolor (EMEC-2).

Distribution.

UNITED STATES: Arizona, Colorado, Nevada, New Mexico, Utah (Fig. 27).

Hosts.

Abies concolor (Gord. & Glend.) Lindl. ex Hildebr. (white fir) and Abies lasiocarpa var. arizonica (Merriam) Lemmon (corkbark fir). Incidental host: Pseudotsuga menziesii .

Biology.

Scolytus obelus is an uncommonly encountered species. The species prefers to colonize the limbs, tops and slash of its host. Infested material ranges from 3.0-10.0 cm in diameter ( Wood 1982).

The adult gallery contains two egg galleries that branch from the central nuptial chamber. One egg gallery extends from the nuptial chamber perpendicular to the grain of wood and the second gallery extends at a 45° angle to the grain (Fig. 24). Galleries are frequently initiated near branch crotches and disguised under rough patches of bark. The adult gallery deeply scores the sapwood and lightly scores the cambium. The adult galleries range in size from 1.9-6.5 cm in length. Eggs are laid in niches on both sides of each egg gallery and larval mines radiate perpendicular to the egg gallery forming a fan shaped pattern. The larval mines gradually diverge and lightly etch the sapwood. Pupation occurs in the sapwood ( Edson 1967).

Collection notes.

The senior author collected specimens from suppressed 2.0-4.0 cm diameter branches of Abies lasiocarpa var. arizonica that had been girdled at the base by porcupines. Needles of infested branches were pale green to yellow.

Remarks.

This species is sister to Scolytus praeceps and is very similar both in morphology and gallery architecture. Interspecific divergence in COI nucleotide difference between these two taxa is quite large and averages 10.36% (Table 7).