Pachysquamus subcostulatus ( Mannerheim, 1853 ) Mannerheim, 1853

Mercado-Vélez, Javier E. & Negrón, José F., 2014, Revision of the new world species of Hylurgops LeConte, 1876 with the description of a new genus in the Hylastini (Coleoptera: Scolytinae) and comments on some Palearctic species, Zootaxa 3785 (3), pp. 301-342 : 311-314

Pachysquamus subcostulatus ( Mannerheim, 1853) comb. n.

( Figures 2 a, 3a, 4a, 6a, 7a, 9a–b, 10)

Hylastes subcostulatus Mannerheim, 1853:239 . (Kenai Peninsula, Alaska, USA, lost) H. cristatus Mannerheim, 1853:239 (Kenai Peninsula, Alaska, USA, lost) H. alternans Chapuis, 1869:22 (unspecified locality, Mexico) Hylurgops subcostulatus, LeConte, 1876:389

H. cristatus, LeConte, 1876:389

H. alternans, Swaine, 1909:116

Hylastes (Hylastes) cristatus, Hagedorn, 1910:45 H. (Hylurgops) subcostulatus, Hagedorn, 1910:46 H. subcostulatus subcostulatus, Wood, 1982:91 H. subcostulatus alternans, Wood, 1982:91

Diagnosis. Distinguished from all other species in the Hylastini by the strongly elevated odd numbered elytral interstriae Fig. 9 a), by the dense dorsal cover of cup-shaped setae ( Fig. 9 b), the strongly pointed anterior margin of the mesoventrite, and by the more elongate aedeagus.

Description. Size. Length 3.1–4.7 (avg. 4.0 ± 0.4) mm long, 2.7× longer than wide. Color. Mature adult dorsal color brownish red, ventral sclerites dark reddish-brown. Frons. Mid-frontal impression deep, becoming deeper from convex area below eyes towards epistoma, surface evenly punctate, inter-puncture spaces half the width of a puncture, shiny; carina elevated, short, shiny if present, extending from below the vertical impression to epistoma; epistomal lobe narrow; vestiture consists of hair-like setae, longer below middle, length of 2–7× the diameter of a puncture. Pronotum. Broad, 0.9–1.0 (avg. 0.9 ± 0.3)x as long as wide, distinctly constricted anteriorly ( Fig. 9 c), widest near basal fourth, sides of basal fifth slightly elevated forming a narrow margin, sides rounded at middle, constricted on anterior fifth; dorsal median line sometimes present, if so extending anteriorly from base to fourfifths of pronotum, surface shiny, slightly raised, usually concealed by cup-shaped setae; interspaces evenly, minutely punctate, punctures separated by distance equal to ⅓ diameter of large punctures, margin smooth, shiny, and usually concealed by cup-shaped setae; additional vestiture consisting of sparse, erect bristles, 3× length of large discal punctures, longer at marginal areas. Elytra. Length/width ratio 1.7–1.9 (avg. 1.8 ± 0.1); anterior margin distinctly procurved, crenulate marginal line distinct and elevated; striae shallowly impressed, increasing from narrower than interstriae near base to wider at declivity, with deep, round punctures with shiny surfaces, less than their diameter apart; discal interstriae smooth, shiny, minutely punctate (seen at 100× or more), concealed by cup-shaped setae, single midline of erect bristles separated by distance of two strial punctures, rising behind interstrial granules, as long as a discal puncture diameter. Declivity. Convex, alternate interstriae strongly elevated ( Fig. 9 a), with large tubercles as wide or wider than rest of interstrial costa; vestiture consisting of a bristle rising behind each granule, 1–3× as long as strial puncture and a ground surface cover of dense, recumbent, cup-shaped setae. Ventral sclerites. Glossy, punctured. Legs. Tarsi dark reddish-brown; protibiae with two large socketed teeth before apical angle; meso- and metatibiae with one or two large socketed teeth before apical angle; third tarsal segment slightly broader than second. Aedeagus. Apodemes proportionally shorter than aedeagus in contrast to those in New World species of Hylurgops ( Figs. 7 b–i). Aedeagus elongate cylindrical, ventrally straight ( Fig. 6 a), barely arcuate dorsally. Without neck-like extension ( Fig. 6 c) of apodemes base ( Fig. 6 a) ( Grocholski et al. 1976). Tegmen with a short manubrium.

Gallery: The maternal gallery is longitudinal, uniramous ( Hopkins 1902), slightly sinuate ( Fig. 3 a). Eggs are laid in only one side of the gallery from which larval galleries run perpendicular to that side only ( Cibrián-Tovar et al. 1995).

Material examined. 850 specimens from the CNCI, CSUC and the USNM collections were examined. CANADA. British Columbia: Coldwater ( CNCI), Midday Valley, Merritt ( CNCI), Peachland ( CNCI), Summerland ( CNCI), Vancouver ( CNCI). MEXICO. Chiapas: 5 mi. E San Cristobal ( CNCI), 6 mi. SE San Cristobal ( CNCI), San Cristobal ( CNCI). Chihuahua: Mesa del Huracan ( CNCI). Durango: 3 mi. E El Salto ( CNCI), 7 mi. W El Salto ( CNCI), 10 mi. SW El Salto ( CNCI), 10 mi. W El Salto ( CNCI), 11 mi. W El Salto ( CNCI), 11 mi. SW El Salto ( CNCI), Buenos Aires, 10 mi. W La Ciudad ( CNCI). Mexico City ( CNCI, DEBC). Nuevo Leon: Cerro Potosi ( CNCI), NE slope Cerro Potosi, Mpio. Galaena ( CNCI). Puebla: 14 mi. W Texmelucan ( DEBC), km 60 Rd Mexico-Puebla ( CNCI), Zoquiapan NF ( CNCI). USA. Arizona: Apache Co.: Brady Springs, SE Vernon, Sitgreaves NF ( UAIC); Cochise Co.: Barfoot Grds. ( DEBC), Barfoot picnic Grds., Chiricahua Mountains ( CNCI, DEBC); Coconino Co.: 10 mi. SW Flagstaff ( CNCI); Graham Co.: Mount Graham ( CNCI), Pinaleño Mountains ( CNCI); Greenlee Co.: Hannagan Camp ( CNCI), 15 mi. S Alpine ( CNCI); Pima Co.: Mount Lemmon, Sta. Catalina Mountains ( CNCI), Sta. Catalina Mountains ( CNCI), Bear Canyon, Chiricahua Mountains ( CNCI); Yavapai Co.: Prescott NF, Prescott ( CNCI). California: El Dorado Co.: 10 mi. E Georgetown, Blodgett Forest, UC ( CNCI), 3 mi. E Kyburz ( CNCI), Fallen Leaf Lake ( CNCI, DEBC), Placerville ( CNCI, DEBC), El Dorado NF ( CNCI); Madera Co.: Chiquito Basin ( CNCI); Modoc Co.: Hackamore ( DEBC), Modoc NF ( CNCI); Placer Co.: Big Bend Ranger Sta. ( DEBC); San Bernardino Co.: Big Bear Lake ( CNCI); San Diego Co. ( CNCI).

Colorado: Bent Co.: Las Animas Co. ( CSUC); Chaffee Co.: CR-386 N Buena Vista ( CSUC), Droney Gulch, Salida ( CSUC); Douglas Co.: Franktown ( CSUC); El Paso Co.: Black Forest ( CSUC); La Plata Co.: Electra Lake ( CSUC); Larimer Co.: Buckhorn Canyon ( DEBC), Poudre Canyon ( DEBC); Montezuma Co.: Dolores FS Rd 527 ( CSUC), Mancos ( CSUC); Montrose Co.: Sanborn Pk. ( CSUC). Idaho: Kootenai Co.: near Coeur d' Alene ( CNCI); Latah Co.: Deary ( CNCI). Montana: Lake Co.: Pablo ( CNCI); Ravalli Co.: Hamilton ( CNCI). New Mexico: Otero Co.: Cloudcroft ( CNCI). Oregon: Josephine Co.: Oregon Caves Nat’l Monument ( CNCI), Klamath Co.: Ft. Klamath ( CNCI). South Dakota: Custer Co.: Bear Mountain area Black Hills NF ( RMRS), Pennington Co.: Rushmore Mt. Black Hills ( CNCI). Utah: Garfield Co.: Panquitch Lake, Dixie NF ( CNCI, DEBC); Juab Co.: The Mammoth ( CNCI); Ouray Co.: Long Hollow, Dixie NF ( DEBC); Sevier Co.: Pin Hollow, Fish Lake ( CNCI, DEBC). Washington: Walla Walla Co.: Kooskooskie ( CNCI).

Hosts. Picea engelmannii , P. pungens , Pinus arizonica var. cooperi , P. ayacahuite , P. contorta , P. duranguensis , P. engelmannii , P. hartwegii , P. jeffreyi , P. lambertiana , P. leiophylla , P. leiophylla var chihuahuana , P. montezumae , P. ponderosa , P. pseudostrobus , P. strobiformis , P. teocote , Pseudotsuga menziesii , and Tsuga heterophylla .

Distribution ( Fig. 10 ). NORTH AMERICA: British Columbia, Canada to Chiapas, Mexico and the Black Hills of South Dakota. There is only one known record from the Kenai Peninsula of Alaska, the putative type locality ( Mannerheim 1853).

Discussion. Hylastes subcostulatus was described by Mannerheim (1853) from a single specimen collected by Dr. Fredrick Frankenhaeuser from the Kenai Peninsula in Alaska as part of an early Russian expedition. Another specimen in the same collection was described as Hylastes cristatus by Mannerheim (1853) and later synonymized with H. subcostulatus by Wood (1982).

The lack of collection records between British Columbia and the Mannerheim type from the Kenai Peninsula is intriguing. The type specimens of both H. subcostulatus and H. cristatus are considered lost ( Wood 1969, 1982). Subsequent re-descriptions, including those of LeConte (1868) and Chapuis ( H. alternans, 1869 ) were made from specimens collected from British Columbia and Mexico, respectively; however, the original description by Mannerheim is adequate to identify the species. The possibility that the type specimen was mislabeled should be considered.

Wood (1982) recognized H. alternans as a subspecies of H. subcostulatus based on what he considered to be a population with more elevated declivital interstriae and, in these, more inflated tubercles in specimens occurring south of central Arizona in contrast to specimens occurring north of that area. The subspecific concept has been questioned (D.E. Bright pers. comm.) based on the uninterrupted distribution of both geographical forms. Examination of specimens from throughout the species’ range suggests that the size of the tubercles and the elevation of interstriae are variable and do not correlate with the arbitrary geographical distribution of the subspecies considered by Wood (1982).

Pachysquamus subcostulatus ranges from the Canadian Cascades in southern British Columbia to the Sierra de Chiapas in southern Mexico. The Black Hills of South Dakota represent the easternmost limit of the species. Ignoring the questionable Kenai specimens, the northern distribution of P. subcostulatus corresponds with that of P. ponderosa . The species occurs from altitudes of 60–700 m in Canada. In the continental United States, it occurs from elevations of 60–3,300 m. Although it primarily attacks P. ponderosa , it occurs in other conifers in the genera Pinus , Picea , Pseudotsuga , and Tsuga . In Mexico, examined specimens were collected from elevations ranging from 2,300–3,700 m.

As with other members in the Hylastini , P. subcostulatus selects and develops in conifers that have been weakened or killed by other bark beetles such as Dendroctonus or by other natural or anthropogenic agents such as severe drought and fires.

Figures

FIGURE 2. Anterior margin of mesoventrite in the Hylastini: a) distinctly pointed (Pachysquamus subcostulatus), b) slightly rounded and sub-inflated (Hylurgops planirostris), c) truncate, margin straight (Hylastes salebrosus).

FIGURE 3. Detail of Hylastini galleries: a) Pachysquamus subcostulatus, maternal (red) and larval gallery (adapted from Cibrián-Tovar et al. 1995), b) Hylurgops pinifex (eastern form), maternal (red) and larval gallery (adapted from Blackman 1919).

FIGURE 6. Aedeagus and spiculum gastrale: a) Pachysquamus subcostulatus, b) Hylurgops reticulatus, c) Hylastes ater (modified from Grocholski et al. 1976), d) Hylurgops rugipennis.

FIGURE 7. Aedeagus of the New World Hylurgops and Pachysquamus: a) Pachysquamus subcostulatus, b) Hylurgops planirostris, c) H. rugipennis, d) H. pinifex, e) H. incomptus, f) H. longipennis, g) H. knausi, h) H. reticulatus, and i) H. porosus.

FIGURE 9. External characters of Pachysquamus subcostulatus: a) declivity showing elevated interstriae, b) cup-shaped setae (elytral disc shown), c) deep anterior constriction of prothorax.

FIGURE 10. Distribution of Pachysquamus subcostulatus showing location of Mannerheim’s lost types on the Kenai Peninsula, Alaska (insert).