Pachysquamus, Mercado-Vélez, Javier E. & Negrón, José F., 2014

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 : 308-311

Pachysquamus , new genus

Diagnosis. Diagnosed by the typical characters of the Hylastini ( Wood 1982) and the following: Size. Length 3.1– 4.7 (avg. 4.0 ± 0.4) mm long, 2.7× longer than wide. Color. Reddish-brown to medium dark-brown. Frons. Transverse impression between compound eyes down arching, carina extending from epistoma to frontal impression. Eyes. Elongate-oval, 2.6–2.8× longer than wide. Pronotum. Broad, 0.9× wider than long, strongly constricted anteriorly; discal surface with large punctures 3–5× the size of the abundant, minute punctures; interspaces narrower than diameter of small punctures, glossy; pronotal longitudinal midline indistinct; dorsal vestiture consisting of abundant cup-shaped setae and scattered thick bristles. Elytra. Length/width ratio 1.7–1.9 (avg. 1.8 ± 0.1); odd numbered interstriae raised, vestiture consisting of cup-shaped setae and erect thick bristles sparse on elevated interstriae. Declivity. As elytra but usually with shorter interstrial bristles. Ventral sclerites. Procoxae subcontiguous, precoxal region bluntly raised; margin of mesoventrite anteriorly extended and pointed ( Fig. 2 a); abdominal sclerites one and five longer than others, fifth more elongate in females than males. Legs. Third tarsal segment broader than second, fifth 2× broader at apex than at base. Aedeagus ( Fig. 6 , 7 ). Monotypic, see type species description.

Etymology: From the Greek “ pachy,” meaning thick and “ squamus,” meaning scale; for its distinct character of being thickly covered by scale-like setae in the shape of cups.

Type species: Hylastes subcostulatus Mannerheim 1853 , present designation.

Discussion. The genus Pachysquamus exhibits several exclusive characters that distinguish it from all other genera in the Hylastini . A character separating it from Hylurgops , and previously mentioned ( Chamberlin 1939, Swaine 1918, Wood 1982), is the raised, odd numbered elytral interstriae. The only other occurrence of raised interstriae in the Hylastini was described from the fossil of H. piger ( Wickham 1913) . This fossil questionably placed in the genus Hylurgops from a Miocene shale impression at Colorado’s Florissant Fossil Beds ( Fig. 8 ).

The dorsal vestiture of the pronotum of the monotypic P. subcostulatus consists of a dense cover of cup-shaped setae and a few sparse and erect bristles. In the remaining species in the Hylastini , the pronotal vestiture cover is either absent or consists of hair-like setae of varying lengths. As in the pronotum, the entire discal surface of the elytral in P. subcostulatus is covered by an abundant vestiture of recumbent, cup-shaped setae; in the other species of the Hylastini , this vestiture consists of recumbent to semi-erect hair-like setae. The interstrial vestiture of Pachysquamus and Scierus consists of sparse and erect thick bristles while it consists of thinner and usually recumbent hairs in all Hylurgops and some Hylastes species, or of a midline of short and arcuate, semi-recumbent hairs in most species of Hylastes .

As in Hylurgops and Hylastes , the female’s fifth ventrite of P. subcostulatus is longer than the combined length of ventrites three and four and is also longer than in males. Relative to Hylastes and Hylurgops , the aedeagus of P. subcostulatus is more elongate, 3.8× longer than wide compared with an average of 3.3× for Hylurgops examined (N =3 per species). Although Hylastes aedeagi were not measured, these were visibly stockier, with the apodemes proportionally shorter than their length, 0.59 vs. 0.70 for examined Hylurgops (N =3 per species) ( Figs. 6 a, 7a).

Due to the uniqueness of its elevated odd numbered interstriae ( Fig. 9 a), the cup-shaped setae dorsal vestiture ( Fig. 9 b), and the strongly pointed anterior margin of the mesoventrite ( Fig. 2 a), Hylurgops subcostulatus is distinct from the other species in the Hylastini and is assigned to a new genus. The subspecies previously treated by Wood (1982) are not recognized.

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 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 8. Hylurgops piger, drawing of a shale impression from Florissant, Colorado (modified from Wickham 1913).

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.