Oromia thoracica Machado & López, 2015

Machado, Antonio & López, Heriberto, 2015, A new species of Oromia (Coleoptera: Curculionidae) from the Canary Islands, Zootaxa 3931 (1), pp. 117-126 : 118-124

Oromia thoracica Machado & López n. sp.

( Figs. 1–3 )

Type series. Holotype 1 ♂, Canary Islands, Gran Canaria, Los Berrazales (480 m a.s.l., UTM 28R4355-31050), 30-XII-2013, H. López & E. Morales leg. ( DZUL 34166). Deposited in the entomological collection of the Department of Animal Biology (Zoology), University of La Laguna ( DZUL).

Paratypes: same data as holotype, 1♂, 1♀ (coll. H. López, La Laguna), 1 ♀ (coll. Machado, La Laguna); same locality as holotype, 1 ♀, 2-I-2009, H. López & E. Morales leg. (coll. Museo de Ciencias Naturales, Santa Cruz de Tenerife, TFMC, CO-16001); 1 ♀, same locality, 08-V-2014, H. López leg. (coll. P. Oromí, La Laguna).

Diagnostic features. Elongate, subparallel and depressed hypogean molytine of moderate size (3.7–5.0 mm, without head), eyeless and apterous (fig. 1a-c). Integument well sclerotized, dark reddish brown, almost glabrous, with tiny dispersed granules and covered by more or less developed foveae. Rostrum as long as pronotum, with several irregular micro-ridges along epifrons; scrobe sinuous, upper margin reaching base of rostrum, lower margin reaching ventral margin of rostrum at middle. Pronotum not constricted anteriorly, front margin broad and thick covering head (roof-like), laterally reflexed; with one wide submarginal depression on each side; front half with conspicuous median keel. Elytra with base concave and lateral angles sharply pointed, protruding; striae shallow, interstriae slightly rippled. Metapleurosternal sulcus absent; metaventral apophysis truncate, thickly bordered; first and second abdominal ventrite fused (suture obsolete), much longer than the rest together. Femora slender, unarmed; tibiae much compressed, uncinate; protibiae with premucro; tarsal plantae replaced by loose hairs; third tarsomere broad, bilobed; onychium long with free claws (fig. 3b).

Measurement of holotype (♂). Length: total 6.4 mm (with rostrum) 5.0 mm (without head); rostrum 1.35 mm; antenna 1.86 mm, scape 0.86 mm; funicle 0.56 mm, segments (1–4) 0.16/ 0.08/ 0.06 /0.06/ 0.05 /0.06 / 0.07 mm; club 0.44 mm; pronotum 1.40 mm (midline); elytra 3.45 mm; protibiae 1.40 mm, mesotibiae 1.14 mm, metatibiae 1.28 mm; metatarse 0.60 mm (segments 0.13/ 0.11 /0.17 / 0.24 mm); abdominal ventrites (1+2) 1.38, ventrites (3/4/ 5) 0.22/ 0.22/ 0.42 mm. Width: head 0.65 mm; rostrum 0.41 (at pterygia) 0.29 mm (at base) 0.34 mm (at middle); scape (base/apex) 0.02/ 0.10 mm; club 0.21 mm; pronotum (anterior/ maximum/ posterior) 0.84/1.28/ 0.92 mm; elytra 1.77 mm (maximum). Height: prorostrum 0.32 mm, metarostrum 0.28 mm; prothorax 1.02 mm, mesothorax 1.24 mm, abdomen 1.24 mm.

Description. Size moderate (s.r. 3.75–5.00 mm), body elongate, subparallel and depressed. Integument dull, of dark reddish-brown color (club lighter) and foveolate-rugose aspect; glabrous (except limbs), and with dispersed microgranules (tip of granules and ridges defined). Apterous.

Head completely covered by pronotum, eyeless. Rostrum narrow (L/W middle= 3.9–4.0), parallel, as long as pronotum, dorsally twice as wide as ventrally, slightly constricted at base and at level of antennal insertion (dorsally), widest at apex; epistome laterally separated from pregenae; pterygia short, moderately protruding; dorsum in lateral view straight at basal third, deflexed at middle and deflexed again at apical third; ventral margin moderately arcuate; dorso-lateral margins sharply keeled. Scrobes deep, not visible from above (except at pterygia); upper margin sinuous and reaching base of rostrum at mid-length; lower margin keeled, oblique, reaching ventral margin of rostrum at mid-length. Integument with several fine irregular micro-ridges along epifrons and foveae between the micro-ridges badly defined; ventral integument shinier, without ridges (only microgranules). Some short flat setae at prorostrum and distal part of metarostrum.

Antennae slender, inserted at ¾ of rostral length. Scape straight (0.7× length of rostrum), progressively but not much incrassate towards apex (slightly thickened at apex), integument smooth, with very few tiny setae. Funicle 7- segmented, compact (0.65× length of scape), desmomere 1 more than twice the length of 2; 3–6 subequal, slightly transverse; 7 thicker. Club large (L/W= 2.1), almost as long as funicle; rhaptomere 1 cup-shaped, longer than the rest together (fig. 3a).

Pronotum weakly convex, in dorsal view with outline elongate, somewhat rectangular (L/W= 1.1); apex strongly thickened, not constricted, margin reflexed (roof-like, covering head), slightly emarginate; lateral margins variable, little arcuate and convergent in apical third (anterior angles blunt, border thick, with asperities), subparallel in middle third, then straight and convergent basad (in one specimen somewhat undulate); base finely bordered, weakly emarginate; maximum width usually at apical third. Median line sharply keeled and conspicuous on apical half, flanked by shallow longitudinal depressions on disk, and by larger and deeper antero-lateral depressions; margins reflexed. Integument with large confluent foveae, intervals very narrow, forming an irregular sharp reticulate pattern (better defined in posterior half) or longitudinal irregular ridges on each side of disk. Microchaetae present.

Scutellum not visible.

Elytra elongate (L/W= 2.0), barely convex, subparallel, level with pronotum in lateral view, 2.5–2.6× longer and 1.4–1.5× wider than pronotum. Base concave, markedly keeled, slightly wider than base of pronotum; lateral angles acute, pointed, shortly protruding forwards; lateral margins subparallel, convergent at base, with separate granules (looking denticulate); maximum width and height at apical 4/5; apical declivity abrupt; apex uniformly rounded. Striae shallow, interstriae subconvex, somewhat rippled; with shallow diffuse foveae and sparse but conspicuous granules (tip shiny) in irregular rows. Microchaeta present, longer at apex.

Legs slender. Femora 1.3× length of tibiae, moderately inflated, thin at base, without teeth, with sharp-pointed internal subapical angle. Tibiae straight, strongly compressed, uncinate, with premucro; outer angle of protibia largely curved, fringed by tibial comb (long reddish setae); corbels with inner flanges as typical in Molytinae (figs. 4a,b,c). Tarsi broad, segment 2 transverse, segment 3 strongly bilobed, reaching half the length of onychium (fig. 3b); tarsal pads thin with loose long hairs. Integument foveolate-rugose with short setae; longer setae on inner face of tibiae and covering tarsi.

Ventral surface rather flat. Integument somewhat shinier than on dorsum. Prosternum with more or less impressed foveae (but almost effaced on antecoxal declivity), very deep and dense on metasternum, and more disperse and shallower on abdominal ventrites, vanishing towards the flanks and apex. Prosternum at apex depressed and constricted, foramen oblique (45º), retracted, occupying 0.60 of width. Procoxae very close, 1.5× its diameter distant from anterior margin and 0.5× from posterior margin. Mesoventrite punctate, mesoventral process flat, not protruding; mesocoxae separated by almost one diameter. Ventral margins of elytra submarginally deflexed along its length (integument smoother, only with granules). Metaventrite twice as broad as long, truncate at base, thickly bordered, at same level as abdominal ventrites; metanapleural sulcus not present; metacoxae little convex, separated by twice its diameter from each other, not reaching pleural margin. Abdominal ventrites 1+2 fused (suture not discernible), depressed at disk, 1.6× as long as rest of ventrites together, thickly bordered at base of intermetacoxal process, finely bordered at posterior margin; ventrites 3 and 4 subequal, very short, strongly depressed and thin at base, posterior margin incrassate, bordered; ventrite 5 as long as 3 and 4 together, broadly rounded (♀) or more truncate (♂) at apex, rugose, without special subterminal setae (only short inconspicuous microchaetae). Tergite 8 emarginate in females.

Aedeagus (fig. 2b, c). Pedon short and thick, with broad and asymmetric apex (acute in profile); temones 1.3× longer. Endophallus with two parallel broad, acute endosclerites, and several narrow, more apical ones. Tegmen with very short manubrium and broad translucent parameres ending with fringes. Spiculum gastrale robust, arcuate with strongly asymmetric arms (fig. 2d).

Female genitalia. Ovipositor short, styli strongly sclerotized, fused with the coxites, with a bunch of 8 radiating setae at apex (fig. 3d). Terguite VIII scoped out at posterior margin; terguie VII short (fig 3e). Spiculum ventrale with short manubrium and long divergent arms; plate broad with a large ovate fenestra at middle (fig. 3c). Spermatheca reniform, without lobes, ducts emerging at the base of the corpus (fig. 3e).

Biology and ecology. All individuals of this new species have been collected using MSS pitfall traps installed in a scoriaceous outcrop, poorly covered by a soil layer and with vegetation mainly characterized by Pinus canariensis , Euphorbia regis-jubae and several bushes characteristic of thermophilous habitats ( Cheirolophus arbutifolius , Pistacia atlantica , Pterocephalus lasiospermus , Artemisia thuscula , Withania aristata , Salvia canariensis ). The collection site is located in Los Berrazales, the upper section of the Agaete valley, in an older part of the island formed by Miocene volcanism, but the site itself is within younger terrain (represented by basanite scoria cones and lava flows) originated from a localized Holocene eruption. This part of the island was not directly affected by subsequent episodes of extensive volcanism that occurred in Gran Canaria during the Pliocene, of which one in particular, the formation of the Roque Nublo agglomerate complex, was very explosive and accompanied by extensive aerial emissions ( Pérez-Torrado et al. 1995). The upper part of the Agaete valley probably acted as a refuge for the biota of the humid areas destroyed by this explosive Pliocene volcanism, this being a possible explanation for the presence of some local endemic plants and animals. Most of the subterranean species collected in the MSS of Los Berrazales have not been found in other nearby sites located in more recent terrains. Thus, the role of the Agaete valley as a refuge may have been particularly important for subterranean habitats. Only two troglobitic species discovered in the MSS of Los Berrazales have also been found in other younger terrains: the millipede Dolichoiulus oromii Enghoff, 2012 and the spider Scotophaeus n. sp.

MSS pitfall traps from Los Berrazales have been continuously sampling since 2003, being revised every year after the dry and the rainy seasons. All individuals of O. thoracica were collected on three occasions, and with no clear seasonal pattern. However, the presence of a big, recently dead individual of Euphorbia regis-jubae very close to the traps may be the reason for the occurrence of O. thoracica in the traps, together with an increase in the richness and abundance of other species. Root putrescence of these bushes may attract and concentrate temporally the subterranean fauna of all trophic groups, and O. thoracica probably feeds on these decomposed roots, given that other Oromia species from Tenerife have been found around rotten roots inside caves. In comparison to the other Oromia species, O. thoracica has a more troglobitic appearance due to its more elongated and stylized legs and antennae. However, this new species must also be edaphobitic according to its habitat and supposed feeding habits.

Remarks. There are several aspects in which this new taxon differs from the already described Oromia species. The lower margin of the antennal scrobe (fig. 4d) reaches the venter of rostrum at the mid-point (not running parallel towards its base); the pronotum is not constricted anteriorly, but expanded over the head; the metanapleural sulcus is not present, like in Anchonidium Bedel, 1884 and Aparopion Hampe, 1861 ; in addition, the elytra are less sculptured, abdominal ventrites 1 and 2 are almost fused (suture not or hardly visible) and separated by a thick border from the metaventrite; the last abdominal ventrite does not have a pair of subapical setae, or these are extremely reduced. The median lobe of the male genitalia are of the same type, more asymmetric at the apex than in Oromia hephaestos Alonso-Zarazaga, 1987 (fig. 2c), but with strongly developed endosclerites instead of fields of small denticles. However, the spiculum ventrale and spermatheca of females (fig. 3c, e) are almost identical to those of O. hephaestos , and clearly different from those of Baezia or Styphloderes (Parastyphloderes) lindbergi . From this latter species, which has antennae with 5 instead of 7 desmomeres, it also differs by longer apical fringes in the blades of the proventriculus (fig. 3f), in contradiction with Israelson’s (1990) supposition.

We do not know the extent to which ventral structures respond in adaptation to endogean life, and O. thoracica could well represent a more endogean adapted form of Oromia . In any case, it seems more prudent to assign the new taxa to Oromia than separating it as a new genus. In order to clarify this question, a phylogenetic study including all species of the Molytinae in the Canary Islands is ongoing.

The most remarkable character of Oromia thoracica n. sp., and the reason for its specific epithet (an adjective), is the thickened and reflexed anterior margin of the pronotum, which covers and protects the head like a roof, thus lacking the characteristic lateral constriction which is the generalized case within the group.

Figures

FIGURE 1. Habitus of Oromia thoracica n. sp. (female). A: dorsal view. B: ventral view. C: lateral view.

FIGURE 2. Oromia thoracica n. sp. A: male ventrite VIII. B: aedeagus in lateral view. C: edeagus in dorsal view. D: spiculum gastrale with attached basal sclerites. E: female ventrite VII.

FIGURE 3. Oromia thoracica n. sp. A: antennal funicle and club. B: protarsus. C: spiculum ventrale. D: female gonostyli. E: spermatheca. F: lamina of proventriculus.