Scapomegas Lacordaire, 1854

Leivas, Fernando W. T., Bicho, Carla L., Degallier, Nicolas & Moura, Daniel P., 2012, Revision of the genus Scapomegas Lacordaire, 1854 (Coleoptera: Histeridae: Omalodini), Zootaxa 3482, pp. 33-46 : 34-41

Scapomegas Lacordaire, 1854

Scapomegas Lacordaire, 1854: 265 (valid description of the genus); Marseul, 1855: 129 –133, 494 (detailed description of the genus and new species); Gemminger & Harold, 1868: 779 (catalogue); Lewis, 1905: 50 (catalogue); Bickhardt, 1910: 70 (catalogue); 1917: 231–232 (morphological characters/geographical distribution/designation of the type species of the genus); Blackwelder, 1944: 186 (catalogue); Mazur, 1984: 298 (catalogue); Helava et al., 1985: 130 (citation); Mazur, 1989: 37 (key to genera of the tribe); Mazur, 1997: 90 (catalogue); Kovarik & Caterino, 2005: 193 (catalogue); Bicho & Degallier, 2008 (preliminary revision); Leivas, 2009: 31 –35 (taxonomic study); Mazur, 2010: 142 (new record of distribution); Degallier et al., 2011: 44, 46–47 (citation); Mazur, 2011: 75 (catalogue).

Type species: Scapomegas auritus Marseul, 1855 (subsequent designation by Bickhardt, 1917: 232).

Diagnosis. Body oval and strongly convex; rudimentary supraorbital stria indicated posteriorly; frontal and occipital striae absent; base of antennal scapus abruptly expanded and approximately parallel-sided from there to apex, last segments of the funicle projected and with bristles inserted on the lower surface; marginal pronotal stria interrupted behind the head; prosternum slightly emarginated posteriorly; mesosternum with a weak median projection at the anterior margin; anterior, middle and hind tibiae with a row of spines on outer margin and the submarginal region; 8th sternite in ventral view with bristles on lateral-posterior region; aedeagus with apical region of the parameres thin and “forceps”-shaped.

Redescription. Length (pronotum+elytra): 3.40–4.83 mm; elytral width: 3.12–4.24 mm.

Body oval and strongly convex; sutural region of the elytra slightly impressed or flat; usually dark or darkbrown, sometimes metallic blue; shining ( Figs. 1–2 ).

Frontal and occipital striae absent, supraorbital stria rudimentary and indicated posteriorly; frontoclypeal suture absent. Labrum convex and rounded anteriorly ( Fig. 3 A). Gena with a fovea in each side of lateral-posterior region ( Fig. 4 A). Left mandible longer than the right one ( Fig. 4 B). Mentum subquadrate and with a shallow emargination at the apex; prementum long; basal segment of labial palpi short, second subrectangular with micro-setae, third segment elongated with micro-setae ( Fig. 4 C). Maxilla with lacinial hook ( Fig. 4 D). Base of antennal scapus abruptly expanded, approximately parallel-sided from there to apex, somewhat sinuate along outer margin ( Fig. 3 A); last segments of the funicle projected and with bristles in the lower surface; antennal club oval, pseudo-sutures inwardly arcuate ( Fig. 3 C).

Pronotum with marginal stria interrupted behind the head and descending to the lower outer edge at least in posterior half; lateral stria abbreviated basally to complete ( Fig. 5 ). Prosternum with stronger punctuation on the sides, slightly emarginated posteriorly; prosternal keel with the carinal stria converging anteriorly and with a pair of orifices on the anterior region and other near the coxal cavity; prosternal lobe rounded and with the marginal stria complete ( Fig. 3 B); antennal club cavity with microstriae.

Elytra with a prominent humeral callus; marginal stria complete; strong dorsal striae, 1st stria complete, 2nd and 3rd striae variable, 4th and 5th striae indicated apically, sutural stria present; posterior region depressed on the first three dorsal striae ( Fig. 1 A, C, E). Mesosternum short, less than half the length of the prosternal keel ( Fig. 1 B, D, F); with a weak median projection at the anterior margin; marginal mesosternal stria interrupted or not at the middle ( Fig. 1 B, D, F). Metasternum with lateral stria complete or not and curved outward to metasternalmesepimeral suture; postmesocoxal stria usually present.

Outer margin of the anterior femur with strong punctuation and apical edge with a carina bearing bristles. Anterior tibiae wider at the middle; outer margin with small teeth bearing spines, outer submarginal region with a row of weak spines and a complete stria under it; with a row of weak spines on the inner marginal stria ( Fig. 4 E); anterior face with a row of weak spines at the middle following the tarsal cavity, the cavity itself straight. Outer margin of middle and hind tibiae with small teeth bearing spines and submarginal region with a row of spines; inner margin with spines and marginal stria complete ( Fig. 4 F, G).

First visible abdominal sternite with stronger punctuation laterally and with first visible abdominal sternite stria present only laterally ( Fig. 1 B, D, F); 4th visible abdominal sternite with an orifice on each side.

Male terminalia. Eighth tergite truncated or feebly emarginated on posterior margin; 8th sternite with bristles on the lateral-posterior region ( Fig. 6 A–C); 9th sternite emarginated posteriorly ( Fig. 6 D–F); 10th tergite feebly sclerotized, visible or not. Aedeagus with apical region of the parameres thin and “forceps”-shaped ( Fig. 7 ), ventrally at the apex with micro-setae on a small area. Apex of median lobe exposed.

Female terminalia. Coxites at least twice as long as wide, with a subapical lateral projection next to the cavity for insertion of stylus ( Fig. 8 A–C). Spermatheca globose, without constraining rings. Accessory spermathecal gland duct inserted under the spermatheca; accessory spermathecal gland membranous and elongated, larger than the spermatheca ( Fig. 8 D–E).

Remarks. Although both descriptions by Marseul (1855, 1887) are detailed, the author made errors when describing some characters: in 1855 he characterized the genus by the antennal club being composed of four segments and marginal pronotal stria present only at the anterior angles of the pronotum. In fact the clubs of the antennae are composed by three segments and the marginal pronotal stria is present along the lower outer edge at least in the posterior half of the pronotum.

The orifices recognized on the prosternal keel, lateral margin of the pronotum and elytra, and 4th visible abdominal sternite of Scapomegas are widely found in Histerinae and already mentioned by Leivas (2009). Some Omalodes Dejean, 1833 when captured release a noxious smelling liquid through orifices of the prosternum, which can be associated with defense glands. The second series of spines of the tibiae can be represented at the median region of the tibiae.

The following characters mentioned by Degallier et al. (2011) make this genus a singular group among the known Neotropical Omalodini : prosternum weakly emarginated posteriorly (rounded/acuminated in Omalodes Dejean and Ebonius Lewis, 1885 , and truncated in Sphyracus Marseul, 1853 ); anterior margin of mesosternum with a slight projection on the middle (emarginated in Omalodes and Ebonius and truncated in Sphyracus ); and the pattern of the spines present at the anterior tibiae (just a row of spines on the outer margin in Omalodes , Ebonius and Sphyracus Marseul, 1853 ).

The body shape, the base of antennal scapus abruptly expanded and approximately parallel-sided from there to apex, the prosternal keel and 9th sternite shape are some characters shared by Scapomegas and Asolenus Lewis, 1906 . The posterior region depressed on the first three dorsal striae is also found in Asolenus and Notolister Lewis, 1894 , and all these characters differentiate Scapomegas from Lewisister Bickhardt, 1912 and Atribalus Bickhardt, 1921 . In this sense we can note that Scapomegas share more similarities with Afrotropical Omalodini than Neotropical and Oriental genera of Omalodini .

Distribution. The known distribution is restricted to South America: Ecuador (Orelhana), Venezuela (Amazonas and Bolívar), French Guiana, Suriname, Bolivia (Santa Cruz), Peru (Huanuco), Brazil (Amazonas, Pará, Minas Gerais, Rio de Janeiro, Espírito Santo, São Paulo and Paraná), Paraguay (Concepcion, Canendiyú, Alto Paraná and Caazapa) and Argentina (Misiones). Scapomegas is herein registered for the first time in Argentina ( S. aurifer and S. gibbus ), Paraguay ( S. aurifer ), Ecuador and Peru ( S. auritus ) ( Fig. 9 ).

Apparently there is a relation between the pattern of distribution for the species and the vegetation from each region. Scapomegas aurifer and S. gibbus are related to the Atlantic Forest biome and are sympatric in the Seasonal Semideciduous Tropical (in the northern region of Paraná State). Scapomegas auritus is restricted to the Amazon biome. However, we emphasize the lack of samplings made to capture histerid beetles in the Brazilian biomes of Caatinga, Pantanal and Pampa.

Ecological data. Known from elevations of 0–1600 meters. The species of Scapomegas can be collected utilizing pitfall and flight interception traps (FIT) and the efficiency of those traps being greater when bait are

Figures

FIGURE 1. Dorsal and ventral habitus. A – B. Scapomegas auritus Marseul; C – D. Scapomegas gibbus Marseul; E – F. Scapomegas aurifer Marseul. Scale 1 mm.

FIGURE 2. Lateral habitus. A. Scapomegas auritus Marseul; B. Scapomegas gibbus Marseul; C. Scapomegas aurifer Marseul. Scale 1 mm.

FIGURE 3. Scapomegas auritus Marseul. A. Head in frontal view; B. Prothorax in ventral view; C. Detail of the last antennal segments of the funicle and antennal club. D. Propygidium and pygidium in posterior view.

FIGURE 4. Scapomegas auritus Marseul. A. Head, ventral view; B. Mandibles, dorsal view; C. Labium; D. Maxilla; E. Anterior leg; F. Middle leg; G. Hind leg.

FIGURE 5. Pronotum. A. Scapomegas auritus Marseul; B. Scapomegas gibbus Marseul; C. Scapomegas aurifer Marseul. Scale 1 mm.

FIGURE 6. Eighth sternite of the male terminalia with detail of the bristles on the sides of the posterior margin (A – C, scale 0.5 mm and 0.125 mm, respectively) and ninth sternite and tergite (D – F, scale 0.5 mm). A, D. Scapomegas auritus Marseul; B, E. Scapomegas gibbus Marseul; C, F. Scapomegas aurifer Marseul.

FIGURE 7. Aedeagus in ventral and dorsal view, respectively. A. Scapomegas auritus Marseul; B. Scapomegas gibbus Marseul; C. Scapomegas aurifer Marseul. Scale 0.5 mm.

FIGURE 8. Scapomegas auritus Marseul. A. Coxites in dorsal view, scale 1 mm; B. Coxites in lateral view, scale 1 mm; C. Detail of the coxites in ventral view, scale 0.25 mm; D. Bursa copulatrix, spermatheca and accessory spermathecal gland, scale 1 mm; E. Detail of the spermatheca and accessory spermathecal gland. Scale 0.25 mm.

FIGURE 9. Known distribution of Scapomegas Lacordaire in South America.