Pseudastenus Bernhauer, 1933

Busanello, Dilson G. C., Irmler, Ulrich & Caron, Edilson, 2020, Revision of Pseudastenus Bernhauer, synonym with Xenasterides Newton and six new species (Coleoptera, Staphylinidae, Paederinae), Zootaxa 4755 (1), pp. 139-154 : 140-141

Pseudastenus Bernhauer, 1933

Pseudastenus Bernhauer, 1933: 520 (original description); Bierig, 1939: 180 (mention the similarity with Xenaster Bierig ); Blackwelder, 1944: 127 (list of species); Blackwelder, 1952: 324 (nomenclatural notes); Bachmann et al., 2017: 14 (mention about type specimen in the MACN). Type species: Pseudastenus barretoi Bernhauer, 1933 (fixed by monotypy).

Xenaster Bierig, 1939: 179 (original description, preoccupied name, not Xenaster Simonwitsch, 1871 ); Blackwelder, 1944: 127 (list of species); Blackwelder, 1952: 405 (nomenclatural notes); Newton & Thayer, 1992: 62 (nomenclatural note); Navarrete-Heredia et al., 2002: 283 (nomenclatrual note, distribution); Bouchard et al., 2011: 221 (nomenclatural note); Asenjo et al., 2013: 280 (distribution). Type species: Xenaster plaumanni Bierig, 1939 (fixed by monotypy). New synonym.

Xenasterides Newton, 2017: 17 (replacement name for Xenaster Bierig, 1939 ). Type species: Xenaster plaumanni Bierig, 1939 (fixed by monotypy). New synonym.

Diagnosis. Pseudastenus differs from the other genera of Lathrobiini by having the following set of characters: head, pronotum and elytra with dense, microtuberculate, setiferous punctures; neck one-third as wide as head; antennae short, clavate, gradually widened from antennomeres 4 to 11; 11th antennomere equal in length to the three preceding antennomeres combined ( Fig. 2 ); anterior margin of labrum deeply emarginate at the middle, with four denticles, medial two denticles robust and each one with two spine-like setae, each external denticle with one spinelike seta ( Figs. 8 , 21 ); gula very narrow and parallel sided; pronotum trapezoidal, slightly wider than long, enlarged in anterior third ( Fig. 15 ); profurcasternum expanded caudally and laterally, almost contiguous with the pronotal hypomeron ( Fig. 16 ); profemur enlarged ( Fig. 27 ); protarsus not dilated; and metatibia with apical ctenidium on the posterior face.

Redescription. Male. Maximum body length 3.50 mm, humeral width 0.50 mm. Body elongate ( Figs. 36–37 , 40–45 ); head and pronotum equal in width, elytra conspicuously narrower and abdomen tapering to apex. Head, pronotum and elytra with dense, microtuberculate, setiferous punctures, surface matt ( Figs. 1 , 15, 18 ); abdominal segments slightly glossier. Abdominal setae longer than those of the remaining body, length of setae gradually increasing to the apex. Head: wider at base than at front, shape trapezoidal ( Fig. 1 ); basal margin with short medial emargination; neck one-third as wide as head. Antennae short, reaching the apical margin of pronotum; clavate, gradually widened from antennomeres 4 to 11; fine pubescence gradually increasing to apex; scape long, almost as long as four subsequent antennomeres combined; pedicel and antennomere 3 longer than wide, pedicel longer than 3rd; antennomere 4 subquadrate; antennomeres 5 to 10 wider than long; antennomere 11 almost two times longer than wide, length equal to the three preceding antennomeres combined ( Fig. 2 ); antennomeres 9 to 11 with glandular pores ( Figs. 3–7 ). Labrum transverse, with longitudinal median sulcus on the surface ( Fig. 8 , 21 ); anterior margin deeply emarginate at the middle, with four denticles, each medial two denticles robust and with two spinelike setae, each external denticles with one spine-like seta; lateral margin rounded. Mandibles symmetric, with three internal teeth, medial tooth shortest ( Figs. 9 , 22 ). Maxilla with short galea and lacinia, almost equal in length and densely ciliate ( Fig. 23 ); palpomere 1 longer than wide; palpomere 2 three times longer than wide, enlarged to apex; palpomere 3 longest, almost three times longer than wide, asymmetric with protuberant internal margin; palpomere 4 shortest, very small and acute ( Figs. 10, 11 , 23 ). Mentum hexagonal; wider than long ( Fig. 12 ). Labium with glossae subdivided in three dentate lobes, median lobe transverse and lateral lobes rounded ( Figs. 12, 13 ); Hypopharynx with lobes of spinelike setae on anterior margin ( Fig. 14 ). Labial palpomere 2 longest and six times longer 3 than palpomere 1, set of spine-like setae on the ventral margin of the internal face ( Figs. 12, 14, 17 ); 3 narrowest, parallel sides and truncate apex; palpomere 2 and 3 with internal face conspicuously concave ( Figs. 14, 17 ). Gula very narrow and parallel sides. Thorax: shape of pronotum trapezoidal ( Fig. 15 ); anterior margin curved; posterior margin slightly curved. Anterior and posterior angles with macrosetae, anterior setae longer than posterior setae. Pronotal hypomeron with conspicuous superior line deflected ventrally to the anterior margin; joining the prosternal transverse carina ( Fig. 16 ). Profurcasternum expanded caudally and laterally, almost contiguous with the pronotal hypomeron. Basisternum carinate and contiguous to the intercoxal carina ( Fig. 16 ). Posterior margin of elytra emarginate. Hind wings well developed or short and poorly developed. Mesoventrite long, with the same length of metaventrite ( Fig. 19 ); mesocoxae contiguous; mesoventrite process longer and sharper than metaventrite process. Tarsal formula 5-5-5; tarsomere 1 longest and 4 shortest ( Fig. 27 ). Profemur enlarged ( Fig. 27 ); metatibia with apical ctenidium on the posterior face. Abdomen: segments III–V parallel sided, VI–VIII tapering to abdominal apex. Segments III–VI with two pairs of paratergites, narrow and equally long as tergites ( Figs. 24–25 ); segments VII–VIII without pair of paratergites, but with lateral lobes ( Fig. 26 ). Tergite VIII with posterior margin pointed at the middle ( Fig. 28 ); sternite VIII with posterior margin broadly rounded ( Fig. 29 ). Tergite IX with long and symmetrical ventral struts ( Fig. 30 ), anterior and posterior margin conspicuously emarginate at the middle; sternite IX three times longer than wide ( Fig. 31 ), posterior margin rounded and median three-fifths fringed and pair of subapical macrosetae. Tergite X trapezoidal, anterior margin curved; latero-apical and posterior margin fringed, with two or three subapical macrosetae ( Fig. 32 ). Aedeagus elongate, 3.7 to 5.9 times longer than wide; parameres not distinguishable; median lobe with two pairs of internal sclerites, the basal pair more robust than apical; and ejaculatory duct with two trifurcate sclerites (at least in P. plaumanni and P. ribeirocostae ) ( Figs. 46, 47 ).

Female. Similar to male, except for tergite IX without ventral struts, almost totally divided longitudinally ( Fig. 33 ); hemisternite IX with set of subapical macrosetae and posterior margin fringed ( Fig. 34 ); tergite X similar to male, but with 4 anterior margin pointed ( Fig. 35 ). Sclerotized spermatheca not found. The females should be identified by association with the male.

Geographical records. Mexico (Quintana Roo) , Colombia (Risaralda) , Peru (Huánuco) , Brazil (Amazonas, Distrito Federal, Goiás, Rio de Janeiro, Paraná, Santa Catarina) ; Argentina (Chaco, Jujuy, Missiones ) .

Remarks. The species of the genus are usually rare and found in restricted areas. They were usually collected in only small numbers at their sampling locations. Only P. plaumanni seems to have a wider distribution from southeastern Peru to northern Argentina. According to information given by Lee Herman (AMNH), a higher number of species can be expected regarding the material deposited already in museums waiting to be described which can be also derived from species only present as female specimens for this study. As the information labelled to the studied specimens, the species of the genus live in the litter layer of rainforests. As two species groups could be differentiated one with normally developed elytra and hind wings and one with reduced elytra of hind wings, two groups with different ecologically demands can be separated. The first group with well-developed elytra certainly life in the upper humus layer of the forests, whereas the second group with reduced hind wings will prefer deeper humus horizons. Furthermore, the reduced flight ability indicates a low distribution ability and, thus, a more restricted distribution than in the group with well-developed hind wings. They may represent relict species which indicate former relict forest patches during ice age more even earlier geological eras. In particular more species of this group can be expected in mountainous regions such as in the Atlantic forest in Brazil or the eastern slope of the Andean range.

Figures

FIGURES 1–11. Scanning Electron Microscopy of Pseudastenus plaumanni. 1. Head, dorsal view; 2. Antenna; 3.Antennomere 9; 4. Glandular pore, antennomere 10; 5. Antennomere 10; 6. Glandular pore, antennomere 9; 7. Antennomere 11, arrow indicates glandular pores; 8. Labrum, dorsal view; 9. Mandible, dorsal view; 10. Maxillary palpus, ventral view; 11. Maxillary palpomere 4.

FIGURES 21–29. Pseudastenus plaumanni. 21. Labrum, dorsal view; 22. Mandibles, dorsal view; 23. Maxilla, ventral view; 24. Tergites I–III, dorsal view; 25. Tergite VI, dorsal view; 26. Tergite VII, lateral view; 27. Foreleg, external view; 28. Tergite VIII, dorsal view; 29. Sternite VIII, dorsal view. Scale bars: 0.2 mm.

FIGURES 12–20. Scanning Electron Microscopy of Pseudastenus plaumanni. 12. Labium, ventral view; 13. Detail of glossa, lateral lobe, ventral view; 14. Labium, dorsal view; 15. Pronotum, dorsal view; 16. Pronotum, ventral view; 17. Detail of labial palpomere 3, dorsal view; 18. Elytron, dorsal view; 19. Meso and metaventrite, ventral view; 20. Abdominal sternites I–III.

FIGURES 36–39. 36. Pseudastenus barretoi, lectotype, dorsal view (FMNH); 37. P. plaumanni, lectotype, dorsal view (FMNH); 38. Labels from the lectotype of P. barretoi (FMNH); 39. Labels from the lectotype of P. plaumanni (FMNH). Scale bars: 2 mm.

FIGURES 40–45. Dorsal view. 40. Pseudastenus ribeirocostae sp. nov.; 41. P. ferrugineus sp. nov.; 42. P. latus sp. nov.; 43. P. oculatus sp. nov.; 44. P. amazonicus sp. nov.; 45. P. schubarti sp. nov. Scale bars: 2 mm.

FIGURES 30–35. Pseudastenus plaumanni. 30. Tergite IX, male, dorsal view; 31. Sternite IX, male, ventral view; 32. Tergite X, male, dorsal view; 33. Tergite IX, female, dorsal view; 34. Hemisternite IX, female, ventral view; 35. Tergite X, female, dorsal view. Scale bars: 0.2 mm.

FIGURES 46–47. Aedeagus of Pseudastenus plaumanni. 46. Dissected from the lectotype (FMNH), dorsal view. 47. Dissected from a specimen collected in the type locality, dorsal and lateral view, respectively. Details: a, basal sclerite; b, apical sclerite; c, basal sclerite of the ejaculatory duct; d, apical sclerite of the ejaculatory duct. Scale bars: 0.2mm.