Brasixenos Kogan & Oliveira, 1966, stat. res.

Benda, Daniel, Pohl, Hans, Nakase, Yuta, Beutel, Rolf & Straka, Jakub, 2022, A generic classification of Xenidae (Strepsiptera) based on the morphology of the female cephalothorax and male cephalotheca with a preliminary checklist of species, ZooKeys 1093, pp. 1-134 : 1

Brasixenos Kogan & Oliveira, 1966, stat. res.

Brasixenos Kogan & Oliveira, 1966: 358. Type species: Brasixenos fluminensis Kogan & Oliveria, 1966, by original designation.

Xenos Rossi, 1793 (partim!) (synonymy proposed by Kinzelbach 1971b: 160).

Brasixenos Kogan & Oliveira, 1966 (restored from synonymy by Trois 1988: 268).

Xenos Rossi, 1793 (partim!) (synonymy proposed by Cook 2019: 232).

Diagnosis of female cephalothorax.

Maxilla distinctly reduced, flattened, anteriorly rounded, not distinctly prominent; fused to labial area but well defined by its strong sclerotization, conspicuous compared to usually pale cephalothorax as in Nipponoxenos and some species of Xenos . Maxillary bases appear connected and fused to each other. Vestigial palps differ from those of all other genera, preserved only as inconspicuous concavity on wrinkled maxillary surface, without any vestigial plate. Located anteriorly on ventral side of maxilla, at level of mandibles (Fig. 22E ). Clypeal area not delimited from labral area, apparently more or less fused (Fig. 22D ). Mandible nested in capsule. In contrast to Paragioxenos , head and prothorax ventrally delimited by birth opening medially and by suture laterally.

Description of female cephalothorax.

Shape and coloration. Compact and usually ovoid, ca. as long as wide, or slightly wider, rarely longer than wide. Abdominal segment I of some species extruded laterally, forming corner below abdominal spiracles. Species relatively variable in size, length 0.76-1.62 mm, maximum width 0.72-1.74 mm. Anterior head margin evenly rounded or protruding. Thorax slightly to strongly widening posteriorly, sometimes subparallel. Coloration mostly pale, with light shadows of brown dominating. Some parts of cephalothorax, especially maxillae, dark and sclerotized.

Head capsule. Including lateral extensions ~ ⅓- ½ as long as entire cephalothorax. Color pattern formed by shades of pale and dark brown, with maxillae always dark. Clypeal area not delimited from labral area, apparently more or less fused, slightly or distinctly protruding anteriorly, always forming clypeal lobe (Fig. 22D ). Surface wrinkled apically on clypeal lobe (sometimes with lamellar structures), smooth ventrolaterally and dorsally. Clypeal surface with ~ 50-70 sensilla or more. Border between clypeal and frontal region indistinguishable. Frontal area smooth. Segmental border between head and prothorax difficult to recognize on dorsal side in some specimens.

Supra-antennal sensillary field. Smooth or slightly wrinkled, with dispersed sensilla. Not delimited or indistinctly by furrow on medial side.

Antenna. Preserved only as elongated depression or inconspicuous furrow (Fig. 21C ). Rounded plate, small cavity or sensilla missing. Periantennal area slightly wrinkled or smooth.

Labrum. Ventral field slightly wider than long, nearly circular. Dorsal field anterior to mouth opening slightly arcuate, at least 4 × wider than long at midline, with setae inserted in cavities on surface.

Mandible. Anteriorly to anteromedially directed at angle of 40-70°, enclosed in capsule. Mandibular bulge sometimes indistinct, with up to ten spine-shaped or blunt sensilla, or lacking these structures. Cuticle completely sculptured or partially smooth. Tooth narrow, armed with several rows of spines.

Maxilla. Reduced and not protruding, fused to labium but clearly indentifiable by distinct sclerotization; appearing connected and fused medially, with sclerotization continuous along birth opening. Cuticle distinctly wrinkled. Apical maxillary region almost reaching upper edge of mandible in some species. Vestige of palp present as inconspicuous cavity on wrinkled maxillary surface, lacking vestigial plate. Located anteriorly on ventral side, at level of mandibles. Maxillary base slightly raised and less sclerotized than anterior region (Fig. 20C ). Submaxillary groove slightly produced posterolaterally.

Labium. Labial area recognizable between maxillae but fused with them, anteriorly delimited by mouth opening; convex, wider than long in midline, pale laterally, strongly sclerotized medially and around mouth opening. Cuticular surface smooth or wrinkled, with wrinkles indistinct on well sclerotized areas.

Mouth opening. Arcuate to distinctly U-shaped, sclerotized around margin.

Thorax and abdominal segment I. Pro-mesothoracic and meso-metathoracic borders more or less distinct, usually indicated by pigmented stripes or changed coloration on dorsal side. Mesal furrows absent. Border between metathorax and abdomen usually indicated by change in coloration or cuticular sculpture, separating ridge indistinct. Cuticle of thoracic segments with smooth surface on the ventral side, in some cases with small scattered pigmented papillae. Dorsal side of thorax usually completely smooth. Prosternal extension not very distinctly prolonged, usually evenly arched. Thoracic segments constricted laterally, distance between lateral extensions of head and spiracles thus reduced (Fig. 20D ). Setae and cuticular spines present on lateral region of abdominal segment I (Fig. 21E ).

Spiracles. Spiracles situated on posterior half or posterior third of cephalothorax, slightly elevated, with anterolateral orientation.

Diagnosis of male cephalotheca.

Differing from other genera by fusion of maxilla with cephalotheca. Maxillary cuticular surface with longitudinal grooves (Fig. 23E ). Vestige of maxillary palp visible (distinct in optical microscope, very inconspicuous on SEM micrographs) (Fig. 23A, D ).

Description of male cephalotheca.

Shape and coloration. Laterally rounded in frontal view, elliptic, in lateral view pointed anteriorly. Coloration mostly dark, but with some lighter areas such as ocular region or surroundings of maxillary palps (Fig. 23A ).

Cephalothecal capsule. Compound eyes with darker individual ommatidia well visible on pale ocular background. Clypeus with longitudinal pale line (Fig. 23A ). Clypeal lobe arcuate or straight in frontal view, prominent in lateral view; with sensilla evenly dispersed. Frontal region with conspicuous impression (Fig. 23D ). Diameter of genae between maxillary base and compound eye large,> 2 × as large as diameter of vestigial antenna. Occipital bulge absent.

Supra-antennal sensillary field. Kidney-shaped and bulging, medially delimited by frontal impression, with visible but indistinct furrows.

Antenna. Of standard shape, small, with complete torulus. Periantennal area indistinct but present. Sensilla usually absent.

Labrum. Labral area well visible but dorsal field not clearly separated from clypeus. Setae on dorsal field present.

Mandible. Anteromedially directed, pale centrally and dark laterally. Mandibular bulge not conspicuous, with several sensilla.

Maxilla. Not recognizable as separate structure, fused with cephalotheca. Cuticular surface of maxillary area sculptured, with longitudinal grooves (Fig. 23E ). Vestige of palp well visible (with light microscope, very indistinct on SEM micrographs) (Fig. 23A, D ).

Labium and hypopharynx. Distinct, inserted between and below maxillae, completely dark. Praementum and postmentum very indistinctly separated. Hypopharyngeal protuberance recognizable, not well delimited.

Mouth opening. Well visible, U-shaped, partially covered by ventral labral field.

Phylogenetic relationships.

Sister to a large clade containing representatives of genera previously known as Pseudoxenos , Paraxenos , and Xenos ( Benda et al. 2019).

Diversity and distribution.

Group of Xenidae with origin in the New World and restricted to this region. Comprising seven species, all of which are known from Brazil.

Hosts.

Various genera of Epiponini ( Vespidae : Polistinae ).

Comments.

The genus Brasixenos was described and differentiated from Xenos by Kogan and Oliveira (1966), but the description of the female cephalothorax was superficial. Although Kinzelbach (1971b) treated Brasixenos as a junior synonym of Xenos , Trois (1988) attempted to reinstate Brasixenos as a valid genus. Nevertheless, no author has followed this opinion ( Cook 2019). Although Kogan and Oliveira (1966) expected a close relationship of Xenos with Brasixenos in their description, Benda et al. (2019) revealed the group as a separate lineage unrelated to Xenos . We classify Brasixenos as a valid genus, based on a molecular phylogeny ( Benda et al. 2019, 2021) and morphological characters newly reported here.

Figures

Figure 20. Brasixenos araujoi (Oliveira & Kogan), host, female, cephalothorax, photomicrographs A Apoica pallens (Fabricius) stylopized by female of B. araujoi, lateral view B detail of host abdomen with adult female inside C ventral side of cephalothorax D dorsal side of cephalothorax. Abbreviations: mx - vestige of maxilla, mxb - maxillary base.

Figure 21. Brasixenos araujoi (Oliveira & Kogan), female, cephalothorax, SEM micrographs A ventral side B dorsal side C left vestigial antenna, dorsal side D right vestigial antenna, dorsal side E left lateral border of abdominal segment I below spiracle, dorsal side F detail of anterior border of cephalothorax, dorsal side. Abbreviation: a - vestigial antenna.

Figure 22. Brasixenos araujoi (Oliveira & Kogan), female, cephalothorax, SEM micrographs A anterior part of cephalothorax, ventral side B anterior part of cephalothorax, dorsal side C mouthparts, ventral side D detail of anterior border of cephalothorax, ventral side E right mandible and maxilla, ventral side F left mandible and maxilla, ventral side. Abbreviation: mxp - vestige of maxillary palp.

Figure 23. Brasixenos sp., male, cephalotheca, photomicrographs, SEM micrographs A frontal view B lateral view C vestigial antenna D frontal view E mouthparts. Abbreviations: cl - clypeus, fi - frontal impression, mx - vestige of maxilla, mxp - vestige of maxillary palp.