Paraxenos Saunders, 1872

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

Paraxenos Saunders, 1872

Paraxenos Saunders, 1872: 45. Type species: Paraxenos erberi Saunders, 1872, subsequent designation by Pierce (1908).

Paraxenos (Bembicixenos) ( Székessy, 1955: 280) (considered as subgenus by Kinzelbach 1971b: 162).

Bembicixenos Székessy, 1955: 280 (synonymized by Kinzelbach 1978: 82). Type species: Pseudoxenos (Bembicixenos) hungaricus Székessy, 1955, by original designation.

Diagnosis of female cephalothorax.

Differing from Tachytixenos by a narrower mandibular tooth and a differentiated prosternal extension. Prosternum with anterior swelling (Fig. 18A ) similar to Paragioxenos , or with distinct color pattern. Clypeal sensilla well visible, extending to ventral side of clypeal area. Vestige of antenna preserved as cavity (Fig. 17D ), additional rounded plates rarely present. Maxillae of two types, fused with labial area or distinctly separated and prominent as in Tachytixenos , Pseudoxenos , and Tuberoxenos . 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, very variable in shape, distinctly longer than wide, or wider than long. Size very variable, length 0.94-1.9 mm, maximum width 0.8-2.57 mm. Anterior head margin distinctly protruding. Thorax slightly widening posteriorly, sometimes subparallel. Coloration varying from light to dark brown. Cephalothorax displaying multiple brown shades forming distinct patterns (Fig. 16C, D ).

Head capsule. Ca. ⅓- ½ as long as entire cephalothorax including lateral extensions. Coloration pale to dark, always with species specific patterns. Clypeal area not delimited or well separated from labral area, protruding anteriorly, always forming clypeal lobe. Surface smooth or very slightly wrinkled. Very distinct sensilla mainly concentrated on clypeal lobe and extending to ventral side of clypeal area. Border between clypeal and frontal region usually not clearly recognizable but present, rarely more distinct. Frontal region distinctly wrinkled or covered by papillae. Segmental border between head and prothorax very indistinct on dorsal side, in most specimens virtually unrecognizable.

Supra-antennal sensillary field. Smooth or slightly wrinkled, with dispersed sensilla, delimited by distinct furrow on medial side (Fig. 18B ).

Antenna. Preserved as cavity (Fig. 17D ), rarely combined with rounded plates. Antennal sensilla or vestigial setae missing. Periantennal area smooth, sometimes reduced when supra-antennal sensillary field almost reaches vestige of antennae.

Labrum. Ventral field distinctly wider than long, elliptical or semicircular. Dorsal field arcuate to nearly straight,> 3 × wider than long in midline. Dorsal field with ~ 20-25 setae inserted in cavities.

Mandible. Anteromedially directed at an angle of 30-65°, enclosed in mandibular capsule or rarely protruding from it. Mandibular bulge not distinctly raised, with ~ 5-18 sensilla. Cuticle completely smooth, or partially sculptured on articulatory area. Mandibular tooth narrow or slightly widened, pointed or blunt, armed with distinct spines.

Maxilla. Very variable, well-developed and separated from labial area, or fused with it and strongly reduced. Cuticle always smooth. Prominent, anteriorly or anteromedially directed, in some cases partially overlapping with mandible proximally. Distal maxillary region not projecting beyond mandible anteriorly. Vestige of palp distinct, forming cavity or small bulge with more or less distinct plate. Located anteriorly or medially on ventral side of maxilla. Submaxillary groove distinctly produced posterolaterally (Fig. 18A ).

Labium. Labial area between maxillae distinct, delimited anteriorly by mouth opening and posteriorly by birth opening. Wider than long in midline and flat. Cuticular surface smooth or slightly reticulated.

Mouth opening. Distinctly arcuate to straight, sclerotized around margin.

Thorax and abdominal segment I. Pro-mesothoracic and meso-metathoracic borders more or less distinct, usually separated by mesal furrows on ventral side, rarely combined with pigmented stripes or spots on dorsal side, but not recognizable dorsally in most specimens. Border between metathorax and abdomen usually formed by ridge. Cuticle of thoracic segments reticulate on ventral side, often with small, scattered pigmented papillae. Dorsal side of thorax smooth or slightly reticulated. Prosternal extension anteriorly with arcuate to semicircular swelling in most species, or lacking swelling but with distinct color pattern. Meso- and metathorax unmodified in shape, transverse. Setae and cuticular spines present on lateral region of abdominal segment I (Fig. 17E ).

Spiracles. On posterior third of cephalothorax, slightly elevated, with anterolateral or anterodorsal orientation.

Diagnosis of male cephalotheca.

Characterized by distinct and relatively wide furrow of supra-antennal sensillary field (Fig. 19A, D ). Differing from sister genus Tachytixenos in shape of the mandibular tooth, which is conspicuously pointed and not in contact with mandibular bulge. Diameter of genae between maxillary base and compound eye 2 × or several times larger than diameter of vestigial antenna. Cephalotheca of elliptic shape in frontal view.

Description of male cephalotheca.

Shape and coloration. Elliptic and rounded laterally in frontal view, also almost rounded in lateral view. Coloration forming pattern of pale and dark shades.

Cephalothecal capsule. Compound eyes with darker individual ommatidia well visible on pale background. Clypeal lobe straight in frontal view, not prominent in lateral view. Sensilla dispersed on clypeal surface. Frontal region with paired furrow of supra-antennal sensillary field, lacking impression or occipital bulge. Diameter of genae between maxillary base and compound eye very large,> 3 × as large as diameter of vestigial antenna.

Supra-antennal sensillary field. Kidney-shaped and bulging, delimited medially by distinct furrow. Furrows relatively wide, not connected anteriorly (Fig. 19A, D ).

Antenna. Of standard shape, small, with small plates and cavity (Fig. 19C ), torulus interrupted. Periantennal area not clearly delimited from supra-antennal sensillary field.

Labrum. Labral area distinct. Setae present on dorsal field.

Mandible. Anteromedially directed. Tooth apically pointed, not very wide basally, not reaching area of mandibular bulge (Fig. 19E ), which bears sensilla.

Maxilla. Distinct, prominent. Coloration pale centrally and dark laterally. Vestige of palp distinct, dark.

Labium and hypopharynx. Labium distinct between and below maxillae, dark. Praementum and postmentum indistinctly separated by furrow. Hypopharyngeal protuberance present or not.

Mouth opening. Well visible, not covered by ventral labral field, slightly arcuate.

Phylogenetic relationships.

Forming a clade of Palearctic origin with Tachytixenos ( Benda et al. 2019).

Diversity and distribution.

Thirteen described species, distributed in the Old World and Australia.

Hosts.

Bembecinus , Bembix and Stizus spp. ( Bembicidae : Bembicinae ).

Comments.

Paraxenos was described by Saunders (1872) but only a superficial description of the male was provided. Kinzelbach (1971b) synonymized several additional genera with Paraxenos , all of them described by Pierce (1908, 1909, 1911, 1919) from the New World ( Eupathocera , Opthalmochlus , Homilops , Sceliphronechthrus ) and Old World ( Tachytixenos ). He also classified Bembicixenos described by Székessy (1955) as subgenus of Paraxenos , but later considered it a synonym of Paraxenos ( Kinzelbach 1978). We classify Paraxenos as a valid genus based on monophyly revealed by a molecular phylogeny ( Benda et al. 2019, 2021) and based on morphological characters newly reported here.

Figures

Figure 16. Paraxenos erberi Saunders, host, male, female, cephalothorax, photomicrographs A Bembecinus peregrinus (Smith) stylopized by P. erberi, lateral view B detail of host abdomen with female under third tergite and male puparium under fourth tergite C ventral side of female cephalothorax D dorsal side of female cephalothorax.

Figure 17. Paraxenos sp., 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 18. Paraxenos sp., 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. Abbreviations: fssf - furrow of supra-antennal sensillary field, ps - prosternal swelling, sbhp - segmental border between head and prothorax, smxg - submaxillary groove.

Figure 19. Paraxenos erberi Saunders, male, cephalotheca, photomicrographs, SEM micrographs A frontal view B lateral view C vestigial antenna D frontal view E mouthparts. Abbreviations: fssf - furrow of supra-antennal sensillary field, mdt - mandibular tooth.