Sphecixenos, Benda & Pohl & Nakase & Beutel & Straka, 2022

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

Sphecixenos gen. nov.

Type species.

Paraxenos orientalis Kifune, 1985, here designated.

Diagnosis of female cephalothorax.

Differing from all other genera of Xenidae by very distinct prosternal features: prosternal extension anteriorly with very conspicuous, extensive pale spot, sometimes associated with cuticular impression (Figs 35C , 37A ). A feature linked with the maxillae is shared with Paraxenos or Tuberoxenos : submaxillary groove distinctly produced posterolaterally to maxillary base (Fig. 37A ), extending along cephalic border distally and then connected to border between head and prothorax. 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, ca. as long as wide, or slightly longer. Size variable, length 0.96-1.64 mm, maximum width 0.9-1.8 mm. Anterior head margin rounded, not protruding. Thorax slightly widening posteriorly. Abdominal segment I sometimes protruding laterally, forming rounded corner below spiracles. Coloration never completely pale, comprising multiple brown shades forming distinct patterns.

Head capsule. ~ ⅓ ~ ⅖ as long as entire cephalothorax including lateral cephalic extensions. Combination of pale and dark brown shades resulting in specific color pattern. Clypeal region well delimited from labral area, arcuate, without or with slightly protruding clypeal lobe. Surface smooth or slightly wrinkled. Sensilla (> 30) better visible in dorsal view than ventrally, concentrated mainly on anterior clypeal area. Border between clypeal region and frontal area indistinctly recognizable. Frontal area smooth or slightly reticulated. Dorsal border between head and prothorax indicated by interrupted suture or distinctive coloration, or scarcely recognizable.

Supra-antennal sensillary field. Smooth or slightly wrinkled, with evenly dispersed sensilla, not delimited or indistinctly delimited by furrow medially (Fig. 37B ).

Antenna. Preserved as poorly defined area with several small, rounded plates, cavity, or sensilla. Periantennal area smooth (Fig. 36C ).

Labrum. Ventral field wider than long, elliptic. Dorsal field slightly arcuate, 3-4 × wider than long in midline. Dorsal field with several inconspicuous setae, usually blunt, not pointed.

Mandible. Mandibles anteromedially directed at angle of 35-55°, enclosed in mandibular capsule. Mandibular bulge rounded or pointed, with several sensilla. Cuticle smooth, with longitudinal grooves. Tooth narrow, armed with spines.

Maxilla. Variable in shape, in some cases reduced and fused to labium, otherwise well-developed, separated from labial area, anteriorly directed, prominent but not projecting beyond mandible. Cuticle finely reticulated. Vestige of palp present as cavity with accessory plates or reduced. Submaxillary groove distinctly produced posterolaterally to maxillary base extending along cephalic border (Fig. 37A ).

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

Mouth opening. Distinctly arcuate to nearly straight, sclerotized marginally.

Thorax and abdominal segment I. Pro-mesothoracic and meso-metathoracic borders relatively distinct, indicated by mesal furrows combined with stripes of specific coloration. Border between metathorax and abdomen usually indicated by change in cuticular surface structure or pigmentation. Cuticle of thoracic segments on ventral side reticulate with scattered small and pigmented papillae. Cuticle of dorsal side of thorax indistinctly reticulated. Prosternal extension differentiated anteriorly, with very conspicuous extensive pale spot, sometimes associated with cuticular impression (Figs 35C , 37A ). Shape of meso- and metathorax unmodified, transverse. Setae on lateral region of abdominal segment I (Fig. 36E, F ) present, or cuticular surface distinctly sculptured.

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

Diagnosis of male cephalotheca.

Differing from other genera by large diameter of genae between maxillary base and compound eye, at least 2 × as large as diameter of vestigial antenna. Distinct paired furrow of supra-antennal sensillary field absent. Cephalotheca nearly circular in frontal view (Fig. 38A ). Diameter of vestigial antennae smaller than width of medially directed mandible (Fig. 38E ).

Description of male cephalotheca.

Shape and coloration. In frontal view rounded, nearly circular, in lateral view rounded or slightly pointed anteriorly. With pattern of multiple shades of brown.

Cephalothecal capsule. Compound eyes with dark individual ommatidia well visible on paler ocular background. Clypeal lobe straight in frontal view, slightly protruding in lateral view. Sensilla mainly concentrated on medial clypeal region. Frontal impression indistinct. Occipital bulge absent. Diameter of genae between maxillary base and compound eye large,> 2 × as large as diameter of vestigial antenna.

Supra-antennal sensillary field. Kidney-shaped and bulging, distinctly developed. Lacking distinct furrows medially.

Antenna. Of standard shape but very small, with small plates or cavities and complete torulus (Fig. 38C ). Periantennal area not clearly delimited from supra-antennal sensillary field.

Labrum. Labral area distinct.

Mandible. Rather medially directed than anteromedially. Mandibular tooth pointed, not reaching area of mandibular bulge basally.

Maxilla. Distinct, prominent, with entirely dark coloration. Vestige of palp distinct.

Labium and hypopharynx. Dark labium distinct between and below maxillae. Praementum and postmentum separated by furrow. Hypopharyngeal protuberance not present.

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

Phylogenetic relationships.

According to Benda et al. (2019, 2021) sister to a monophyletic lineage containing Pseudoxenos and Tuberoxenos gen. nov.

Diversity and distribution.

This genus represents a lineage of Afrotropical origin which dispersed to Australia ( Benda et al. 2019). It currently comprises 12 species, distributed in the Old World (mainly Afrotropical and Oriental regions) and Australian region.

Hosts.

Sphex , Isodontia ( Sphecidae : Sphecinae ), Sceliphron ( Sphecidae : Sceliphrinae ), and Chlorion ( Sphecidae : Chloriontinae ).

Etymology.

The name is derived from the family Sphecidae , the only known host family of this genus. The ending - xenos is used in several generic names, mainly in the family Xenidae . It is from a Greek substantive meaning enemy or stranger. Gender masculine.

Comments.

All described species of Sphecixenos gen. nov. were previously placed in Paraxenos based on parasitising digger wasps ( Kinzelbach 1971b). Despite this concept, this group is morphologically well defined. We classify it as a separate genus, based on the molecular phylogeny ( Benda et al. 2019, 2021) and morphological characters newly reported here.

Figures

Figure 35. Sphecixenos orientalis, host, female, cephalothorax, photomicrographs A Sceliphron madraspatanum stylopized by female of S. orientalis, lateral view B detail of host abdomen with adult female inside C ventral side of cephalothorax D dorsal side of cephalothorax. Abbreviations: mxb - maxillary base, pps - prosternal pale spot.

Figure 36. Sphecixenos orientalis, 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 right lateral border of abdominal segment I below spiracle, dorsal side. Abbreviations: a - vestigial antenna, paa - periantennal area.

Figure 37. Sphecixenos orientalis, 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: fr - frontal region, fssf - furrow of supra-antennal sensillary field, pps - prosternal pale spot, sbhp - segmental border between head and prothorax, smxg - submaxillary groove, ssf - supra-antennal sensillary field.

Figure 38. Sphecixenos cf. gigas, male, cephalotheca, photomicrographs, SEM micrographs A frontal view B lateral view C vestigial antenna D frontal view E mouthparts. Abbreviations: a - vestigial antenna, md - mandible, mx - vestige of maxilla.