Pseudoxenos 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

Pseudoxenos Saunders, 1872

Pseudoxenos Saunders, 1872: 44. Type species: Pseudoxenos schaumii Saunders, 1872, by original designation.

Diagnosis of female cephalothorax.

Differs from Tuberoxenos by flat dorsal field of labrum (Fig. 41C ) and more flattened cephalothorax, with more or less even shape (Fig. 39C ), appearing flattened-elliptical in cross section. Distinguished from Deltoxenos by dorsal labral field laterally as long as along midline (Fig. 41C, D ), and meso-metathoracic segmental border not constricted laterally. In contrast to Macroxenos lateral parts of abdomen posterior to spiracles with dark coloration (Fig. 39D ). Mandible nested in mandibular capsule. In contrast to Paragioxenos , head and prothorax ventrally delimited by the birth opening in middle region and laterally by a suture.

Description of female cephalothorax.

Shape and coloration. Compact, longer than wide, elliptic in cross-section. Meso-metathoracic segmental border not constricted laterally. Size fairly constant, length 1.08-1.44 mm, maximum width 1.02-1.4 mm. Anterior head margin rounded or protruding. Thorax slightly widening posteriorly. Coloration with multiple brown shades forming pattern.

Head capsule. Ca. ⅖ as long as entire cephalothorax including lateral extensions. Coloration mostly dark brown, often with specific patterns. Clypeal region delimited from labral area (Fig. 41D ), arcuate, or protruding and forming clypeal lobe. Surface smooth or slightly wrinkled. Approximately 35-56 sensilla mainly concentrated anteriorly but dispersed over entire clypeal area. Border between clypeal area and frontal region hardly distinct but still recognizable. Frontal surface smooth (Fig. 40F ). Segmental border between head and prothorax clearly recognizable or indistinct on dorsal side, often indicated by dark brown stripes, and in some cases with two distinct dark spots on mesal region (Fig. 39D ).

Supra-antennal sensillary field. Smooth or slightly wrinkled, with dispersed sensilla. Furrow forming border on medial side more or less distinct (Fig. 41B ).

Antenna. Preserved as poorly defined area, sometimes raised, usually with several small, rounded plates, rarely with additional sensilla or cavity (Fig. 40C ). Periantennal area smooth.

Labrum. Ventral field distinctly wider than long, elliptic. Dorsal field nearly straight, slightly arcuate, at least 4-5 × wider than long in midline, flat and smooth, with 15-21 clearly visible setae inserted in cavities (Fig. 41C, D ). Dorsal field laterally as long as medially, in some cases almost merging with head capsule.

Mandible. Mandibles anteromedially directed at an angle of 35-45° and nested in mandibular capsule. Mandibular bulge not or slightly raised, bears several sensilla. Cuticle of mandible sculptured to nearly smooth. Mandibular tooth narrow, pointed, straight or hook-shaped, armed with spines.

Maxilla. Separated from labial area, slightly or distinctly protruding, prominent portion directed anteriorly or anterolaterally, maxilla slightly overlapping with mandible proximally (Fig. 41F ), but not projecting beyond it anteriorly. Cuticle usually smooth, rarely wrinkled. Vestige of palp very distinct, with more or less distinct plates or cavity, located medially on ventral side of maxilla. Submaxillary groove more or less distinctly produced posterolaterally to maxillary base.

Labium. Labial area between maxillae flat but distinct, relatively large, delimited anteriorly by mouth opening and posteriorly by birth opening. As long as wide or longer than wide. Cuticular surface in most cases largely smooth and shiny, or faintly and uniformly sculptured.

Mouth opening. Mouth opening arcuate, nearly straight, or bi-arcuate, sclerotized marginally.

Thorax and abdominal segment I. Pro-mesothoracic and meso-metathoracic borders more or less distinct, separated by mesal furrows. Border between metathorax and abdomen formed by ridge. Cuticle of thoracic segments on ventral side reticulate with scattered small and pigmented papillae. Cuticle of dorsal side of thorax smooth or slightly wrinkled. Prosternal extension undifferentiated, anterior margin evenly arched. Meso- and metathorax transverse. Lateral parts of abdomen posterior to spiracle dark (Fig. 39D ). Setae present on lateral region of abdominal segment I.

Spiracles. Spiracles on posterior ⅓ of cephalothorax slightly elevated, with anterolateral or lateral orientation.

Diagnosis of male cephalotheca.

Diameter of genae between maxillary base and compound eye ~ 1.5 × as large as diameter of vestigial antenna. Occipital bulge present (Fig. 42D ). Frontal region very distinctly deformed by frontal impression (Fig. 42D ). Distinct paired furrows of supra-antennal sensillary field absent.

Description of male cephalotheca.

Shape and coloration. In frontal view rounded laterally, flattened, elliptical, in lateral view pointed anteriorly. Coloration with pattern of pale and dark shades.

Cephalothecal capsule. Compound eyes with darker individual ommatidia well visible on pale ocular background. Clypeal lobe straight or slightly arcuate in frontal view, prominent in lateral view. Sensilla mainly concentrated medially. Frontal impression distinctly present (Fig. 42D ). Occipital bulge present (Fig. 42D ). Diameter of genae between maxillary base and compound eye small, ~ 1.5 × diameter of vestigial antenna.

Supra-antennal sensillary field. Kidney-shaped and bulging, delimited medially by frontal impression, without distinct furrows.

Antenna. Vestiges large, with complete torulus. Periantennal area not clearly delimited from supra-antennal sensillary field. Small plates or sensilla present (Fig. 27C ).

Labrum. Labral area distinct, with setae on dorsal field.

Mandible. Anteromedially directed. Mandibular bulge with sensilla, separated from pointed tooth.

Maxilla. Distinct, prominent. Coloration completely dark. Vestige of palp distinct.

Labium and hypopharynx. Labium distinct between and below maxillae, dark. Praementum and postmentum distinctly separated by furrow. Hypopharyngeal protuberance present.

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

Phylogenetic relationships.

Deeply nested within Xenidae ( Benda et al. 2019, 2021), part of a clade of an Old Word origin, with Tuberoxenos gen. nov. as sister group.

Diversity and distribution.

A group of Palearctic origin ( Benda et al. 2019), comprising seven currently valid species restricted to this region.

Hosts.

Various genera of Odynerini ( Vespidae : Eumeninae ).

Comments.

Pseudoxenos was described by Saunders (1872) but only a superficial description of the male was provided. Bohart (1937) synonymized many names previously designed ( Eupathocera , Ophthalmochlus , Homilops , Leionotoxenos Sceliphronecthrus, Macroxenos ) with Pseudoxenos . Although later Kinzelbach (1971b) used Pseudoxenos for all xenids parasitising solitary Vespidae worldwide, the genus corresponds to a Palearctic clade utilizing Odynerini according to the molecular phylogeny of Benda et al. (2019, 2021). We classify this lineage as a separate genus, based on these molecular phylogenic works and morphological characters newly reported here.

Figures

Figure 27. Leionotoxenos sp., male, cephalotheca, photomicrographs, SEM micrographs A frontal view B lateral view C vestigial antenna D frontal view E mouthparts. Abbreviations: fi - frontal impression, mx - vestige of maxilla, ob - occipital bulge.

Figure 39. Pseudoxenos sp., host, male, female, cephalothorax, photomicrographs A Paradontodynerus sp. stylopized by male of Pseudoxenos sp., lateral view B detail of host abdomen with male puparium inside C ventral side of female cephalothorax D dorsal side of female cephalothorax. Abbreviations: asI - abdominal segment I, sbhp - segmental border between head and prothorax.

Figure 40. Pseudoxenos 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. Abbreviations: a - vestigial antenna, fr - frontal region.

Figure 41. Pseudoxenos 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: dlf - dorsal field of labral area, fr - frontal region, fssf - furrow of supra-antennal sensillary field, mx - vestige of maxilla, sbhp - segmental border between head and prothorax, ssf - supra-antennal sensillary field.

Figure 42. Pseudoxenos sp., male, cephalotheca, photomicrographs, SEM micrographs A frontal view B lateral view C vestigial antenna D frontal view E mouthparts. Abbreviations: fi - frontal impression, ob - occipital bulge.