Xenos, Rossius, 1793

Nain, Deepak, Rana, Anjali, Raychoudhury, Rhitoban & Sen, Ruchira, 2024, Morphology, biology and phylogeny of Xenos gadagkari sp. nov. (Strepsiptera: Xenidae): an endoparasite of Polistes wattii (Hymenoptera: Vespidae), Zootaxa 5493 (5), pp. 561-576 : 564-570

Results

Biological Note

P. wattii has a biannual nest founding strategy. In spring (March) the overwintered wasps initiate solitary foundress nests, which are abandoned within 2–3 months. In summer multiple females initiate nests, which last till October– November ( Sen et al., 2022). Xenos infections were spotted in wasps throughout their social cycle (March–December) as well as in hibernating wasps (December–February) (Nain et al. unpublished data). Nest-free aggregations of stylopised wasps were found in late April–May. In April 2015, a small cluster (10 wasps) of parasitized wasps were found in IISER-Mohali campus. It has been proposed that X. vesparum- infected P. dominula females cluster to facilitate the mating of the parasite ( Hughes et al., 2004a). Congruent with that hypothesis, both male (male pupa or empty puparium) and female Xenos were found in the aggregating wasps. As is typical in the case of most other strepsipterans, adult Xenos males eclose and leave the host while the neotenic females remain inside the host. Various developmental stages of the parasite were found in the wasps. Infected adult wasps with single or multiple parasites (Super-parasitism) ( Fig 1c , 2 ) were found in the nests during the late colony phase, in Oct–Nov ( Table 1 ).

Description

Male puparium

The male Xenos puparium is elongated and oval shaped. The texture of the puparium is different in the anterior and the posterior side—it is darkly sclerotized and shiny anteriorly (till the thorax) and light brown and dull posteriorly ( Fig 3 ). Length 4.53 ± 0.41 mm (n=7); Width 1.50 ± 0.13 mm (n=7). The anterior part is blunt and the posterior part bears the impression of the genitalia. Clear impressions of antennae, compound eyes (darkly sclerotized ommatidia) and mouthparts are visible through the puparium ( Fig 3–4 ). The labial part is protruding below the distinct frontal, clypeal and labral region ( Fig 4b ).

Adult Males ( Fig 5–6 )

Length: Length varies according to the available space in the host. In case of multiple infections, the males can be of different sizes ( Fig 3 ). Anterior to posterior end: 4.12 ± 0.6 mm (n=7).

Coloration: Body and legs are bright yellow (honey gold) in colour (matching with the host Polistes wattii’s colour). Antennae are darker than the body, almost brownish. Halteres and metathoracic wings are semitransparent, greyish (lint) in colour ( Fig 6 ).

Head: Hypognathus ( Fig 6 ), wider than the first two thoracic segments. Head width including the compound eyes: 0.634mm ± 0.054 (n= 6).

Compound Eye: Raspberry like eyes with protruding ommatidia/eyelets. Approximately 65–70 (68 in left eye 66 in the right eye of one specimen) ommatidia are present in each eye. Ommatidia are distinctly outlined with tufts of small hair or microtrichia ( Fig 7–8 ).

Antenna: Flabellate antenna with four segments—scape, pedicel and two segmented flagella. Scape and pedicel are of equal width. Flagellar segments are almost equal in length and width. The whole antenna bears minute hairs ( Fig 7 , 9 ).

Mouthparts: A pair of mandibles and maxillae are visible. Mandibles are elongated and blade-like. Maxillae are two-segmented. The distal segment is darker than the proximal segment ( Fig 10 , 11 ).

Prothorax: Pronotum is trapezoid in shape, elevated dorsally; the average length of pronotum is 0.066mm ± 0.01 (n=6), swollen with lateral depressions ( Fig 6 ).

Mesothorax: Mesonotum is visually wider than the pronotum and elevated dorsally (0.115mm ± 0.05, n=6. Fig 4 ). Forewings are modified into pseudo-halteres on both sides. Pseudohalteres are distally wide and bent both anterior and posteriorly into boat-like structures ( Fig 6 ).

Metathorax: Metathorax is more elaborate than the pro- and mesothorax. The average length of metanotum is 1.52mm ± 0.054 (n=6), Prescutum is pentagonal with a central longitudinal ridge and two depressions on both sides. Metathorax bears a pair of large fan-like wings (folded at rest) ( Fig 6 ).

Legs: Fore, mid and hind legs are made of coxa, trochanter, femur, tibia and tarsus with four tarsomeres. Pretarsus is absent. All tarsomeres have hairy, oval, adhesive pads. The first tarsomeres of all legs have a pit ( Fig 13 ).

Abdomen: 8-segments are clearly visible, terminal segments are modified into genitalia ( Fig 6 ).

Neotenic Female

The female body size varies between hosts. Body length is 8.52mm ± 0.90 (n=6). Cephalothorax width is 1.38mm ± 0.13 (n=7), abdominal width is 2.22mm ± 0.23 (n=7). Colour: Cephalothorax dark brown, abdomen creamy white-light yellow with a central birthing canal with variable numbers of planidium larvae, which are clearly visible through the transparent cuticle of cephalothorax and abdomen, Fig 14–15 ). The brood canal can be white or light brown before the hatching of the planidium larva but they appear darker brown with the increasing number of maturing larvae ( Fig 14 ). The cephalothorax of the female ( Fig 15 ) is described further under the differences with X. hebraei and X. vesparum .

Planidium Larva

Varied numbers of first-instar planidia larvae were found inside the neotenic female ( Fig16a ). Planidia larvae are approximately 200µm in length from anterior to posterior end. They are characterized by sclerotized exoskeleton, two black eyespots and two pairs of caudal setae ( Fig 16b ).

Figures

FIGURE 1. (a) Nest of P. wattii; (b) A healthy female P. wattii. (c) Male X. gadagkari (d) Abdomen of a stylopized P. wattii, infected with a male and a female X. gadagkari (e) Female X. gadagkari.

FIGURE 2. Abdomen of a female wasp with double infections (2a, b) and triple infections (2c, d). Left panel: Before sclerite removal, Right panel: After sclerite removal.

FIGURE 3. a. Puparia collected from a triple infected wasp (shown in Fig 2c and 2d). The anterior sides, represented by the dark brown, translucent cuticle are directed downward. 3b. Males dissected out of the puparia shown in 3a.

FIGURE 4. a.SEM imageof the male puparium b. SEM image ofthe cephalotheca of the male puparium showingthe impressions of the mouthparts and antenna. COE—Compound eye, AN—Antenna, FR—Frontal region, CL—Clypeus, DLF—Dorsal labral field of labral area, VLF—Ventral labral field of labral area, OS—Mouth opening, HYP—Hypopharynx, PRM—Prementum, POM—Postmentum, MD—Mandible, MX—Vestige of maxilla.

FIGURE 5. Male X. gadagkari eclosed naturally from the puparium.

FIGURE 6. a Live male X. gadagkari taken out of puparium. b. Illustration of a male X. gadagkari. PRN—Pronotum, AC— Acrotergite, MN—Mesonotum, PC—Prescutum, SL—Scutellum, POL—Postlumbium, PN—Postnotum, FW—Forewing, HW—Hindwing.

FIGURE 7. a and b. Compound eye and Flabellate antenna in male X. gadagkari. AN—Antenna, COE—Compound eye, OM—Ommatidia.

FIGURE 8. SEM image of the compound eye of male X. gadagkari.

FIGURE 9. SEM image of the antenna of male X. gadagkari.

FIGURE 10. Ventral view of the male X. gadagkari.

FIGURE 11. Mouth parts of male X. gadagkari.

FIGURE 13. a. Proleg, b. midleg and c. hindleg of male X. gadagkari. d. Illustrations of the corresponding legs on the left.

FIGURE 14. a. Fertilized female X. gadagkari with planidia larvae collected from P. wattii. b. Illustration of female X. gadagkari. CT—Cephalothorax, BC—Brood canal.

FIGURE 15. a. Cephalothorax of female X. gadagkari with planidia larvae collected from P. wattii. b, c and d SEM images of the female cephalothorax. SBHP—Segmental border between head and prothorax, PL—Planidium larvae, OS—Mouth Opening BC—Opening of the Brood Canal, SES—Semicircular field possible of labral region, MX—Maxilla, MD—Mandible.

FIGURE 16. a. Planidia larvae inside the cephalothorax and emerging through the gonopore of female X. gadagkari. b. Illustration of a planidium larva.