Platystethynium (Platystethynium) apteron Triapitsyn sp. n.

(Figures 1–3)

Type material

Holotype female on slide [MSNVE] (Figure 1 (a)), originally labelled: ‘ Italia, Veneto, Colli Euganei, Rovolon, 45.3628, 11.6505 [emerged] 20.X-6.XI.2022, from soil sampled 4.X.2022, leg. M. Uliana’. The type locality is 45°21 ʹ 46”N, 11°39 ʹ 02”E, at 218 m. The holotype (Figure 1 (b)) is complete and in good condition. Paratypes (same data as the holotype): 2 females on slides (UCRC), 159 females on points (2 at CNC, 145 at MSNVE, 2 at NHMUK, and 10 at UCRC), and 20 females in 95% ethanol stored in a freezer (UCRC, including two females under D#7421 that are primary DNA vouchers).

Etymology

The species epithet is a noun in apposition meaning wingless in Greek.

Diagnosis

Platystethynium (Platystethynium) apteron belongs to the onomarchicidum species group of P. (Platystethynium), as defined and keyed by Ortis et al. (2020). Its female differs from that of P. (Platystethynium) onomarchicidum by the features mentioned in the key above and by a much slenderer scape.

Description

Female (holotype, Figure 1 (b)). Mostly brown except frenum, propodeum, and appendages mostly lighter brown; pedicel and clava a little lighter than other antennomeres. Body strongly flattened dorsoventrally (as in Figures 2 (c) and 3(b)). Head (Figure 2 (a)) a little longer than wide (32:29); ocelli present and not enclosed by a stemmaticum, lateral ocellus almost touching supraorbital trabecula; mandibles reduced, not crossing over. Antenna (Figure 2 (b)) with short radicle fused to the rest of scape, scape smooth, 4.25 times as long as wide; pedicel longer than any funicular segment; F1 slightly shorter than F2, F1–F3 each slightly but clearly longer than wide, F3 the longest funicular, F4 about as wide as long, F5 just slightly smaller than F6 and both slightly wider than long, all funiculars without mps; clava markedly shorter than funicle, 2.9 and 3.1 times as long as wide (displaying a significant difference between the antennae), with 7 mps (2 on first, 2 on second, and 3 on third claval segments). Mesosoma smooth; midlobe of mesoscutum with a pair of adnotaular setae close to posterior margin; scutellum wider than long; frenum much wider than long. Apterous. Legs with femora slightly enlarged. Ovipositor short, occupying a little less than 0.4 length of gaster, 0.9 times length of metatibia, not exserted beyond gastral apex.

Measurements of the holotype (µm). Body: 806; head: 168; mesosoma: 210; gaster: 428; ovipositor: 163. Scape: 100; pedicel: 42; F1: 19; F2: 21; F3: 24; F4: 18; F5: 16; F6: 18; clava: 94.

Variation (paratypes, Figures 2 (c) and 3(a,b)). Body length of the specimens in ethanol 500–700 µm, of the dried-mounted specimens 460–620 µm, and of a slide-mounted specimen 750 µm.

Male unknown. However, existence of males is quite likely because female mandibles are reduced in this species (Figure 2 (a)). Thus, the unknown males of P. (Platystethynium) apteron are likely to be apterous like the conspecific females, and also likely to have enlarged heads and mandibles to chew emergence holes for their sisters while remaining within eggs of the host, like males of P. (Platystethynium) triclavatum (Ortis et al. 2020).

Distribution

Italy. Known only from the type locality.

Hosts

Uncertain. We attempted to find orthopteran eggs in the same soil sample from which P. (Platystethynium) apteron emerged, particularly those with parasitoid emergence holes similar to those made by P. (Platystethynium) triclavatum in parasitised eggs of Barbitistes vicetinus (Ortis et al. 2020, p. 6, fig. 3D and p. 8, fig. 4A). Eggs of two species of Tettigoniidae (Orthoptera), Barbitistes vicetinus and Eupholidoptera schmidti (Fieber), with exit holes of emerged parasitoids (Figure 4 (b,c)) were found in the same soil sample, so one or both of these (or, less likely, neither) are possible hosts of P. (Platystethynium) apteron. A definite rearing is needed because we do not know for certain whether they were parasitised by one or both species of P. (Platystethynium) occurring in the same area. No remains of any parasitoids, particularly males, were found inside these two eggs. Barbitistes vicetinus is the only known host of P. (Platystethynium) triclavatum (Ortis et al. 2020), so these two sympatric species of P. (Platystethynium) might utilise the same host egg resource.