Pseudoneuroterus saltabundus Sottile & Cerasa sp. nov.

urn:lsid:zoobank.org:act: 8C6C6038-F9C6-469F-A7DC-FDDB327307C8

Figs 1–3, 7–8

Diagnosis

Among the asexual generations of species of Pseudoneuroterus, the only closely comparable species is the asexual generation of P. saliens. Pseudoneuroterus saltabundus sp. nov. can be distinguished by the following features: scape +pedicel 1.5 × as long as F1, which is 1.5× as long as the pedicel and nearly equal in length to F2 (Fig. 7G); the radial cell of the forewing (Fig. 8D) is 5.3 × as long as broad, and the prominent part of the ventral spine of the hypopygium (Fig. 8F–H) is short, only 2.3× as long as broad in ventral view, with long setae that extend beyond the apex of the spine. In contrast, in P. saliens (Figs 9, 10A–F), the scape + pedicel is 1.25 × as long as F1, which is 2.0 × as long as pedicel and 1.2 × as long as F2 (Fig. 9F–G); the radial cell is more than 6.0 × as long as broad, and the ventral spine (Fig. 10D–E) is at least 3.0 × as long as broad, with short setae that do not extend beyond the apex of the spine.

Etymology

Saltabundus is a participial adjective derived from the Latin verb ‘ saltare ’, meaning ‘to jump’ or ‘to leap’, formed with the suffix ‘-bundus’, which denotes a tendency or propensity to perform this action, referring to the characteristic jumping behaviour of these galls.

Type material

Holotype ITALY – Emilia-Romagna • ♀; Vernasca (PC); 44.7901° N, 9.7861° E; elev. 509 m; 1 Jun. 2024; ex galls on Quercus cerris; emerged 14 Jan. 2025; S. Sottile leg.; “Holotype Pseudoneuroterus saltabundus sp. n. Sottile & Cerasa” [(red) card-mounted]; MSNG S5421.

Paratypes ITALY • 1 ♀; same collection data as for holotype; emerged 14 Jan.–6 Feb. 2025; S. Sottile leg.; “Paratype Pseudoneuroterus saltabundus sp. n. Sottile & Cerasa” [white label]; MSNG S5422 • 1 ♀; same collection data as for holotype; same emergence data and label as for preceding; MCLSS-No.S5423 • 1 ♀; same collection data as for holotype; same emergence data and label as for preceding; JLN-A-No. S5424 • 2 ♀♀; same collection data as for holotype; same emergence data and label as for preceding; GCPC-No.S5425, GCPC-No.S5426 • 7 ♀♀; same collection data as for holotype; same emergence data and label as for preceding; SSPC-No.S5427 to S5433 • 1 ♀ (in ethanol); with same label; emerged 20 Jan. 2025; SSPC S5434.

Other material examined

ITALY – Emilia-Romagna • 1 ♀; Alseno (PC); 44.85247° N, 9.95203° E; elev. 140 m; 10 Jun. 2023; ex galls on Quercus cerris; emerged 13 Jan. 2024; S. Sottile leg.; SSPC S5181. – Lombardy • 1 ♀; Milano (MI), reforestation tree in the city park-Parco Nord Milano; 45.53099° N, 9.21267° E; elev. 130 m; 10 Jun. 2001; ex galls on Quercus cerris; emerged 14 Jan 2002; S. Sottile leg.; SSPC • 1 ♀; same data as for preceding; GCPC S722 (SAAF-GC HYM-7906).

Material used for molecular analysis

HUNGARY – Pest • 1 ♀; Gödöllő Arboretum; 12 Apr. 2016; ex bud gall on Quercus cerris; emerged 18 Apr. 2016: G. Csóka leg.; GenBank nos: PV820696 (cytb), PV836696 (ITS2).

ITALY • 1 ♀, paratype (in ethanol); same collection data as for holotype; emerged 20 Jan 2025; No.S 5435-saltab.18; GenBank nos: PV820703 (cytb), PV820709 (opsin), PV836697 (ITS2).

Additional sites where galls were observed

ITALY – Lazio • Leonessa (RI); 42.574514° N, 12.94764° E; elev. 940 m; 20 Apr. 2025; galls on Quercus cerris; S. Sottile leg. – Tuscany • Chiusdino (SI); 43.15350° N, 11.15454° E; elev. 280 m; 11 Aug. 2024; galls on Quercus cerris; S. Sottile leg. – Umbria • Sellano (PG); 42.890014° N, 12.89574° E; elev. 840 m; 1 Jul. 2024; galls on Quercus cerris; S. Sottile leg.

Type material examined

Syntypes of Neuroterus saltans [currently Pseudoneuroterus saliens] (Figs 9, 10A–F) Giraud’s type series of asexual females of N. saltans in the NHMW consists of 2 syntypes (one of them with crumpled wings) mounted on pins with the following labels: AUSTRIA • 2 ♀♀; “Type” [rectangular red label, printed] // “ Neur. saltans Gir. det. Giraud ” [white label, handwritten] // “Z.b. Gesellsch. Bd. IX. p. 337” [white label handwritten] [abbreviation for Verhandlungen der k.k. Zoologisch-Botanischen Gesellschaft in Wien volume, IX p. 337, journal in which the species was described] // “ NHMW-HYM #0029355 (NHMW)” [white label, printed]; NHMW.

Type locality: Austria, Giraud 1859: 337 (orig. descr.).

Description

Asexual female

BODY LENGTH. 1.55–1.8 mm (N = 18).

COLOURATION. Head brown, mandibles, maxillary palps and labial palps light brown; antennae brown, eyes black. Mesosoma brown, legs brown except distal third of hind coxae, proximal femur, proximal and distal tibiae which are yellowish brown. Metasoma brown. Wings hyaline, veins yellow-brown to brown.

HEAD (Fig. 7A–F). Nearly 1.35 times as broad as high in anterior view, 2.3 times as broad as long in dorsal view. Frons and vertex alutaceous to delicately coriaceous, with very rare white setae and small impression below median ocellus, eyes long with very rare minute setae; lower face coriaceous to imbricate, covered by sparse setae; malar space delicately coriaceous, without malar sulcus and striae (Fig. 7E–F). Clypeus small, smooth, rounded (Fig. 7E), marked by prominent epistomal sulcus; anterior tentorial pits and clypeo-pleurostomal line distinct, shallow, ventrally emarginated and deeply incised medially, ventral margin projecting over mandibles with long sparse setae on distal part (Fig. 7E–F). Malar space short, 0.32 times as long as height of compound eye. Transfacial distance 1.36 times as long as height of eye and 2.0 times as long as height of lower face (distance between antennal rim and tip of clypeus); diameter of torulus nearly equal to the distance between toruli; distance between torulus and inner margin of eye 1.40 times as long as diameter of torulus. Inner margins of eyes nearly parallel, slightly concave medially. Gena alutaceous to delicately coriaceous, very slightly broadened behind eye in frontal view (protrudes behind eye at least 0.1 times of transverse diameter of eye, measured in frontal view), covered in sparse setae. Ocelli elliptical in shape, elevated over dorsal margin of head; POL 1.5 times as long as OOL; OOL 2.67 times as long as diameter of lateral ocellus and 1.14 times LOL. Occiput alutaceous to delicately coriaceous with few white setae; postgena alutaceous to delicately coriaceous, with rare white setae, area around occipital foramen impressed and delicately alutaceous, devoid of setae. Postocciput around occipital foramen impressed; posterior tentorial pits ellipsoidal, narrow, deep (Fig. 7B); occipital foramen nearly equal to height of postgenal bridge, which is slightly shorter than length of oral foramen; gula smooth, glossy, as high as broad; gular sulci very weakly impressed, touching at base near hypostomal carina; median sulcus of postgenal bridge delicately impressed. Labial palpi 2-segmented, maxillar palpi 4-segmented. Antenna (Fig. 7G). filiform, with 12 flagellomeres, 1.22 times as short as body length, with sparse white setae on scape, pedicel and first six flagellomeres; setae gradually denser and shorter on the last six segments.

ANTENNA. Pedicel approximately as long as broad, F1–F3 nearly same thickness, F4–F8 nearly same thickness and thicker than previous, F9–F12 nearly same thickness and thickest. Pedicel and scape nearly 2.0 times as broad as F1–F3, 1.5 times as broad as F2–F5, 1.2 times as broad as F6–F8, 1.7 times as broad as F9–F12. Scape + pedicel 1.5 times as long as F1 which is nearly equal to F2; F1–F3 sub-equal in length; subsequent flagellomeres F4–F7 nearly equal in length and shorter than F1–F3; subsequent flagellomeres F8–F11 gradually decreasing in length; F12 nearly 1.8 times longer than F11. Placodeal sensilla present on F5–F12.

MESOSOMA. Very high, only 1.1 times as long as high. Pronotum glossy, with very few long white setae along antero-lateral edge and near pronotal spiracle, rare in other parts; anterior rim of pronotum narrow, emarginate; transverse pronotal sulcus present, deep with very few delicate striae near posteroventral corner of pronotum; posterolateral pronotal area, latero-median and median area of pronotum alutaceous to delicately coriaceous without rugae (Fig. 7H–J). Propleuron alutaceous, smooth, glossy with sparse long setae, slightly concave in mediocentral part (Fig. 7J–K). Mesoscutum smooth, glossy, with very rare white setae along its lateral margin and rare adnotaular setae; nearly as broad as long from above (width measured across base of tegulae); notauli absent, only faintly indicated by a sparse and discontinuous line of setae (Fig. 8A); median mesoscutal line absent; antero-admedian line absent, parapsidal lines absent; parascutal carina complete not sculptured median mesoscutal line absent; parascutal carina very narrow, mesoscutal suprahumeral sulcus very narrow and shallow. Transscutal articulation absent; mesoscutum fused with the mesoscutellum with boundary curved towards the mesoscutellum (Fig. 8A). Dorsomedian area of mesoscutellar-axillar complex (disc of mesoscutellum+axillar foveae) (Fig. 8A) nearly as long as broad from dorsal view, rounded, not elongated, not emarginated posteriorly and laterally; uniformly smooth and glossy, alutaceous medially with sparse long white setae, becoming delicately alutaceous at the extreme lateral areas; slightly overhanging metanotum; the part which overhangs metanotum is coriaceous to imbricate along lateral and posterior sides (visible in Figs 7I, 8C). Scutellar foveae (Fig. 8A) in the form of a transverse groove, more impressed than disk of mesoscutellum, with a smooth and glossy bottom, featuring weak wrinkles almost inconspicuous at low magnifications. Mesopleural triangle glossy with strong irregular wrinkles and few white setae. A well-defined ventral sulcus of the mesopleural triangle (Fig. 8B) is present, extending along about three-quarters of its ventral margin as a sharp-edged linear impression. Mesopleuron smooth, glossy to exceedingly faintly coriaceous, speculum entirely smooth, glossy and glabrous with very rare short white setae concentrated only close to the mesocoxal foramen. Pleurosternum smooth, glossy, with very delicate short wrinkles near mesocoxal foramina; acetabular carina indistinct, epicnemia broad, finely alutaceous. Metapleural sulcus distinct, reaching mesopleuron slightly above ½ of its height; preaxilla smooth and glossy with few delicate rugae; dorsal axillar area smooth and glossy to exceedingly faintly coriaceous with sparse long setae, lateral axillar area smooth, glossy to exceedingly faintly coriaceous without setae; axillar carina broad, with longitudinal striae; axillula triangular smooth and glossy without setae; subaxillular bar broad, smooth and glossy, at posterior end nearly equal in height to height of metanotal trough; propodeal spiracle very slightly elevated, ovate. Metascutellum (Fig. 8C) trapezoidal, smooth and glossy, nearly 1.75 times as broad as high and 2.0 times as high as height of ventral impressed rim of metanotum in posterodorsal view which is smooth; metanotal trough smooth, glossy, without setae, except for few setae in the upper external lateral corner of the metanotal trough in posterodorsal view. Lateral propodeal carinae absent, central propodeal area glabrous, smooth, glossy, with rare, faint microsculpture; lateral propodeal area smooth, glossy, with rare long white setae, nucha very short.

WINGS (Fig. 8D). Pubescent, 1.7 times as long as wide, hyaline, very weakly clouded around veins, 1.5–1.6 times as long as body, with distinct light brown veins and moderately long marginal setae (marginal setae length/forewing width = 0.11); radial cell open, 5.3 times as long as broad; R1 and Rs reaching wing margin and extending along it, R1 extending for half its length; first abscissa of radius (2r) curved, R1 longer than 2r; 2r–m straight; areolet distinct, triangular and large; 2r–m not extending along M vein; Rs+M distinct, reaching basalis vein at its middle height or slightly below. Hindwing (Fig. 8E), pubescent, 3.2 times as long as wide, hyaline, with very long marginal setae (marginal setae length/ hindwing width = 0.25), R 1 in the form of a narrow infuscate stripe on the anterior margin, starting from hamuli and extending along the margin for about 0.6 times the distance between the hamuli to the wing apex.

TARSAL SEGMENTS (Fig. 8I–K). All tarsal segments longer than broad, Ts1 the longest; hind tarsal claws simple, without basal lobe (Fig. 8K); fore tarsomere I (Ts1) to V (Ts5) length ratio as 1.0:0.35:0.3:0.2:0.55; tibial spur long, curved inward, bifid at apex, nearly 0.3 times as long as basitarsus of foreleg (Fig. 8I).

METASOMA. Nearly equal in length to mesosoma and nearly 0.8 times as short as head+mesosoma. Metasoma strongly compressed laterally, 0.7–0.8 times as long as high in lateral view, smooth, glossy, with rare and scattered white setae on T2 antero-laterally (Fig. 8F), all subsequent terga and hypopygium with micropunctures; T2 occupying nearly ½ length of metasoma. Prominent part of ventral spine of hypopygium pointed apically, ending in triangular shape, short, 2.3 times as long as broad in ventral view, and 0.09–0.1 times metasoma length in lateral view, with long white setae extending beyond apex of spine but never forming a tuft (Fig. 8F–H).

Asexual galls (Figs 1, 2A–F, 3)

The gall typically develops on the lower surface of Q. cerris leaves along the secondary veins, although in rare cases it has been observed on the upper surface as well; in the presence of 4–6 closely spaced galls, complete deformation and bending of the leaf lamina may occur (Fig. 1C). At the point of insertion, an invagination of the leaf blade is observed (Fig. 2F), while no conspicuous structures are present at the corresponding point on the upper surface, but rather a translucent ‘spot’ (Fig. 2E). At the insertion point, a thin membranous lamina expands in a fan-like manner and envelops the gall like a small shell; it is covered with star-shaped hairs similar to those on the leaf (Fig. 2B–D). This laminar structure is present only on one side of the gall and may perform a protective function in the early stages of gall development. In the mature gall, the lamina remains vestigial, reaching up to ¼, rarely ⅓ of its height. In rare cases, the lamina develops into a ribbon-like structure that encircles the gall (Fig. 2C). The lamina remains attached to the leaf after the main gall detaches, providing a remnant of the gall’s presence.

The main gall has a sub-globular ellipsoid shape, with a glabrous surface, traversed by very slight reliefs resembling venations (venulations) (Figs 2B, 3A). The thin (<0.1 mm), leathery walls (Fig. 3B, D) enclose a large larval chamber (Fig. 3B), excavated by the larva during the trophic phase. Typical dimensions are: longest side: 1.6–1.8 mm, shortest side: 1.3–1.5 mm, height: 1.4–1.6 mm. On the underside of the gall, the shape protrudes towards the point of insertion on the leaf blade (Fig. 2F); however, it is sessile with no peduncle present. The colour is whitish to pale green during development, and becomes light brown upon maturation.

Biology and host plants

Only the asexual generation is known. Galls develop along the secondary veins on the lower (rarely upper) surface of the leaves of Quercus cerris (Quercus section Cerris), the only known host species to date. Galls develop rapidly in late spring, between the end of May and mid-June, and generally complete development within approximately 7 to 10 days. Mature galls abscise from the leaf and remain in the moist litter during the following months. Rapid development and immediate abscission from the host leaf are likely advantageous traits favouring escape from parasitoid attack. Gall abscission is a process enhanced by the fully fed, mature larva, which is capable of performing rapid body extensions that facilitate detachment. The larva is positioned in a U-shaped posture within the gall chamber and, when externally stimulated, it abruptly extends its body, producing a rapid snapping motion (Supp. file 1). These contractions strike the internal walls of the gall, generating a distinct and audible “tick” sound perceptible to the human ear. The kinetic energy generated by these repeated strikes not only facilitates gall abscission, but also enables the remarkable jumping ability of the fallen galls (Supp. file 2), often exceeding distances of over 60 mm. The galls retain this jumping ability until September. Under laboratory conditions, jumping was consistently observed whenever the larvae were disturbed, either by gentle contact with a fine brush (Supp. file 3) or exposure to direct microscope lighting. We hypothesise that this active behaviour is triggered in the leaf litter whenever the larva perceives adverse environmental conditions, such as overheating due to sun exposure or contact with parasitoids attempting to oviposit through the gall wall. This behaviour is therefore interpreted as an escape mechanism, allowing the larva to relocate to potentially more favourable microhabitats. Galls that remain attached to the leaves are frequently parasitised by chalcidoid wasps or inhabited by inquiline Synergini Ashmead, 1896. Agamic females emerge during the second half of January and early February of the following year.

Similar galls

The asexual generation galls of Pseudoneuroterus saltabundus sp. nov. (Figs 1, 2A–F, 3) are similar in shape and size to the asexual generation galls of Neuroterus anthracinus (Curtis, 1838), but while the galls of the latter exhibit two symmetrical lamellar valves at the base (Fig. 11B–C) and possess a smooth and glossy surface with coloured maculae (Fig. 11A–B), the galls of the new species present only a single lateral lamella (Fig. 2B–D), and the surface is traversed by very slight elevations resembling venation and is matte (Figs 2B–C, 3A). Moreover, the agamic generation of N. anthracinus develops in the late summer–autumn on section Quercus oaks, whereas those of P. saltabundus develop in late spring (late May–mid-June) on section Cerris oaks.

The asexual generation galls of Dryocosmus destefanii Cerasa & Melika, 2018 (Fig. 11D–I) exhibit a similar size and shape, also develop in late spring, and share the same group of host plants (Quercus section Cerris). Phenological and morphological overlap, particularly in the case of mature galls (Fig. 11F, H–I) or those whose shape and size have been altered by the presence of parasitoids and inquilines, may lead to misidentification. However, those galls are covered with small protuberances, display a red to reddish colouration in the juvenile stage (Fig. 11D–E, G), and lack any lamellar processes developing from the base.

Asexual galls of P. saltabundus sp. nov. could be confused with those of its congener P. saliens. Galls of that species (Figs 10G–J, 11J–L) have a fusiform shape with a longer attachment base, larger dimensions, a smooth, almost shiny surface or with very fine parallel dorso-ventral striations, and develop along young stems or the leaf midrib. In contrast, P. saltabundus galls are rounder not fusiform, have a matte surface with characteristic venulation and typically develop on secondary veins (Figs 1A–B, 2A–D, F). Additionally, P. saliens galls develop in autumn rather than spring. Both galls exhibit the ability to jump, although this behaviour is less pronounced in P. saliens, as documented in Supp. file 4 (video recording). Distinguishing between these two species becomes difficult when galls are parasitised or atrophied during development.

Finally, the asexual generation gall of Cerroneuroterus minutulus (Giraud, 1859) (Fig. 11M–O) is also similar in size and shape to the asexual gall of P. saltabundus sp. nov. However, galls of C. minutulus display characteristic coniform protrusions on the surface and lack the lamellar process that develops from the base of P. saltabundus galls. Older galls of C. minutulus may show overlapping morphology and size with P. saltabundus galls, but microscopic examination of both external and internal structure can reliably differentiate these similar galls.

Distribution

The new species is currently recorded from northern Italy (Lombardy and Emilia-Romagna), peninsular Italy (Tuscany, Umbria, and Lazio) and Hungary.