Sakhalinoctonus Davidian, 2021

Davidian, Elena M., Manukyan, Andranik R. & Belokobylskij, Sergey A., 2021, A new genus and species of the aphid parasitoids (Hymenoptera: Braconidae: Aphidiinae) from the Eocene Sakhalinian amber, Palaeoentomology 4 (6), pp. 537-543 : 538-542

Genus Sakhalinoctonus Davidian , gen. nov.

Type species. Sakhalinoctonus alexrasnitsyni Davidian , sp. nov.

Etymology. The new genus name is composed from Sakhalin, name of island where the studied amber was collected, and part of the aphidiine genus name “ Monoctonus ”. The gender is masculine.

Diagnosis. Mandible bidentate; maxillary palpus 4-segmented. Antenna ( Fig. 2 ) 12-segmented, filiform, densely pubescent. Mesoscutum ( Figs 1 , 2 ) probably with complete notauli. Propodeum with large median areola delineated by prominent carinae. In forewing ( Fig. 3A, B ), pterostigma narrowly triangular; metacarpus (1-R1) relatively hardly perceivable, not reaching wing apex. Radial (r, 3-SR, SR1), medial (1-SR+M, 2-M, 3-M) and parallel(CU1a) veins of forewing long and almost reaching distal margin of wing. First and second radiomedial (submarginal) cells fused together with discoidal (discal) cell and formed united large medial cell. Second transverse anal vein (a) present, but very fine. Hind wing without closed cells. Legs ( Figs 1 , 2 ) long; hind leg about as long as body, covered by dense and semi-erect setae (as those on body). Petiole of metasoma ( Figs 1 , 2 ) long, slightly widened towards apex, about 4.0 times as long as its width medially. Ovipositor weakly curved down, wide basally, acuminate towards apex and with subapical dorsal notch. Ovipositor sheath ( Fig. 3C ) relatively long, about 6.0 times longer than maximum width, gradually tapered from base towards apex and very narrowly rounded at apex, weakly curved downward, covered by mainly long setae.

Remarks. Sakhalinoctonus gen. nov. is the most similar to the fossil genera Protacanthoides Mackauer, 1961 (type species: Trioxys obscuriformis Quilis, 1940 = Trioxys fossilis Mackauer, 1959 ) and Promonoctonia Starý, 1973 (type species: Aphidius quievreuxi Quilis, 1940 ) by the small number of antennal segments, presence of the closed medial cell in the forewing, and downward curved and taped apically ovipositor sheaths.

Protacanthoides and Promonoctonia are characterised by a 13-segmented thick antenna, third abscissa of radial vein (SR1) of forewing rather short and not reaching distal margin of wing, second (3-SR) and third (SR1) abscissae of radial vein subequal in the length, and the ovipositor sheath curved downward. In addition, Protacanthoides fossilis has metasomal petiole subtriangle with approximately equal its length and maximum width, which is smooth and without protruding spiracular tubercles; ovipositor sheath rather short, evenly curved downward and tapered towards its apex, acuminate apically, about 0.15 times as long as metasoma. Unfortunately, the information about the condition of notauli, propodeum and pubescence of the ovipositor sheath was not visible in this specimen. On the other hand, Promonoctonia quievreuxi is also characterised by the following additional features: notauli missing; propodeum smooth and without delineated areola; metasomal petiole very short and wide; ovipositor sheaths claw-shaped, with long and wide its basal part and short and narrow apical part, approximately 3.0 times longer than its maximum width and 0.15 times as long as metasoma.

The differences between Sakhalinoctonus gen. nov. and similar fossil genera are shown in the key below.

Key to fossil aphidiine genera with curved down ovipositor sheaths

1. Antenna slender, 12-segmented ( Fig. 2 ). Third abscissa of radial vein (SR1) and second abscissa of medial vein (2- M) of forewing long and almost reaching distal margin of wing ( Fig. 3A ). Ovipositor sheaths ( Fig. 3C ) relatively long and curved downward, gradually tapered towards apex, very narrowly rounded at apex, about 6.0 times longer than its maximum width and 0.4 times as long as metasoma................................... Sakhalinoctonus gen. nov.

- Antenna thick, 13-segmented. Third abscissa of radial vein (SR1) and second abscissa of medial vein (2-M) of forewing short and far from reaching distal margin of wing. Ovipositor sheaths short, claw-shaped and with long widened basal part and short narrow apical part, or evenly tapered to apex and acuminate apically, about 3.0 times longer than its maximum width and 0.15–0.20 times as long as metasoma...................................................................... 2

2. Ovipositor sheaths claw-shaped, with long and wide its basal part and short and narrow its apical part, perhaps narrowly rounded apically. [Mesoscutum without notauli. Propodeum without delineated areola. Petiole of metasoma very short and wide] ......................... Promonoctonia Starý

- Ovipositor sheaths weakly curved downward, gradually tapered from base to apex and acuminate apically. [Petiole of metasoma subtriangular, smooth, without projecting spiracular tubercles, about as long as its maximum width].. ................................................... Protacanthoides Mackauer

Key to fossil Sakhalinoctonus gen. nov. and the most similar extant genera

1. Ovipositor sheaths curved down, gradually tapered towards apex and acuminate apically. Antenna 11–14- segmented..........................................................................2

- Ovipositor sheaths straight and strongly acuminate apically or weakly upcurved, weakly tapered and obtuse apically. Antenna 14–17-segmented ............................................... 4

2. Ovipositor sheaths approximately 3.0 times longer than its maximum width, entirely uniformly covered by long and sparse setae. Antenna 12–14-segmented. [Propodeum with medial areola. Petiole of metasoma parallel-sided, sculptured, with medial longitudinal carina, 3.0 times longer than width at level of spiracles. Long setae of ovipositor sheaths arranged mainly along its dorsal margin]............................................ Calaphidius Mackauer

- Ovipositor sheaths 6.0–7.5 times longer than its maximum width, uniformly covered by numerous long setae longest on its ventral margin or covered by short and numerous setae on dorsal margin of sheaths and sparse and long setae on their ventral margin.Antenna 11–12-segmented. [Petiole of metasoma weakly widened toward apex or almost parallelsided, with weakly protruding spiracular tubercles]......... 3

3. Antenna 12-segmented. Forewing with closed medial cell. Third abscissa of radial (SR1) and second abscissa of medial (2-M) veins long and almost reaching distal margin of wing. Ovipositor sheaths covered almost uniformly with long setae, longest on ventral margin; sheaths 6.0 times longer than its maximum width. Propodeum with central area delineated by high carinae. Petiole of metasoma weakly widened toward apex, 4.0 times longer than its maximum width ......................................... Sakhalinoctonus gen. nov.

- Antenna 11-segmented. Forewing with open medial cell. Third abscissa of radial (SR1) and second abscissa of medial (2-M) veins short and far not reaching distal margin of wing. Ovipositor sheaths covered by short and dense setae on their dorsal margin and long and sparse setae on their ventral margin; sheaths approximately 7.5 times longer than its maximum width. Propodeum basally only with two short and divergent posteriorly carinae, without delineated central area. Petiole of metasoma almost parallel-sided, 2.0 times longer than its medial width.......... Indaphidius Starý

4. Ovipositor sheaths straight,distinctly acuminate apically,3.0 times longer than its maximum width. Antenna moniliform, 14–15-segmented. Propodeum without carinae. Petiole of metasoma short and wide, about as long as its width at level of spiracular tubercles................................ Aclitus Foerster

- Ovipositor sheaths weakly upcurved, weakly tapered towards apex and obtuse apically, 2.0 times longer than its maximum width. Antenna filiform, 17-segmented. Propodeum basally with two divergent posteriorly carinae. Petiole of metasoma long and rather narrow, 3.5 times longer than its width at level of spiracular tubercles.......... .......................................... Archaphidus Starý & Sсhlinger

Figures

FIGURE 1. Sakhalinoctonus alexrasnitsyni gen. et sp. nov., holotype, PIN 3387/104. Habitus (camera Canon EOS 70D).

FIGURE 2. Sakhalinoctonus alexrasnitsyni gen. et sp. nov., holotype, PIN 3387/104. A and B, Body, in different type of accent light (camera Canon EOS 70D).

FIGURE 3. Sakhalinoctonus alexrasnitsyni gen. et sp. nov., holotype, PIN 3387/104. A, Forewing, drawing. B, Distal part forewing (camera Canon EOS 70D). C, Ovipositor and sheaths (camera Axio Imager M-1 Carl Zeiss microscope).