Chalybion tanvinhensis Pham & Ohl, sp. nov. (Figs. 1‒10)

Material examined: Holotype, ♀, pinned (deposited in IEBR, VAST), VIETNAM: Hoa Binh, Tan Vinh, Luong Son, 2.v.2017, Phong Huy Pham [IEBR] . Paratypes (IEBR, VAST): VIETNAM: Son La: 2 ♂♂, Chieu Village, Muong Thai, Ham Yen, 11.viii.2017, Phong Huy Pham [IEBR] .

Diagnosis: Chalybion tanvinhensis is a member of the C. fabricator species-group because of the following combination of characters: Anterior margin of clypeus with five distinct teeth (median three close together, lateral teeth sharp and rather distant from others), integument dark blue, tarsi without plantulae, lower metapleuron area without angular carina, a rim at propodeal base only behind metanotum, metapleuron distinctly depressed below level of mesopleuron and side of propodeum, sixth metasomal sternum of female flat and apically broadly truncate.

This species can be easily distinguished from the other seven species of the C. fabricator species-group known so far by the following combination of characters: forewing homogenously, light brownish; fourth metasomal sternum of female without micropubescence; median and submedian teeth of clypeus well separate; vertex finely, sparsely punctate; mesoscutum weakly transversely strigose, interspaces shallowly punctate; petiole markedly curved, much shorter than the hindbasitarsus; antenna black; mesopleuron coarsely, densely punctate; metasoma with violaceous reflections. Because males of the fabricator species-group are known only for C. hainanense, C. malignum and C. sulawesii, the male of this new species can easily be separated from them by having the clypeus without teeth and no placoids on seventh to ninth flagellomeres.

This new species is similar to C. lividum and C. sulawesii, but it can be distinguished from the first by having black antenna, the median tooth of the clypeus much narrower than submedian teeth, the metasoma with violaceous reflections; from the latter by having lateral teeth of the clypeus in the female rather sharp; the forewing slightly, rather unevenly brownish; the medial and submedial cells most uniformly hyaline; petiole markedly curved, much shorter than the hindbasitarsus.

The male of C. tanvinhensis is unique in Chalybion in having the following characters: clypeus without lateral tooth, median and submedian tooth fused into single protruding lobe, placoids on seventh to ninth flagellomere (similar to C. japonicum (Gribodo, 1882), C. ohli Dollfuss, 2016 and C. zimmermanni Dahlbom, 1843).

Description:

Female (Figs. 1‒6): Body length 20 mm, forewing length 15 mm.

Head (Fig. 1): In frontal view subcircular, about 1.23 times as wide as high. Mandible with inner subapical tooth. Clypeus moderately convex, without median carina; anterior margin of clypeus with five distinct teeth: lateral tooth, separated distantly from submedian tooth, narrow and sharp; submedian tooth blunt, broader than median and lateral teeth, and as long as median tooth. Frontal line present. Ocelli not reduced; distance between hindocelli about equal to that from hindocellus to inner eye margin and about 0.43 times that from hindocellus to vertex margin. Clypeus coarsely, sparsely punctate. Frons coarsely, irregularly transversely punctatorugose. Vertex and gena finely, sparsely punctate. White setae sparse on clypeus, denser than on gena. Lower inner orbit area with moderately dense pubescence. Flagellar ratio (length of the first flagellomere divided by that of the second flagellomere) 0.82; orbital ratio (shortest interocular width across vertex divided by shortest interocular width across clypeus) 0.83; clypeal ratio (length of clypeus divided by shortest interocular width across clypeus) 0.82; hypostomal cavity ratio (length of hypostomal cavity divided by width) 0.89.

Mesosoma (Figs. 2‒5): In dorsal view, width between tegulae equal to that of pronotum at midlength. Pronotum with notch at middle and series of transverse striae anteriorly. Mesoscutum moderately transversely striate, interspaces shallowly punctate; mesopleuron coarsely, densely punctate. Scutellum, metanotum, and upper metapleural area rather coarsely, densely punctate. Lower metapleuron conspicuously, transversely striate. Dorsal propodeum coarsely, transversely striate; side of propodeum punctate-reticulate. Mesosoma ratio (length of mesosoma divided by height) 2.18.

Metasoma (Figs. 5‒6): Integument smooth, shiny, with silvery pubescence. Petiole conspicuously curved. Metasomal sternum IV without micropubescence. Petiole much shorter than hindbasitarsus. Petiole-basitarsal ratio (length of petiole divided by that of hindbasitarsus) 0.70.

Color: Integument dark blue. Mid and hind legs, propodeum and metasoma with violaceous reflections; antenna black except scape and pedicel dark blue. Mandible, labial palpus and maxillary palpus black. Forewing slightly, rather unevenly brownish, medial and submedial cells mostly uniformly hyaline, infuscate at apex (Figs. 3‒4). Hindwing hyaline, somewhat infuscate at apex (Fig. 4).

Male (Figs. 7‒10): Body length 14.5-15.5 mm, forewing length 10.5 mm.

Structure as in female, but differing as follows:

Head (Fig. 7): Mandible without inner subapical tooth. Clypeus without teeth, median and submedian tooth fused into single protruding lobe. Distance between hindocelli 0.62–0.67 times that from hindocellus to inner eye margin and about 0.31–0.33 times that from hindocellus to vertex margin; antenna with placoids on seventh to ninth flagellomeres. Flagellar ratio (length of the first flagellomere divided by that of the second flagellomere) 0.89–0.94; orbital ratio (shortest interocular width across vertex divided by shortest interocular width across clypeus) 0.93–0.97; clypeal ratio (length of clypeus divided by shortest interocular width across clypeus) 0.60–0.67; hypostomal cavity ratio (length of hypostomal cavity divided by width) 0.89–0.96.

Mesosoma (Figs 8‒9): Mesopleuron coarsely, densely punctatorugose. Posterior propodeal surface coarsely, densely punctate-reticulate. Mesosoma ratio (length of mesosoma divided by height) 2.18–2.21.

Metasoma (Figs. 9‒10): Metasomal sterna IV and V with large patch of micropubescence. Petiole-basitarsal ratio (length of petiole divided by that of hindbasitarsus) 0.58–0.64.

Etymology: The specific name of this species refers to the type locality, Tan Vinh Commune.

Distribution: Vietnam: Hoa Binh, Son La

Notes on nest (Fig. 16): A single nest of the new species that we found was collected in a desolate house at Chieu Village, Muong Thai Commune, Ham Yen District, Son La Province on 11 August 2017. This house, abandoned around two years ago, was on the gently sloping surface of a low large mountain, 300 m from the strictly protected secondary forest (Ta Xua Natural Reserve). This area which is an edge of the Ta Xua Natural Reserve was used to cultivate some plants such as dry rice and cassavas. The nest found here was made from mud and was attached against a wood-made house pole, 2.2 m from the ground and consisted of two cells. The cells were ovalshaped, 20 mm long, 12-14 mm wide in the middle. The inside of the cells was flat, smooth, the outside rough. The wall of cells was around 1-2 mm thick. The nest was not covered by mud layers but only on one side several mud pieces were added. This appears to make solidly-built nest foundations and firmly stuck nest body on the house pole. These characters of the nest structure are different from those of other sphecid wasps or eumenid wasps, for example, the genus Sceliphron, the genus Delta, or the genus Phimenes . To our knowledge this was possibly a nest of Pompilidae . Each nest cell with an original emergence hole which was sealed by mud and added a layer of brown unknown material on the outside indicates that tanvinhensis reuses this old nest. This is a characteristic feature of the genus Chalybion .

Two males from the nest taken and reared under laboratory conditions emerged on 28 and 29 August 2017, respectively. Because no nest dissection was made, the nest content remains unknown and only fragments of dark brown cocoon shells of tanvinhensis remaining in the two cells were found after emergences.

On 2 May 2017 a single female of the species was caught in a desolate house at Tan Vinh Commune, Luong Son District, Hoa Binh Province, while she was searching old nests of Sceliphron madraspatanum on the house walls. Chalybion tanvinhensis is rare in its nesting habitats, and it is, hence, impossible to take more specimens at these sites despite several hours spent there.