Mesochorus (Stictopisthus) siamensis, Riedel, 2023

Riedel, Matthias, 2023, Contribution to the taxonomy of the Southeast Asian Mesochorinae (Hymenoptera, Ichneumonidae), Zootaxa 5245 (1), pp. 1-72 : 34-35

Mesochorus (Stictopisthus) siamensis nov. sp.

( Figs 6C , 12E , 19F , 24A )

Holotype. (♀) Thailand: Kauchanaburi, Microgasterinae cocoon, coll 8/99, em. 8/99, MR Shaw (Edinburgh).

Etymology. The species name is derived from the name “ Siam ”, a former name for Thailand.

Description. ♀: Body length 3.8 mm.

Head. Flagellum with 28 flagellomeres; 1 st flagellomere 6.0 × longer than wide and 1.6 × longer than 2 nd flagellomere, 0.6 × as long as eye; 2 nd flagellomere 3.6 × and preapical flagellomere c 2 × longer than wide. Temple distinctly and roundly narrowed behind eye, dorsally 0.6 × as wide as eye. OED 1.6 × and OOD 1.1 × ocellar diameter. Occipital carina complete medially. Frons smooth medially, with lateral microsculpture and fine curved paramedian ridges between antennal grooves. Face ( Fig. 12E ) coarsely punctate, 1.1 × wider than combined length of face and clypeus and 1.1 × wider than eye length, sides parallel. Mandible with two equal teeth. Malar space 0.6 × as long as width of mandibular base, finely striate. Genal carina reaching hypostomal carina far from mandibular base.

Mesosoma . 1.7 × longer than high. Mesoscutum with sparse and superficial punctures frontally and laterally, coarsely and densely punctate postero-medially, shining. Scuto-scutellar groove striate, narrow, 3.4 × wider than long. Mesopleuron with dense and coarse punctures ventrally. Dorsal end of epicnemial carina reaching frontal margin of mesopleuron. Propodeum ( Fig. 19F ) completely carinate. Area basalis trapezoid, wider than long. Area superomedia short, 1.5 × longer than wide and 0.9 × as long as area petiolaris; anterior transverse carina reaching at 6/10 of its length. Area petiolaris hexagonal, 1.1 × longer than wide. Hind femur 3.4 × longer than wide. Hind metatarsus 0.5 × as long as hind tibia and 2.9 × longer than 2 nd hind tarsomere. Hind claw apparently with one long basal tooth. Areolet sessile; vein 2m-cu slightly proximad its middle. Vein 1cu-a strongly postfurcal by about its length and inclivous. Postnervulus intercepted in its middle. Pterostigma 2.4 × longer than wide; distal part of RA (metacarp) only 0.7 × as long as width of pterostigma. Hind wing with 4 distal hamuli. Nervellus of hind wing vertical.

Metasoma. 1 st tergite 2.7 × longer than wide, postpetiolus distinctly striate. 2 nd tergite 1.1 × wider than long. Thyridium transverse, comma-shaped. Ovipositor sheath ( Fig. 24A ) stout, sparsely pilose, 6.3 × longer than wide and 1.0 × as long as hind metatarsus, pilose, slightly narrowed in apical 0.3.

Color. Body mainly yellow. Flagellum yellow in basal third, ochreous in distal 2/3. 1 st tergite reddish, yellow basally, with weak brownish spots postero-laterally. 2 nd tergite yellow, with two brownish baso-lateral stripes. 3 rd tergite yellowish in basal half, brownish apically. Following tergites and ovipositor sheath ochreous. Legs yellow; hind tibia narrowly infuscate in apical 0.1 (0.5 × tibial width). Hind tarsus ochreous. Pterostigma hyaline.

♁ unknown.

Taxonomical remark. Within the subgenus Stictopisthus , this new species is characterized by short distal part of the metacarp, confluent area basalis and area superomedia, whitish pterostigma and rather wide face.

Figures

FIGURE 6. Oriental Mesochorinae, habitus from lateral. A−Mesochorus semifuscus n. sp. HT, B−M. semipunctatus n. sp. HT, C−M. siamensis n. sp., D−M. stigmaticolor n. sp. HT, E−M. striatofacies n. sp. HT, F−M. sulaensis n. sp. HT.

FIGURE 12. Oriental Mesochorinae, face from frontal. A− Mesochorus sapaensis n. sp. HT, B−M. semifuscus n. sp. HT (♀), C−M. semifuscus n. sp. PT (♁), D−M. semipunctatus n. sp. HT, E−M. siamensis n. sp., F−M. stigmaticolor n. sp. HT, G−M. striatofacies n. sp. HT (♀), H−M. striatofacies n. sp. PT (♁).

FIGURE 19. Oriental Mesochorinae, propodeum from dorsal. A−Mesochorus rufator n. sp. HT, B−M. sabahensis n. sp. HT, C−M. sapaensis n. sp. HT, D−M. semifuscus n. sp. PT, E−M. semipunctatus n. sp. HT, F−M. siamensis n. sp. HT, G−M. stigmaticolor n. sp. HT, H−M. striatofacies n. sp. PT (♁), I−M. sumaterae n. sp. HT.

FIGURE 24. Oriental Mesochorinae, ovipositor sheath from lateral. A−Mesochorus siamensis n. sp., B−M. stigmaticolor n. sp. HT, C−M. striatofacies n. sp. HT, D−M. sulaensis n. sp. HT, E−M. sumaterae n. sp. HT, F−M. templator n. sp. HT, G−M. tenebris n. sp., H−M.