Mesochorus britannicus, Schwenke, 1999

Riedel, Ravenhorst Matthias, 2018, Contribution to the Palaearctic species of Mesochorus G (Hymenoptera, Ichneumonidae, Mesochorinae): 1. The M. fulvus-group, Linzer biologische Beiträge 50 (1), pp. 687-716 : 691-692

Mesochorus britannicus SCHWENKE, 1999: 71 ( figs 5-8 )

Holotypus: (♀) Oxford 7.81, C 12 Denis OWEN (American Entomological Institute), typenot studied.

Description: ♀: Bodylength 5.5-7.5 mm. Flagellawith 37-41 segments, preapical flagellomeres c.2-2.5x longer than wide; 1 st flagellomeres length 6.0x width and 0.66x eye length; 2 nd flagellomeres length 4.2x width. Temples strongly and almost linearly narrowed behind eyes, length c.0.45-0.55x eye width. OOD 0.8-1.0. Face densely and coarsely punctate, width 1.0-1.1x length of clypeus+face and 0.8-0.9x eye length, with parallel sides. Clypeus with scattered punctures. Mandibels with two equal teeth. MI 0.3-0.4. Malar spaces, mandibular bases and ventral 0.3x of facial orbits striate. Occipital carina complete, rarely obsolete medially. Genal carinae reach the hypostomal ones far from mandibular bases (distance to bases c.0.7-1x length of malar spaces). Mesosoma densely pilose. Mesoscutum with scattered superficial punctures laterally and coarse dense punctures caudal-medially; mesopleura with fine and moderately dense punctures dorsally and with fine scattered punctures ventrally; metapleura with scattered superficial punctures. Area basalis narrowly trapezoid or rectangular, 2-2.5x longer than wide, rarely confluent with area superomedia, rarely with apical stalk; area superomedia slender, length c. 3.2-3.5x width and 1.85x length of area petiolaris, costulae in frontal 0.3; area petiolaris length 0.85x width. Hind femora length 5.3x height; hind metatarsi length 0.5x length of hind tibiae; apical fore tarsomeres not swollen, length 2.6-2.7x width; hind claws with rather short basal teeth, middle teeth longest. Areolets pointed, oblique, 2 nd recurrent veins proximal to their middle, nervuli interstitial; pterostigma length 3.7x width, radial veins in their distal 0.67. 1 st tergite length 2.9x width; postpetiolus length 1.35x width, smooth; 2 nd tergite length 1.05x width; thyridia large, roundish. Ovipositor sheaths densely pilose, slightly sabre-shaped, length 5.6-6.3x height and 0.75-0.8x length of hind metatarsi, moderately narrowed in apical 0.4.

Colour: Red. Head reddish; mandibular bases, malar spaces and ventral facial orbits usually cream-yellowish; ocellar field often more or less brownish. Mesosoma reddish; mesoscutum with two lateral and one fronto-medial reddish-brown longitudinal stripes; scutellum yellowish-red. Metasoma reddish; 1 st and 2 nd tergites slightly darker red. Legs reddish-yellow. Pterostigmata hyaline.

♂: Body length 6.5-7.5 mm. Flagella with 37-41 segments. Temples strongly but roundly narrowed behind eyes, length 0.55x eye width. OOD 0.8-1.0. Hind femora length c.5.4x height. Clasper stab-shaped, slightly clubbed apically, length 1.1-1.2x length of 2 nd hind tarsomeres. Structure and coloration as described for the ♀.

Hosts: Eulithris populata (LINNAEUS, 1758) (Lep. Geometridae ) via Cryptopimpla sp. (Hym. Ichneumonidae ).

Distribution: Austria*, Bulgaria*, Germany*, Kirgizstan*, Norway, Russia* (Tver and Arckhangelask regions), Sweden*, United Kingdom.

Figures

Figs 5-8: Mesochorus britannicus SCHWENKE ♀: (5) face, (6) propodeum, (7) distal fore tarsomere, (8) ovipositor sheaths.