Lysitermus pallidus Foerster, 1863

Achterberg, Cornelis van, Skeppstedt, Fredrik & Vaeaenaenen, Simo, 2021, Revision of the Palaearctic species of Lysitermus Foerster (Hymenoptera, Braconidae, Hormiinae), ZooKeys 1040, pp. 65-89 : 68-72

Lysitermus pallidus Foerster, 1863 Figs 1 , 2-8 , 9-11 , 26

Lysitermus pallidus Foerster, 1863: 236; Shenefelt 1975: 1155; Belokobylskij and Tobias 1986: 64; van Achterberg 1991: 20; Gupta and Quicke 2018: 429.

Material.

5 ♀ + 1 ♂ (= type series of L. pallidus ; ZMB), "[ Germany], Aachen ", “Frst”, " Lysitermus pallidus Furst ", " Fam. 3 Hecaboloidae , n. gen. (rest illegible)" ; 4 ♀ + 1 ♂ (RMNH), " Sweden: Skåne, Fjälkestad, Balsberget, ex cases of Diplodoma laichartingella ( Goeze ) ( Psychidae ), coll. 25.vi.2019, em. (indoors) 18.ii.2020, F. Skeppstedt " ; 1 ♀ (NMS), " Finland: Lemland, Flaka, Björkö, 59.98°N, 20.19°E AI, 3.viii.2004, ex?Psychid [= Diplodoma laichartingella ] case, N. R. Fritzen ", " ♀ Ant 17, Lysitermus pallidus Foerster, det. M. R. Shaw 2015" .

Redescription.

Figured and reared ♀ from Sweden (RMNH), length of body 2.2 mm, and of fore wing 1.6 mm.

Head. Antenna 1.2 × as long as fore wing, with 16 segments, slightly widened apically (Fig. 1 ), scapus oblique apically, length of third segment 1.3 × fourth segment; third, fourth and penultimate segments 5.0, 4.0, and 2.4 × their width, respectively; face largely smooth, with long erect setae and 1.7 × wider than high; clypeus smooth, upper half distinctly convex and ventral half depressed; head in dorsal view 1.8 × broader than long medially, eye 1.3 × longer than temple dorsally, strongly and roundly narrowed posteriorly (Fig. 7 ); vertex finely granulate and superficially rugulose near stemmaticum (Fig. 8 ); occipital carina strong and in front of it crenulate; POL: diameter of posterior ocellus: OOL = 4:2:6; eye in lateral view 1.6 × as high as wide, temple distinctly broadening ventrally and width of eye 1.2 × minimum width of temple (Fig. 1 ); malar space 0.7 × as long as height of eye and 1.3 × as long as basal width of mandible; frons smooth, except for some fine rugulae.

Mesosoma. Mesosoma 1.4 × as long as high in lateral view; mesoscutum granulate and with rather long, narrow, medio-posterior groove (Fig. 3 ); notauli shallow, complete, largely smooth and anteriorly connected to lateral irregular carina; scutellar sulcus with 3 carinae; scutellum finely striate antero-laterally and superficially granu late medially (Fig. 3 ); propodeum granulate and with large areola, its median carina much shorter than anterior side of areola (Fig. 3 ); side of pronotum rugose-crenulate and secondary granulate sculpture; mesopleuron largely smooth and convex (Fig. 1 ); precoxal sulcus rather deep and only anterior half present, with few crenulae; metapleuron densely rugulose and with long setae; mesosternal sulcus deep, narrow and smooth. Wings. Fore wing: pterostigma elongate triangular and 4 × longer than wide (Fig. 2 ), r issued near its middle and 1.2 × longer than width of pterostigma; 2-SR complete and sclerotized left wing) or only basal two-thirds pigmented (right wing, Fig. 2 ); 3-SR 1.6 × longer than r; SR1 straight and reaching tip of wing; m-cu distinctly postfurcal, rather short (Fig. 2 ); subdiscal cell distally closed, CU1b close to m-cu and CU1a at same level as 2-CU1 (Figs 1 , 2 ). Legs. Hind coxa largely smooth; length of femur, tibia and basitarsus of hind leg 5.5, 11.4, and 10.2 × their width, respectively; hind tarsus compressed.

Metasoma. Length of first tergite 0.6 × its apical width, its surface longitudinally striate and with additional granulate sculpture between striae, dorsal surface evenly convex, its dorsal carinae lamelliform and medially interconnected; medial length of second tergite 0.9 × its basal width, and 1.4 × as long as third tergite; second and third tergites longitudinally striate (but on middle of third tergite weakly developed) and secondary granulate sculpture; second transverse suture coarsely crenulate and nearly straight (Fig. 4 ); third tergite antero-laterally without minute, tooth-shaped protuberance and distinctly narrowed posteriorly (Figs 4 , 5 ), with narrow, rugulose, and rather dull apical rim medially (Fig. 5 ) and distinctly serrate latero-apically (Fig. 4 ); apical lamella of third metasomal tergite distinctly protruding laterally (Fig. 1 ), concave and wide in dorsal view, with approx. 25 carinae (Figs 4 , 5 ); setose part of ovipositor sheath 0.23 × as long as fore wing and 0.5 × as long as hind tibia, nearly parallel-sided (Fig. 1 ).

Colour. Yellowish brown; third tergite mainly yellowish brown but laterally darkened, not contrasting with similarly coloured second tergite (Figs 1 , 5 , 26 ); mesosoma brown, but mesoscutum and scutellum largely dark brown; antenna (basal segments yellowish), pterostigma (but basal quarter yellow) and veins M+CU1 apically, 1-CU1, 1-SR, 1-M, r, and veins of apical half of fore wing dark brown (Fig. 2 ); palpi and tarsi pale yellowish; remainder of legs yellowish brown; wing membrane infuscate, but with subhyaline band below base of pterostigma (Fig. 1 ).

Variations. Antenna with 16-17 segments; length of body 2.1-2.3 mm, and of fore wing 1.6-1.7 mm; length of ovipositor sheath 0.21-0.23 × as long as fore wing; vein 2-SR of fore wing varies in reared series from nearly complete to entirely absent (Fig. 2 ), most frequently only basal half present as pigmented but unsclerotised vein; notauli complete to posterior third obsolescent; second metasomal tergite 1.3-1.5 × longer than second tergite; lamella of third tergite more or less serrate (Figs 1 , 5 ).

Male. Very similar to female, but metasoma slenderer (Fig. 11 ); head dark brown dorsally; third tergite more or less darkened in ♂ (Fig. 9 ), striate and/or granulate and its lamella serrate and with approx. 20 carinae (Figs 9-11 ); pterostigma dark brown basally.

Distribution.

Finland, Germany, Moldova, *Sweden.

Biology.

Five specimens of Lysitermus pallidus hatched from ten final instar larval cases of Diplodoma laichartingella (Goeze, 1783) ( Lepidoptera , Psychidae ) collected in Sweden by the second author. Dissection of the final instar larval cases showed that only three had been parasitized and five specimens had hatched from them. It clearly indicates that L. pallidus is a gregarious larval ectoparasitoid of this host, but probably a facultative one perhaps depending on the size (first- or second-year stage?) of the host. In northern Europe D. laichartingella has a two-year life cycle which raises the question of whether L. pallidus is a parasitoid only of fully grown larva and, therefore, has a two-year lifecycle like its host ( Kunz 1989) or whether it might be able to complete its lifecycle in a juvenile larval case as well. The D. laichartingella cases are usually found in woodland areas where the caterpillar feeds on algae/mosses as well as dead insects on tree trunks, especially, of Fagus sylvatica L. and Quercus robur L. The specimen from Finland has also been reared from D. laichartingella (det. M. Mutanen) but was referred by Gupta and Quicke (2018) as reared from an unidentified psychid host.

Figures

Figure 1. Lysitermus pallidus Foerster, ♀, Sweden, habitus lateral. Photograph: R. Soethof.

Figures 2 - 8. Lysitermus pallidus Foerster, ♀, Sweden 2 wings 3 mesosoma dorsal 4 metasoma dorsal 5 second and third metasomal tergites dorsal 6 head anterior 7 head dorsal 8 detail vertex dorsal. Photographs: R. Soethof.

Figures 9 - 11. Lysitermus pallidus Foerster, ♂, Sweden 9 habitus lateral 10 third metasomal tergite dorsal 11 propodeum and metasoma dorsal. Photographs: R. Soethof.

Figures 26 - 27. 26 Lysitermus pallidus Foerster, ♀, Sweden (freshly emerged specimen), habitus lateral 27 L. tritoma (Boucek), dark ♀, Finland, metasoma dorsal. Photographs: F. Skeppstedt (26) and P. Malinen (27).