Spilichneumon THOMSON, 1894

A. M, 2011, Illustrated key to the genera of the subtribe Amblytelina of Palaearctic (Hymenoptera, Ichneumonidae, Ichneumoninae, Ichneumonini), Linzer biologische Beiträge 43 (1), pp. 597-711 : 646-649

7. Spilichneumon THOMSON

Spilichneumon THOMSON 1894 - Opusc. Ent. fasc. 19: 2087.

Type species: Ichneumon occisor FABRICIUS.

Spilichneumon: HEINRICH 1961 - Can. Ent., Suppl. 18: 180-182.

Spilichneumon: HEINRICH 1965 - Entomol. Ts. Agr. 86, 1-2: 91-92.

Spilichneumon: HEINRICH 1977 - Ichn. Florida and Neigb. States 9: 109-110.

Spilichneumon: RASNITSYN 1981 - Opr. Faun. SSSR 3 (3): 568, 621-622.

D i s t r i b u t i o n: Holarctic, Oriental Region.

I n t r o d u c t i o n:

Genus Spilichneumon can be identified by combination of two decisive characters peculiar to the males: hypopygium tapering into a more or less prolonged and usually apically pointed median process and flagellum with very long row of elongate, bacilliform tyloides beginning from the 2nd, 3rd, or 4th segments.

Considerable sexual dimorphism is characteristic to the representatives of the genus. In this connection the diagnosis of genus is of compromise character. When intermediate forms are present, it becomes necessity to involve associated males or females in the analysis of generic belonging.

The presence of long process of hypopygium of males, make it possible to distinguish easily the representatives of genus from males of Ichneumon LINNAEUS and from another genera of Ichneumonina subtribe.

As by males and also by females, Spilichneumon is distinguished from Diphyus KRIECHBAUMER by more or less distinct thyridia. However, in species with slightly impressed gastrocoeli this character looses its significance, first of all in females.

For females of the genus, more flattened thorax, a tendency to elongation of abdomen, more stout flagellum, absence of a bunch of bristles at apex of hypopygium are characteristic. These characters make it possible to distinguish females of the genus from females of Eutanyacra CAMERON with more shortened propodeum, compressed from sides apex of abdomen and with a bunch of stiff bristles at apex of hypopygium and with more slender flagellum. In contrast to Diphyus KRIECHBAUMER females of the genus have more distinct thyridia, more strong mandibles, more strong legs and flagellum and more elongated propodeum.

Species of the genus with strong, swollen mandibles have characters similar to that of Bureschias HEINRICH. There are morphology of mandibles, angle-shaped profile of a head from side, impressed clypeus and other characters, connecting with parasitizing on cryptophagous larvae of Noctuidae .

Males are distinguished from males of Eutanyacra CAMERON by more longer (longer than width) area superomedia, from Diphyus KRIECHBAUMER by long median process of hypopygium along with usually distinct thyridia.

M o r p h o l o g y:

F l a g e l l u m: Of female always bristle-shaped, usually stout with shortened and sharply differentiated segments. Flagellum of males with closely merged segments (slightly differentiated) and long row of bacilliform tyloides from segment 2(3,4).

H e a d: More or less strengthened (stout); genae and temples behind eyes never strongly narrowed. Mandibles of females bidentate, from normal ( celenae PERKINS ) to strong, frequently swollen at central part with tendency to blunting and shortening of teeth; mandibles of males normal, narrowed to apex or on the larger part parallel-sided, upper tooth longer than lower one.

T h o r a x: Of females with tendency to flattening and elongation; axillary tongue weak, but expressed; scutellum flat, not carinated; scutellum of males more convex in profile. Hind margin of metanotum with projections. Horizontal part of propodeum usually longer or, at least, only just shorter than declivous one; area superomedia frequently considerably longer than width to square ( limnophilus THOMSON ), nothing considerably wider than length; hind parts of areae dentiparae roundly descending backwards, without apophysises and teeth at apices; spiracles long, slit-shaped.

L e g s: Usually stout. Hind coxae of females without scopa.

W i n g s: Areolet, pentagonal, usually with wide base, rarely ( limnophilus THOMSON ) with narrow one; nervulus usually postfurcal.

A b d o m e n:Amblypygous, from above longish-oval or even elongated. Middle field of postpetiolus longitudinally striated; middle field of females slightly marked, of males distinctly elevated. Gastrocoeli rather small and shallow, not transverse, sometimes rudimentary; thyridia distinct with exception of species with rudimentary gastrocoeli; sculpture of second and third tergites considerably fine, apical tergites of typical species smooth and more or less glossy. Only sternites 2-3 of females and more often 2-4 of males with fold. Hypopygium of males tapering into median process, of females without bunch of long stiff bristles at middle of apical part, but sometimes with scattered bristles.

C o l o r a t i o n: Main color of females abdomen black with red. Apical tergites of abdomen black, usually with white pattern, or apical stripes as in occisor F. and limnophilus THOMSON , or apical white spots, as at ammonius GRAVENHORST and celenae PERKINS. Sexual dichroism strongly developed and analogous to that of the genus Ichneumon LINNAEUS. Abdomen of males frequently red with black, rarely yellow with black apex and yellow apical pattern (e.g. occisor).

S i z e: Palaearctic species 10-18 mm.

B i o l o g y a n d e c o l o g y:

H o s t s: 9 species of Noctuidae are known as the hosts of 5 West Palaearctic species of a genus from the literature: S. occisor (F.) – Cirrhia togata ESP., Gortyna flavago DEN. et SCHIFF. , S. ammonius (GRAV.) – Gortyna flavago DEN. et SCHIFF. , S. limnophilus (THOMS.) – Archanara algae ESP. , Archanara sparganii ESP., Cirrhia togata ESP., Gortyna flavago DEN. et SCHIFF. , Nonagria geminipuncta Haworth , N. typhae THUNBERG , S. johansoni (HOLMGR.) – Archanara sparganii ESP. , Gortyna flavago DEN. et SCHIFF. , Eurois occulta L., Nonagria cannae OCHSENHEIMER, N. typhae THUNBERG , S. celenae PERK. – Celaena haworthii CURTIS ( HERTING 1976; RASNITSYN 1981).

Species composition, abundance and biotopical d i s t r i b u t i o n: Genus Spilichneumon is presented in region of researches by 5 species. Abundance of this genus in the nature (quantity of the collected individuals / quantity of revealed species of a genus) leads it to the 3rd place according to indicator of abundance among Amblytelina and on 20th place among genera of Ichneumoninae St. in the region (41,8 individuals / 1 species of genus). According to abundance in collections in decreasing order they are distributed as follows: S. celenae PERK. – 74,5 %, S. ammonius (GRAV.) – 10,1 %, S. johansoni (HOLMGR.) – 9,1 %, S. limnophilus (THOMS.) – 4,3 % and S. occisor (F.) – 1,9 %.

The overwhelming quantity of representatives of the genus (99,5 %) falls on the forest ecosystems, first of all pine forests. The greatest abundance of species of the genus is characteristic for raised bogs. It is caused by fact, that the most mass species of the genus in collectings, S. celenae PERK. , also inhabits in the raised bogs, typical biotopes of its host Celaena haworthii CURTIS. (BOND &GITTINGS 2008) . Moreover, the greatest quantity of collectings during all period of investigations also was conducted in these ecosistems. In other ecosystems, this species is marked by separate specimens, and only in the biogeocenoses adjoining to the raised bogs. Another numerous species in collections – S. ammonius (GRAV.) has been registered mainly on raised bogs too. Its abundance, however, was in nine times more low than abundance of S. celenae . Abundance of S. johansoni (HOLMGR.) in collections corresponds to abundance of S. ammonius , but it was met mainly in pine forests (Pinetum pleuroziosum). S. limnophilus (THOMS.) is registered in open ecosystems and on raised bogs (Pinetum sphagnosum). The most rare species in collections – S. occisor (F.) is registered by separate specimens in the wood sorrel spruce forests (Alnetum urticosum). Practically in all species in collections, females dominated. In the most mass species, collected by mainly standard methods, the ratio of females: males was in S. celenae – 2,4:1, in S. ammonius – 6:1.

S e a s o n a l a c t i v i t y a n d h i b e r n a t i o n: Females of representatives of the genus hibernate as adult (HEINRICH 1961, RASNITSYN 1981). A. RASNITSYN (1964) adduces two species, hibernating on imaginal stage – S. ammonius (GRAV.) and S. occisor (F.). Despite on efforts during many years, we did not find females at the stage of hibernation. It is most possibly connected with low abundance of representatives of a genus. Collections of females of the genus in winter season on raised bogs, where they were most numerous were not carried out. By activity of two most mass species that collected with use of Malaise traps, it is possible to see that females appear already in May the first. The maximal activity of females S. celena is observed in July, and S. ammonius – in June. The maximal activity of males of these species is observed with a time delay of 1-2 months. Most probably, species of this genus are being developed in one generation.