Omphale Haliday

Hansson, Christer & Shevtsova, Ekaterina, 2012, Revision of the European species of Omphale Haliday (Hymenoptera, Chalcidoidea, Eulophidae), ZooKeys 232, pp. 1-157 : 4-6

Omphale Haliday

Omphale Haliday, 1833:339. Type species: Omphale salicis Haliday, by monotypy.

Smaragdites Haliday, 1833:419. Type species: S. admirabilis Haliday, by monotypy. Synonymy by Graham 1963:240.

Secodes Förster, 1856:78, 81. Type species: Secodes fagi Förster, by monotypy. Synonymy by Graham 1963:240.

Holcopelte Förster, 1856:78. Type species: Elachistus obscurus Förster, 1841:40, by original designation. Synonymy by Hansson 2004:142.

Euderomyia Girault, 1913:176. Type species: Euderomyia carlylei Girault, by original designation. Synonymy by Bouček 1988:727.

Chrysocharoideus Ashmead, 1904:370. Type species: Chrysocharis thoracicus Ashmead, by original designation. Synonymy by LaSalle and Schauff 1992:12.

Chrysocharomyia Dodd, in Girault 1915:207. Type species: Chrysocharomyia elongata Girault, by original designation. Synonymy by Bouček 1988:727.

Paromphale Girault & Dodd, in Girault 1915:211-212. Type species: Paromphale flavicorpus Girault, by original designation. Synonymy by Bouček 1988:727.

Raphaelonia Girault, 1924:173. Type species: Raphaelonia sulcatiscutum Girault, by monotypy. Synonymy by Bouček 1988:727.

Eugerium Graham, 1959:202. Type species: Cirrospilus isander Walker, by original designation. Synonymy by Hansson 1996b:5.

Exodontomphale Bouček, 1984:65. Type species: Exodontomphale taborskyi Bouček, by original designation. Synonymy by Schauff 1991:61.

Diagnosis.

Clypeus delimited by grooves at least laterally (e.g. Figs 117, 257, 367, 378); sensilla ampullacea (peglike sensilla) asymmetric; pronotum reduced and usually not visible in dorsal view; occiput without median groove or fold between occipital margin and occipital foramen; male genitalia (Figs 478-501): phallobase with enlarged volsellar setae, paramere with one seta at apex, digitus with two spines (very rarely with one or three spines). The species groups used here are based mainly on the appearance of the male genitalia, and most species have specific characters in this structure. However, since the visualisation of this structure involves slide preparations, characters in the male genitalia have been avoided as much as possible in the identification key, but in a few cases, when this is the only way to separate species, they are used.

Identification.

There are no taxonomically or nomenclaturally updated keys to European genera of Eulophidae . The most recent keys are in Graham (1959) and Peck et al. (1964). They are useful for identification by keeping in mind that Holcopelte and Eugerium come out as separate genera in the keys. Another option is to use the key for Nearctic genera of Chalcidoidea ( Schauff et al. 1997), but Holcopelte is treated as a genus separate from Omphale .

Description.

Flagellum with 2-3 small and discoid anelli; five flagellomeres, free or with apical 2-3 flagellomeres more or less fused, occasionally with a distinct club with apical flagellomeres fused and wider than proximal flagellomeres (degree of fusion of apical flagellomeres is in many cases difficult to assess, and varies intraspecifically). Sensilla ampullacea (peglike sensilla) asymmetric, long or short. Ventral sense area of male scape reaching along almost entire length of scape. Males with verticillate or scattered arrangement of setae. Mandibles usually endodont with two large teeth at apex and with one to several smaller teeth above large teeth. A few Nearctic species have exodont mandibles, but this feature has not been found in European species. Cly- peus entirely delimited, quadrangular to semicircular or triangular in shape. Lower clypeal margin usually arcuately protruding, in a few species straight. Lower frons usually with a cross-ridge reaching almost from eye to eye (see Hansson 1996b, fig. 1), cross-ridge is protruding and is not an edge resulting from the collapse of frons above the antennal toruli, cross-ridge missing in some species. Frontal suture between lower and upper frons present. Antennal scrobes either more or less broadly separated and never joining, or joining at or below frontal suture. Surface between antennal scrobes more or less raised to form an interscrobal ridge. Occipital margin rounded off, rarely with an edge or a carina. Without a weak median groove or fold from occipital margin down to occipital foramen.

Pronotum reduced and hardly visible in dorsal view. Mesoscutum usually with weak delimited notauli; midlobe of mesoscutum with two pair of setae, some non-European species either with one pair or without setae. Scutellum usually without grooves but occasionally with a median groove with variable strength and length, always with one pair of setae usually situated in posterior half. Dorsellum short, smooth, convex or flat, occasionally with strong sculpture. Transepimeral sulcus curved or straight. Propodeum usually smooth and shiny, without anteromedian pit or raised carinae, with or without a narrow transverse proximal groove; propodeal callus with two setae; petiolar foramen semicircular to triangular, usually wide to fit the wide petiole. Forewing with a narrow and bare costal cell; speculum open or closed below; radial cell bare or hairy; with or without one hair line from stigmal vein; postmarginal vein 0.2 –2.1× as long as stigmal vein in European species. Legs usually long and slender.

Petiole short and wide, occasionally as long as wide, pale or dark. Gaster usually subsessile; ovate to lanceolate in female. The male genitalia display important characters useful in classification of the species groups, but also in the separation of species.

The species-groups.

Graham (1963) initially divided the European Omphale into four groups with two unplaced species. However, he did so without any motivation and the groups were not diagnosed. The species groups presented here largely follow the groups presented by Graham, but now defined by morphological characters, and due to the addition of species two groups have been added. Characters in the male genitalia are used extensively to group species and to separate these groups. Graham was not aware of such characters and some species have therefore been transferred from their original placement. The European species are here separated into six groups, and with six unplaced species. The unplaced species comprise species that do not fit in any of the species groups, and that do not share features with each other to form species groups on their own.

Biology.

Hosts or host plant/fungi associations are known for 16 of the 37 European species (Table 1), and in all cases gall midges ( Diptera : Cecidomyiidae ) are the target group. Host records from North America ( Hansson 1996b) and Central America ( Hansson 2004) support the findings for European species, i.e. that Omphale species are exclusively parasitoids on gall midges. Dziurzynski (1961) investigated the biology of Omphale lugens in Poland (given as Secodes coactus in the Dziurzynski publication). Omphale lugens is a koinobiont primary endoparasitoid and the female oviposits in the second instar larvae of its gall midge host, Mikiola fagi , which induces galls on the upper surface of leaves of beech ( Fagus sylvatica ). This parasitoid is solitary or gregarious with up to ten individuals per host. If more than one larva is present per host either the same female lays more than one egg per host, or more than one female oviposits in the same host larva. However, because of the high mortality among gregarious larvae eventually only one parasitoid per host larva will complete its development. The parasitoid speeds up the development of its host, indicated by a faster growth rate in parasitized gall midge larvae, as compared to non-parasitized larvae. There does not seem to be additional, abnormal, instars in the host, just an acceleration of growth. The gall midge larva is killed before pupation by the feeding of the last instar parasitoid larva. Omphale lugens has four larval instars and pupates inside the empty larval skin of its host, still remaining inside the gall.

The only other Omphale species for which more detailed biological information is available is Omphale clypealis . This species is an important biological control agent against the brassica pod midge ( Dasineura brassicae ) on rape ( Brassica napus ), and has thus been the subject of biological investigation ( Williams 2003). Similar to Omphale lugens , Omphale clypealis is a koinobiont endoparasitoid. Females oviposit into mature gall midge larvae in their pod gall, and the parasitoid larva is inside the host when it leaves the gall and burrows into the ground for pupation. The pupa is subsequently killed by the parasitoid. The sex ratio for Omphale clypealis is strongly female biased, and Murchie (1996) reared 97-100% females from samples of the brassica pod midge in the U.K. Material from this species that has been available for this investigation, 147 females and three males, suggests the same female bias. This skewed sex ratio indicates that Omphale clypealis is thelytokous, as are possibly some other Omphale species, such as Omphale rubigus where males have never been found, and Omphale theana in which very few males are recorded.

If data from these two species are transferrable, Omphale species are koinobiont endoparasitoids, possibly solitary - at least with only one surviving parasitoid per host. Little is known about the host specificity of Omphale species. However, known host records suggest host specialization because there are no overlap between the species. The host record for Omphale phruron , Dasineura pyri - same host as in Omphale clymene , is possibly based on a misidentification of the parasitoid. The specimens of Omphale phruron from Dasineura pyri have not been available for this investigation and as the species in this group are difficult to identify misidentification cannot be ruled out.

Distribution.

Even though several parts of the World are very poorly investigated or not investigated at all, existing records show that Omphale is a cosmopolitan genus, known from all zoogeographical regions ( Noyes 2012). As can be seen from previous investigations ( Hansson 1996b, 1997, 2004), and this investigation (Figs 502-538), the species have a very large distribution. Many European species are distributed throughout Europe, and the more limited distribution in some species is possibly due to lack of distributional data. Five European species, Omphale acamas , Omphale erginnus , Omphale salicis , Omphale theana , Omphale versicolor , are also found in North America ( Hansson 1996b), and one of these ( Omphale erginnus ) is distributed south to Central America ( Hansson 2004).