‘The adikeshavus-group’: A new species group of Idris Förster (Hymenoptera, Platygastridae) from India, with descriptions of five new species

Idris Förster is a megagenus in the tribe Baeini comprising species that exclusively parasitize the eggs of spiders dwelling in vegetation and leaf litter. This is the only tribe in Platygastridae capable of using spider eggs for their development. Constructing species groups will facilitate studies of highly speciose genera like Idris. So far only one species group ‘the melleus-group’ has been proposed in this genus. A new species group ‘the adikeshavus-group’ from India is proposed. Five new species in this genus – I. adikeshavus, I. deergakombus, I. brevicornis, I. lopamudra and I. teestai – are described from India. All five species are imaged and a key to them is provided.


Introduction
Platygastroidea, the third largest superfamily of Parasitic Hymenoptera, are ubiquitous. They parasitize the eggs of most orders of insects and are host group specific. For instance, Gryonini use heteropteran eggs, Teleasinae and Xenomerini use carabid eggs, Embidobiini use embiid eggs, and so on (Masner 1976;Austin et al. 2005, Austin andField 1997). The tribe Baeini under subfamily Scelioninae (one of the five subfamilies in Platygastridae) is worldwide in distribution. All species in Baeini are known to be specialist parasitoids on the eggs of spiders (Austin 1985, Austin andField 1997). This high level of host specificity is the result of their having speciated along with spiders over an extended period of time Austin 2000a, Stevens and. They also exhibit high levels of sexual dimorphism that varies be-The genus Idris (Tribe: Baeini) was erected by Förster in 1856 with I. flavicornis as the type species (Förster 1856). Masner and Denis (1996) state that very small or very large eggs of spiders are not parasitized by this genus, as a result of which all species are generally of uniform size varying from 1-2 mm. So far 154 species of Idris have been described worldwide (Johnson 2015), of which 24 are from India (Mani 1939(Mani , 1973(Mani , 1975Mani and Mukerjee 1976, Mani and Sharma 1982, Mukerjee 1978, 1981, 1994. Idris and Ceratobaeus were considered two distinct genera by Masner (1976). Later Huggert (1979) treated Ceratobaeus as a subgenus of Idris. Austin (1984Austin ( , 1995 and Galloway and Austin (1984) retained them as two separate genera. In 1996 Masner and Denis in their work on the 'melleus-group' of Idris treated Ceratobaeus as a junior synonym of Idris. Iqbal and Austin (2000a) state that both Ceratobaeus and Idris are polyphyletic and were of the opinion that they be treated as distinct till the Baeini as a whole are studied to resolve the confusion. This was later resolved by molecular studies conducted by Carey et al. (2006) and Murphy et al. (2007) based on combined analysis of the nuclear 28s rRNA and mitochondrial CO1 genes both of which indicated that Baeini is not monophyletic. Three definitive clades were found viz. clade A consisting of Idris + Ceratobaeus Ashmead + Hickmanella Austin + Odontacolus Kieffer; clade B with Baeus and clade C with Mirobaeoides Dodd + Neobaeus Austin. Mirobaeoides and Neobaeus were more closely related to other platygastrids that do not parasitize spider eggs. Analysis of highly species rich genera like Idris and Ceratobaeus indicated that they were not monophyletic and that the horn on T1 housing the long ovipositor (when not in use) has evolved many times within the tribe. The reduction in wings was inferred to be an adaptation to enhance the efficiency of locating spider eggs in leaf litter and for penetrating the silk walls of the egg sacs of spiders. It was also concluded that macroptery is most likely an ancestral condition in Scelionidae, with no evidence that this character state had been regained as functional wings post wing reduction. The results of these molecular phylogenetic studies were at odds with the phylogenies constructed using morphological characters alone (Carey et al. 2006, Murphy et al. 2007).
As Idris is highly speciose with the possibility of over a thousand species being present (Valerio et al. 2013), the clustering of species into groups will aid in the study of this genus. Only one species group, the 'melleus-group', has so far been proposed by Masner and Denis (1996) for Nearctic species of Idris. India being a subtropical country will without doubt harbour a large fauna of Baeini. This initial study of Indian species of Idris reveals a closely knit group of five species for which a new species group, 'the adikeshavus-group' has been proposed. The females of the species in this group possess a horn on T1 which is absent in males and the propodeum present as lateral lamellae anterior to the horn. Other diagnostic characters of this species group have been mentioned under results.

Materials and methods
Morphological terminology is after Masner (1976Masner ( , 1980 and Mikó et al. (2007Mikó et al. ( , 2010. Specimens were mounted on point-card tips. The descriptions and imaging were carried out employing Leica M205A stereomicroscope, with 1× objective and Leica DFC-450 digital camera.
The holotypes and paratypes of all the five new species are deposited in the ICAR-National Bureau of Agricultural Insect Resources, Bangalore, India.

̒ The adikeshavus species-group̓
Diagnosis. This species group is very unique as compared to all other Idris spp. in the following combination of character states: 1. T2 is either 1.7-2.0× longer than T3 or equal to T3 2. Both fore wing and hind wing with extremely long marginal cilia; hind wing curved inwards beyond submarginalis 3. Both wing shape and density of microtrichia on wings vary between males and females 4. Presence of propodeum as lateral lamellae anterior to horn 5. T7 and S6 very large and elongate 6. Densely setose vertex 7. Male antenna twelve segmented, constriction between A11 and A12 distinct Description. Body convex; head transverse, wider than mesosoma in dorsal view; eyes small, densely setose; lateral ocelli adjacent to eyes; temples not visible when viewed laterally; head wider than high, higher than long; IOS larger than eye height; vertex with dense setae; facial striae present, striae reaching lower orbit of eye; lower frons smooth, upper frons setigerous punctate; central keel well developed, not reaching anterior ocellus; occipital carina sharp; radicle elongate, > 1/4 th length of A1; female clava broad; length of clava 1.0-1.4× length of A2-A6; male antenna with clear constriction between A11-A12.
Mesosoma: Notauli well developed posteriorly, ranging in length from 0.27-0.32× length of mesoscutum; mesoscutum and mesoscutellum densely setose; mesoscutellum semicircular; metascutellum narrow in females and well defined in males; propodeum present as lateral triangular lamellae; lateral pronotal area rugose or with weak transverse ridges; mesopleuron with or without several transverse ridges beneath tegula; mesopleural depression distinct; metapleuron almost smooth; in females fore wing spatulate and with extremely long marginal cilia 1.7-2.2× width of wing; hind wing with a typical inward curve at the end of submarginal vein; hind wing marginal cilia 2.18-2.9× width of wing; in males the wings are narrow, densely covered with microtrichia, and hind wing less curved beyond the submarginal vein.
Discussion. The character states, ocelli adjacent to eye; female with seven antennomeres and an unsegmented clava; male antenna with 12 antennomeres; skaphion absent; hind wing with complete submarginal vein reaching frenal hooks and presence of horn on T1 (though not found in many species of Idris) (Masner, personal communication) place this group under Idris.
The members of 'the adikeshavus-group' however can be distinguished from other species of Idris by the combined occurrence of seven character states as mentioned under diagnosis. However the presence of three key character states, viz. T2 either 1.7-2.0× longer or equal to T3; T7 and S6 very large and elongate; fore wing and hind wing with extremely long marginal cilia with hind wing curved inwards beyond submarginalis readily distinguishes this species group from other species of Idris. As of now 'the adikeshavus-group' is restricted to India with five species. Since all species in the Baeini are parasitoids of spider eggs, members of 'the adikeshavus-group' too in all likelihood parasitize the eggs of spiders. The members of this group are rare as only 52 specimens were collected during six years of intensive collecting.
The males and females are sexually dimorphic, varying in the presence and absence of horn on T1, shape of wings and density of microtrichia on wings. The presence of a horn (of variable length between species) indicates the presence of a long ovipositor housed within it when not in use as is the case in Odontacolus and Ceratobaeus s.l.
Etymology. The species is named 'brevicornis' referring to the short horn on T1.
Diagnosis. I. brevicornis differs from I. lopamudra in having a short horn, with the latter having a longer horn which is distinctly costate laterally and posteriorly; T2 in I. brevicornis is 1.95× longer than T3 while in I. lopamudra T2 1.7× longer than T3; propodeum is extended as median costate plate in I. brevicornis which is not so in other species of Idris described here.  (Figs 21,  25). Head, mesosoma, horn on T1 dark brown; metasomal tergites T1-T6 paler than mesosoma; T7 yellowish brown; legs same color as metasoma except paler tarsi; antennae brown except dark brown T2 and clava. Body length=0.989 mm.
Diagnosis. I. deergakombus differs from I. brevicornis and I. lopamudra in having long and denser microtrichia on fore wing while in the latter two the wings are almost smooth; horn on T1 is longer and smooth in I. deergakombus while it is costate in I. brevicornis and I. lopamudra. I. deergakombus has a long horn while it is short in I. brevicornis; In I. deergakombus T2 2× length of T3 while in I. lopamudra T2 1.7× length of T3. Type locality. INDIA, Karnataka, Tamil Nadu Description of female. Color and size (Fig. 28). Head, mesosoma brown, metasoma paler than mesosoma; posterior tergites yellowish brown; legs same color as metasoma; antennae brown to dark brown with patches of yellow on apical A1, anterior and posterior margin of A2 and lateral clava. Body length=0.725 mm.
Male. Not known. Etymology. The species is named 'teestai' after the river Teesta in the state of Sikkim, from where the type specimen was collected.
Diagnosis. This species can be easily distinguished from the other four species described here by reticulate sculpture on mesoscutum and mesoscutellum.