Astromesitius, a new genus of Mesitiinae (Hymenoptera, Bethylidae) from the Old World

Literature about Mesitiinae Kieffer, 1914 has not been treated extensively from a taxonomic viewpoint in comparison with other subfamilies in Bethylidae Latreille, 1802. Our research on species of Metrionotus Móczár, 1970, Clytrovorus Nagy, 1972 and Sulcomesitius Móczár, 1970 revealed a new hypopygium shape pattern, namely a ‘star-shaped’ hypopygium, which is characteristic of a new genus, Astromesitius gen. nov., with two new species Astromesitius thionyi gen. et sp. nov. and Astromesitius olavoi gen. et sp. nov. The descriptions of both new species are based on male specimens collected in Thailand and the United Arab Emirates. Astromesitius quatei (Móczár, 1977) gen. et comb. nov. is designated as type species for the new genus, which is erected for a total of seven species. The main diagnostic characteristics are the head longer than wide; a clypeus with a median lobe quadrate; an antenna with distinct long setae, with pedicel caliciform, and with flagellomeres long and caliciform; pronotum and anteromesoscutum with longitudinal sulcus indistinct or absent; metapectal-propodeal complex with posterior projection hardly distinct or absent; hypopygium star-shaped; genitalia with aedeagus slender and fusiform.


Repositories
The names of collection managers are given in brackets. The terms applied to the body structures follow Azevedo et al. (2018); those related to the integument follow Harris (1979).

HE
= length of the eye in lateral view LFW = length of the forewing LH = length of the head including clypeus in dorsal view VOL = vertex-ocular line in dorsal view The descriptions and key were elaborated with DELTA (Descriptive Language for Taxonomy) according to Dallwitz et al. (1993). The genera of Mesitiinae were identifi ed using the key proposed by Azevedo et al. (2018).
The illustrations were obtained using Leica MZ80 stereo microscope. Images were obtained using Leica MD2500 microscope magnifying glass attached to a Leica DFC 495 video camera; the program Leica LAS (Leica Application Suite ver. 3.6.0; Microsystems by Leica (Switzerland) Limited) was used to capture individual images under the Scalable and Modular Dome Illumination System by Kawada & Buffi ngton (2016). Images were combined using Helicon Focus software (ver. 4.2.9); render method was based on Method C (Pyramid). All illustrations and plates were produced in software for image editing and vectorization using adjustments (e.g., levels, shadows / highlights), tools (e.g., healing brush, clone stamp) and fi lters (e.g., unsharp mask).
WINGS. Fore wing with Rs&M vein arched; pterostigma short, about as long as prestigmal abscissa of R1, distal margin convex. Hindwing with three distal hamuli, fi rst hamulus widely separated from others.
METASOMA. Mostly polished, tergum I mostly glabrous, subsequent terga progressively more setose laterally and posteriorly. Hypopygium as long as wide; anterior stalk wide and long; lateral projection long; posterior margin with branches short and wide ( Fig. 2A). GENITALIA (Fig. 3A). Paramere apex sparsely setose; ventral arm of paramere club-shaped, wide at apex; dorsal arm shorter than ventral arm, club-shaped, and with basal margin thin. Cuspis ventral arm not reaching dorsal arm apex, wide; dorsal arm wide. Aedeagus slender, with apex aligned with paramere apex, apical margin truncate, lateral margin of basal portion convex. Apodeme parallel, base curved laterad.

Remarks
This species is similar to Astromesitius carbonarius (Móczár, 1970) and A. minutissimus (Móczár, 1971), mainly in having the small and black body; the head longer than wide; the hyaline forewing. Astromesitius olavoi gen. et sp. nov. can be distinguished from these two species by having the frons, the dorsal pronotal area and the mesopleuron sparsely foveolate; the dorsal pronotal area with longitudinal sulcus, but inconspicuous; the metapectal-propodeal disc with posterior projection inconspicuous; the genitalia with truncate and projected apex of aedeagus. Thus we did not doubt the validity of a new species.

Distribution
Thailand.

Diagnosis
Head as long as wide. Malar space shorter than VOL, parallel. First fl agellomere as long as pedicel.

Material examined
WINGS. Forewing with Rs&M vein arched; pterostigma short, about as long as prestigmal abscissa of R1, distal margin convex. Hindwing with three distal hamuli, fi rst hamulus widely separated from others.
METASOMA. Mostly polished, tergum I mostly glabrous, subsequent terga progressively more setose laterally and posteriorly. Hypopygium as long as wide; anterior stalk wide and long; lateral projection short; posterior margin with branches short and slender (Fig. 2B).

Remarks
The species Astromesitius thionyi gen. et sp. nov. is slightly similar to A. indistintus, with which it shares the absence of a longitudinal ridge between the metapostnotal median carina and metapostnotalpropodeal suture. The new species is distinguished from all the other species of Astromesitius gen. nov. by the coriaceous body surface; the polished metapostnotal-propodeal complex surface; the metapostnotal median carina incomplete; the coriaceous propodeal declivity and lateral surface of the metapostnotalpropodeal complex; the genitalia with sinuous paramere ventral arm. Astromesitius thionyi gen. et sp. nov. is the smallest species of the genus and the characteristics cited above are exclusive to this species among Astromesitius gen. nov. species; thus we did not doubt the validity of a new species.

Remarks
This species was originally described in Metrionotus (Móczár 1970a) from South Africa (Móczár 1970a), and was later recorded from the United Arab Emirates (Barbosa & Azevedo 2011). We examined one male from UAE deposited at UFES, and the analyses reveal that their characteristics correspond to Astromesitius gen. nov. Thus, we propose a new combination for this species from Metrionotus to Astromesitius gen. nov. (Barbosa & Azevedo, 2011)

Remarks
This species was originally described in Metrionotus (Móczár 1970a) from the United Arab Emirates (Barbosa & Azevedo 2011). We examined one male type, the paratype, from material deposited at UFES, and the analyses reveal that its characteristics perfectly fi t Astromesitius gen. nov., including the star-shaped hypopygium. Thus, we propose a new combination for this species from Metrionotus to Astromesitius gen. nov. (Móczár, 1971)  Metapectal-propodeal complex as long as metapectal-propodeal complex half-width, without longitudinal ridge between metaposnotal median carina and metaposnotal-propodeal suture; metaposnotal surface areolate; posterior spine of metapectal-propodeal complex absent. Propodeal declivity striate. Lateral surface of metapectal-propodeal complex areolate. Metasoma with hypopygium longer than wide; anterior stalk wide and short; posterior margin with branches short and wide. Genitalia with paramere apex sparsely hairy; aedeagus slender, with apex surpassing paramere apex, apical margin rounded, lateral margin of basal portion slightly convex.

Male
Hypopygium longer than wide; anterior stalk slender and long; posterior margin with branches short and wide. Genitalia with paramere apex sparsely hairy; ventral arm of paramere sinuous and slender; aedeagus slender, with apex aligned with paramere apex, apical margin rounded, and with short outer projection, lateral margin of basal portion slightly convex.

Remarks
This species was originally described in Sclerodermus (Costa 1864) based on one female from Italy. It was transferred to Mesitius by Kieffer (1914), who synonymised Sclerodermus mutilloides under Mesitius ghilianii Spinola, 1851. Argaman (2003 revalidated the status as a valid species and transferred this species from Mesitius to Clytrovorus. Argaman also established the synonymy of Mesitius fuscicornis Kieffer,1906, M. zavadili Hoffer, 1936and M. viator Nagy, 1968 under this species. We did not have access either to the type, which is lost, or to any other voucher specimens of this species, and the original descriptions are not sufficiently detailed to compare with the diagnostic characteristics of Astromesitius gen. nov. However, the illustration by Argaman (2003) is clear and suffi cient to analyze and reallocate this species from Clytrovorus to Astromesitius gen. nov., because it has long and sparse antennal pubescence and the hypopygium is 'star-shaped'.

Remarks
This species was originally described in Sulcomesitius and recorded from Vietnam (Móczár 1977). We examined the holotype male deposited at BPBM, and the analyses reveal that it fi ts the concept of Astromesitius gen. nov., mainly because of the hypopygium shape. Thus, we propose a new combination for this species from Sulcomesitius to Astromesitius gen. nov.

Discussion
Since the Mesitiinae synopsis by Argaman (2003), the hypopygium has played a very important taxonomic role at a genus level within the subfamily. Argaman postulated that each genus has a conservative hypopygium morphology, with very little variation within each one, but with huge morphological distinctions among the genera.
Five species of Metrionotus, Clytrovorus and Sulcomesitius (see 'Included species' above) were recognised as possessing a 'star-shaped' hypopygium. The 'star-shaped' hypopygium has as its main characteristic the latero-anterior arm developed, and this development could be associated with the muscle insertion. Schulmeister (2003) recognised the lateral S9-cupulal muscle; this muscle originates from the gonocondyle in the cupula of the genitalia and inserts laterally on the ninth sternite (hypopygium). The cupula is attached to the base of male genitalia, and the muscles between the cupula and the hypopygium enable some movements of genitalia structures. Thus, the lateral S9-cupulal muscle exerts direct action on the male genitalia. According to Boudinot (2013) this muscle torques the genitalia by the elevation of the cupula basal margin; probably the greater insertion point could increase the torque movement. Thus, the long latero-anterior arms of the 'star-shaped' hypopygium might give an additional functional advantage during copulation in comparison to the other genera of Mesitiinae. It could ensure a better muscle insertion and improve the muscle action of male genitalia movement. Moreover, this distinct shape of hypopygium makes Astromesitius gen. nov. easy to recognise among the other genera of Mesitiinae.
There are some other important characteristics to diagnose the genus. One of them is the surface sculpture of the integument. Most Mesitiinae have the integument surface densely impressed with large foveae and with a longitudinal median sulcus on the mesosoma, characteristics that could be an evolutionary novelty for this subfamily. Astromesitius gen. nov., however, has the body sparsely foveolate or almost not foveolate and the longitudinal median sulcus hardly distinct or absent. The genera Anaylax Móczár, 1970, Bradepyris Kieffer, 1905, Clytrovorus and Moczariella Barbosa & Azevedo, 2014-see Móczár (1970b, Barbosa & Azevedo (2014), Nagy (1972) and Barbosa & Azevedo (2014), respectively -have the integument with weak sculpture and without a longitudinal sulcus crossing the dorsal mesosomal area, or when present it is hardly distinct. In Mesitiinae, the more foveolate integument is related to a more conspicuous longitudinal sulcus of the mesosoma and a larger posterior projection of the metapectal-propodeal complex (see details in Azevedo et al. 2018).
The antennal pubescence in Mesitiinae can be short, medium or long, thick or thin, and dense or sparse (Argaman 2003;Móczár 1970a, b). However, in most genera the antennal pubescence is short, only in Incertosulcus Móczár, 1970 and Astromesitius gen. nov. the antennal pubescence is medium or long. Thus, although this condition is not exclusive to Astromesitius gen. nov., it helps conceptualise the genus. As emphasised by Riolo et al. (2016), antennal pubescence and sensilla play an important role in perception, therewith, this pubescence length could give additional adaptation fi tness to Astromesitius gen. nov. species, thus becoming diagnostic for this genus.