Calixomeria, a new genus of Sceliotrachelinae (Hymenoptera, Platygastridae) from Australia

Abstract Calixomerialasalleigen. n. et sp. n. is described as a new genus and species of Sceliotrachelinae. Calixomeria most closely resembles genera of the Aphanomerus-cluster but possesses several characters that readily separate it from other sceliotracheline genera. The key of Masner and Huggert (1989) is modified to accommodate Calixomeria, and the relationship of the genus to other members of the subfamily is discussed.


Introduction
Platygastroidea is well represented in Australia. Approximately 10% (740 species in 80 genera) of all described species occur there, with an estimated 1800 species left to be described (ABRS 2015). A disproportionate amount of that diversity, however, has been described in the family Scelionidae, one of two families that classically comprise the superfamily Platygastroidea (Talamas and Buffington 2015). Much less attention has been paid to Platygastridae, and even less to the subfamily Sceliotrachelinae, due to their small size (most species < 1 mm) and rarity in collections (Masner and Huggert 1989).
The first Australian sceliotrachelines were described by Robert C. L. Perkins during his search for natural enemies of leafhoppers as an entomologist with the Hawaiian Sugar Planters' Association (Perkins 1905). Shortly thereafter, Alan P. Dodd, then an assistant entomologist with the Bureau of Sugar Experiment Stations, added two genera, Aphanomerella Dodd and Platygastoides Dodd (Dodd 1913a, b). Following Dodd, descriptions of Australian sceliotrachelines all but stopped until the landmark work of Masner and Huggert (1989), who erected 13 new genera, including several known only from Australasia. The purpose of our research is to follow in the footsteps of Perkins and Dodd by describing an unusual new genus of Sceliotrachelinae from southern Australia.
The contributions of the authors are as follows: Z. Lahey: character definition and coding, generic concept development, species concept development, imaging, key development, manuscript preparation; L. Masner and N. F. Johnson: character definition, generic concept development, species concept development.

Materials and methods
The numbers prefixed with "OSUC" or "USNMENT" are unique identifiers for the individual specimens (note the blank space after some acronyms). Details of the data associated with these specimens may be accessed at the following link: https://hol.osu. edu, and entering the identifier in the form.
Images were captured with a Leica MC170 HD digital camera attached to a Leica Z16 APOA microscope using Leica Application Suite (version 4.12.0), or with a Canon EOS 70D attached to an Olympus BX51. Image stacks were combined into a single montage image using Zerene Stacker (version 1.04). Montage images were postprocessed with Adobe Photoshop CS6 Extended and are archived at https://specimage. osu.edu, the image database at The Ohio State University.
Scanning electron micrographs were produced with a Thermo Fisher Scientific Apreo Scanning Electron Microscope. The specimen was disarticulated with a minuten probe on a 0.5-inch slotted aluminum mounting stub using carbon adhesive tabs. The specimen was not coated.

Collections
This work is based on specimens deposited in the following repositories:
Mesosoma. Color of mesosoma: light to dark brown. Epomium: absent. Lateral pronotal area: strongly excavate below anterior margin of pronotal shoulders. Form of pronotal cervical sulcus: indicated as narrow groove dorsally. Setation of pronotal cervical sulcus: absent. Sculpture of pronotal shoulders: imbricate. Pronotal shoulders: visible in dorsal view. Anterior margin of mesoscutum: not reflexed, on same plane as posterior margin of pronotum. Sculpture of mesoscutum: imbricate. Shape of mesoscutum: pentagonal, curved along anterior margin. Anterior admedian line: absent.  Diagnosis. Calixomeria possesses several autapomorphic characters that readily separate it from the rest of Sceliotrachelinae, the most salient of which are: LOL and OOL equal in length; knob of submarginal vein with a single, long, spine-like seta; the well-defined paracoxal sulcus; the large mesoscutellum, the posterior margin of which overhangs the metascutellum and most of the propodeum; and the presence of long, stout setae on tergites T2-T6.
In the key to world genera of Sceliotrachelinae (Masner and Huggert 1989), Calixomeria keys to couplet 31 separating Helava from Alfredella Masner & Huggert and Aphanomerus based on the pilosity of T1 and T2, and the presence or absence of foamy structures and median keels on the propodeum. Calixomeria lacks both setae that medially obscure the junction of T1 and T2 and foamy structures on the propodeum, thereby distinguishing it from Helava. Additionally, the propodeum is flat and lacks keels or protuberances, reliably separating Calixomeria from both Alfredella and Aphanomerus.
The key of Masner and Huggert (1989) is modified to accommodate Calixomeria:
Clavomeres are defined by the presence of papillary sensilla on the ventral surface of antennomeres of female platygastroids (Bin 1981). The apical four antennomeres (A7- A10) of Calixomeria females are enlarged, and A7 is fused to A8; however, A7 lacks papillary sensilla (Fig 6). The only sceliotracheline hypothesized to have lost papillary sensilla on one or more of its antennomeres is Pseudaphanomerus, but in this genus sutures between the clavomeres are absent, resulting in a 1-merous clava with a claval formula of 3, presumably from the loss of papillary sensilla on A7 and A8 (Masner and Huggert 1989). Aleyroctonus Masner & Huggert may be another example of this reductive trend: its claval formula is 1-2-2 and A7 is enlarged relative to A6; however, A7 is clearly separated from the clava by a deep suture, which is faintly indicated in Calixomeria.
The elongate marginal cilia of the fore wing are found in relatively few taxa within Platygastroidea (e.g., Dyscritobaeus Perkins, Embioctonus Masner, Encyrtoscelio Dodd, Eumicrosoma Gahan, Exon Masner, Idris Förster). Sceliotrachelines that possess this character are Errolium Masner & Huggert and Neobia Masner & Huggert, but in these genera the apex of the submarginal vein nearly touches the anterior margin of the fore wing, whereas it is distant from the margin in Calixomeria (Fig. 3). In addition, there is a single, long, spine-like seta near the anterodorsal margin of the knob of the submarginal vein in Calixomeria, a character not known to us elsewhere in Platygastroidea.
Calixomeria is most easily recognized by its cup-shaped mesoscutellum that overhangs the metascutellum and most of the propodeum (Figs 1, 3, 4, 13). This character is not encountered elsewhere within Sceliotracheline, but is expressed to varying degrees in certain scelionids, some of which possess a mesoscutellum very similar in appearance to Calixomeria (e.g. Gryon Haliday). Convergence in the character systems mentioned above may reflect biological (i.e., host choice) or environmental (i.e., habitat) similarities between these genera. Unfortunately, host associations are known for just a fraction of the superfamily. Molecular data from additional, freshly collected specimens would greatly facilitate the placement of this taxon within the framework of Sceliotrachelinae.