Phylogeny and classification of the Orussidae (Insecta: Hymenoptera), a basal parasitic wasp taxon

The Orussidae is a small family of parasitic wasps, comprising 75 species worldwide. It occupies a key position within the Hymenoptera, being the sistergroup of the Apocrita, a taxon containing all other parasitic wasps. In total, 163 morphological characters were scored for 74 species of Orussidae and five outgroup taxa. The dataset was analysed under different weighting schemes. The results do not support a single phylogenetic hypothesis, but most relationships were retrieved in the majority of the cladistic analyses. Earlier attempts at tribal and subfamily classifications of the Orussidae are not corroborated. Enforcing a strictly cladistic classification at these levels would require the recognition of many redundant taxa without enhancing the information content. It is proposed that formal recognition of tribes and subfamilies within the Orussidae be abandoned. The generic concepts of the family are revised. Sixteen genera are recognized; detailed descriptions and illustrations of each are provided, as is a key to the genera. The monophyly of most genera as defined here is well supported, with the exception of Guiglia Benson, 1938. Guiglia is retained because alternatives to monophyly of this genus are not well supported either. HeliorussusBenson, 1955, syn. nov. , is incorporated in Orussus Latreille, 1796; the species formerly included in Heliorussus, Orussus schoutedeni Guiglia, 1937, combination reestablished, O. scutator (Benson, 1955) comb. nov. and O. spinifer (Benson, 1955), comb. nov. are transferred to Orussus. Leptorussus kwazuluensis sp. nov. is described; Pseudoryssus emanuelis Guiglia, 1956 syn. nov. is considered a junior synonym of Pseudoryssus henschii (Mocsáry, 1910). An annotated key to the world species of Orussus is included as an appendix.