The first Mesozoic stephanid wasp (Hymenoptera: Stephanidae)

Abstract

The stephanid wasps are of great phylogenetic and biological significance among parasitic Hymenoptera, itself one of the major radiations of insects and of critical ecological and agricultural importance. The family, the only one of its superfamily (e.g., Gauld and Bolton, 1988; Goulet and Huber, 1993: although Rasnitsyn, 1988, 2000 includes the traditional Trigonalyoidea, Megalyroidea, Ceraphronoidea, and some extinct lineages in the Stephanoidea), is hypothesized by some authors to be basal within the diverse parasitoid lineage Apocrita (Rasnitsyn, 1975, 2000; Königsmann, 1978; Rohdendorf and Rasnitsyn, 1980; Whitfield, 1992, 1998; Vilhelmsen, 1996, 2001). Such a phylogenetic placement makes the stephanids an interesting link between the principally xylophagous wood wasps (i.e., the paraphyletic suborder Symphyta), the sole parasitic symphytan family Orussidae, and the remainder of the Apocrita (Orussidae + Apocrita = Euhymenoptera). Thus, stephanids may represent one of the earliest families of parasitoid wasps exhibiting the characteristic “wasp waist,” allowing for more control and flexibility during oviposition. Tantalizingly, the stephanids are morphologically similar to orussids in that both exhibit a characteristic series of tubercles on the head (presumably an adaptation for allowing them to move through burrows in wood after eclosion). These similarities, however, may be convergent adaptations of parasitizing wood-boring insects (a plesiomorphic biological trait across the Apocrita) and stephanids may belong to a clade of evaniomorphous wasps, albeit still relatively basal within that lineage (e.g., Rasnitsyn, 1988; Ronquist et al., 1999). In either case, Stephanidae figure prominently in cladistic studies of the Hymenoptera and are of presumably ancient origin based on their phylogenetic position (e.g., Rasnitsyn, 2000). Fossils of the family, however, are rare and until now have been restricted to Tertiary deposits.