The small wasp family Rhopalosomatidae consists of four extant genera: Rhopalosoma Cresson, Liosphex Townes, Paniscomima Enderlein, and Olixon Cameron (Townes, 1977; Guidotti, 2007). Species of Olixon are remarkable in being brachypterous while the other genera are fully winged. Eleven species of Olixon have been described from the following regions: the New World (three species), Africa (four species), Madagascar (two species) and Australia (two species) (Townes, 1977; Fernandez & Sarmiento-M, 2002; Lohrmann & Ohl, 2007) (see Fig. 1). Olixon is the only rhopalosomatid genus recorded from Australia. Members of this genus are 2.5–10 mm in length and are ant-like in appearance (Fig. 2). Their biology is poorly known, and the only confirmed host record is for the Australian species O. australiae, a parasitoid of trigonidiine crickets (Orthoptera: Gryllidae) (Perkins, 1908). Townes (1977) mentions ‘circumstantial evidence’ for wood crickets (Nemobius spp.) as hosts of O. banksii (Brues) in the Nearctic, and scaly crickets (Cycloptilum spp.) as hosts of O. testaceum Cameron in the Neotropics.
Specimens of Olixon were considered until recently to be extremely rare, as indicated by Townes (1977), who located fewer than 40 specimens in the world’s collections. Some of these specimens had been seen running singly over the ground and were collected by hand. Recently, flight intercept traps (Upton, 1991) and especially pitfall traps have been used more frequently in biological surveys and these have proved to be very effective in collecting Olixon. Over the past 15 years these traps have collected hundreds of specimens from various localities in Australia. A close examination of this material has revealed a surprisingly high species diversity. In this study, we record 17 species from Australia, of which 15 are new, thus more than doubling the number of species known world-wide.
We present the results of a cladistic analysis including nearly all (24 of 26) of the known world species of Olixon based on morphological characters. This analysis focuses on the relationships among the Australian Olixon, and the geographically isolated species from Madagascar, Africa and the New World, to examine the phylogenetic affinities and origins of the Australian fauna. In addition, we discuss the distribution and possible habitat preferences for the Australian species, describe all new taxa, and present a key for their identification.