A new species of spider fly in the genus Sabroskya Schlinger from Malawi, with a key to Acrocerinae world genera (Diptera, Acroceridae)

Abstract In this paper we diagnose the genus Sabroskya Schlinger, 1960 and describe Sabroskya schlingeri sp. n. from Malawi. We also provide dichotomous keys to species of Sabroskya and to world genera of the subfamily Acrocerinae, both extant and extinct.


Introduction
Spider flies (Diptera: Acroceridae) are a geographically cosmopolitan group although most species are relatively rarely collected. Adults have a distinctive morphology and a wide diversity of form, but typically with a small head, greatly enlarged lower calypter and swollen abdomen. Larvae are parasitoids of spiders, with a hypermetamorphic life cycle consisting of four instars (Schlinger 1981(Schlinger , 1987. bank images. All new nomenclatural acts and literature are registered in Zoobank (Pyle and Michel 2008).
taxonomy Key to Acrocerinae genera of the World: The extinct genus Juracyrtus Nartshuk, 1996 is not included as it is represented by a compression fossil and lacks sufficient detail to be thoroughly differentiated from other genera. Two recently described genera, Schlingeromyia Grimaldi &Hauser, 2011 andBurmacyrtus Grimaldi &Hauser, 2011, from Cretaceous aged amber (Grimaldi et al. 2011) are included here in Acrocerinae based on the presence of stylate antennae, non-arched body shape and widely separated postpronotal lobes. The placement of Burmacyrtus in Acroceridae is problematic and should be reassessed as this genus lacks characters typical of acrocerids, including a mediolobus and wing crossvein 2r-m, and has a relatively small calypter. Based on these characters, placement in Heterodactyla should be considered rather than in Acroceridae, although a stem-group position for the genus as suggested by Grimaldi et al. (2011) may also be reasonable.
Comments. Sabroskya is a highly specialized Acrocerinae spider fly genus morphologically similar to Meruia, Ogcodes, Glaesoncodes and Pterodontia. These five genera all have stylate antennae located on the lower side of the head adjacent to the often reduced or absent mouthparts. Other acrocerine genera related to this clade include Turbopsebius, Opsebius, Villalus, Acrocera and Sphaerops, all of which have a wing venation lacking cell m 3 . The Baltic amber genus Glaesoncodes is unique among this acrocerine clade as the wing retains remnants of cell m 3 , with spur veins present in cell d+m 3 (Hennig 1968); similar remnants of m 3 can also be found in more distantly related Turbopsebius. This provides important insights into the evolution of acrocerid wing venation, suggesting rampant reduction in number of cells and veins through loss or fusion, and can be found in derived clades in all three extant subfamilies (Winterton et al. 2007;Gillung and Winterton 2011).
In Pterodontia, Sabroskya and Ogcodes the costal margin has a membranous rim or flange between R 1 and wing apex (Figs 2-3). This character still needs to be confirmed in Meruia, but appears to be likely a synapomorphy for the group. The putative sister genus to Sabroskya is Meruia, and both have similar wing venation comprising well defined and complete discal and basal r 4+5 wing cells. These cells are absent in Ogcodes and are fused to form a single cell in Pterodontia. Sabroskya can be immediately identified from other acrocerine genera by the presence of a cervical collar, antennae located adjacent to mouthparts, R 4+5 straight, cell m 3 absent and discal and basal r 4+5 cells separate and closed. Schlinger (1960a) described the antennal flagellum of Sabroskya as stylate without a terminal seta, and with a large subterminal seta on the lateral surface of the flagellum. Detailed examination of the topotype series of S. ogcodoides (Schlinger 1960b) shows a similar condition as found in both S. schlingeri sp. n. and S. palpalis, with the flagellum actually having large terminal setae present (Fig. 3C) (see also Grimaldi (1995: fig. 5)). Only in S. palpalis are palpi present while in S. ogcodoides and S. schlingeri sp. n., the palpi are absent.
Etymology. The specific epithet is named in honor of Evert I. Schlinger, a foremost expert on world Acroceridae taxonomy and patron of dipterology. Evert Schlinger had previously identified that this specimen represented a new species of Sabroskya.
Comments. Sabroskya schlingeri sp. n. is known only from a single male specimen from Malawi. A label on the pin of the holotype indicates that E. I. Schlinger had recognized that this species was a new taxon separate from the two previously described species. This is the most northern record for the genus, with both previously described species recorded from Eastern Cape and KwaZulu-Natal Provinces of South Africa. The lack of vein R 2+3 , dark vestiture and wing venation, and smoky infuscate wing readily differentiate this species from S. palpalis and S. ogcodoides.