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

In this paper we diagnose the genus Sabroskya Schlinger, 1960 and describe Sabroskya schlingerisp. 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, 1987).

Acroceridae comprise approximately 520 species in 53 genera (Pape and Thompson 2011; Gillung and Winterton 2011) occupying most biogeographic regions. The family is presently classified in three extant subfamilies based on adult morphology and host specificity with Panopinae suggested as the most primitive and Acrocerinae the most derived, with Philopotinae supposedly occupying an intermediate position (Schlinger 1987; Schlinger 2009). Recent phylogenetic analyses using DNA sequence data suggest an opposite sequence of cladogenesis and that Acrocerinae are polyphyletic (Winterton et al. 2007).

Acrocerinae comprise 17 extant and 5 extinct described genera, found in all major biogeographical regions. The subfamily is distinguished from Philopotinae and Panopinae by the following characteristics: antennae styliform, postpronotal lobes widely separated, never medially contiguous, humeral crossvein rarely well developed, and tibial apical spines absent (rarely present) (Winterton in press). In phylogenetic analyses of DNA sequences for six sampled genera by Winterton et al. (2007), Meigen, 1803 and Philippi, 1865 were recovered as a sister clade to the rest of Acroceridae. The remaining acrocerine genera sampled (i.e. Gray 1832, Latreille, 1797, Schlinger, 1972, Gray, 1832, Philippi, 1865) were recovered in a monophyletic clade sister to Panopinae. displays very different adult and larval morphology from all other acrocerids, supporting this conclusion. Yet, the placement of as sister to is problematic as the adult morphology is more similar to Cole, 1966 than to and should be re-examined using both morphology and DNA sequence data.

Six genera of Acrocerinae are known from the Afrotropical Region, including the nearly cosmopolitan genera , and , as well as the endemic genera , Sabrosky, 1950 and Schlinger, 1960. includes two previously described species from South Africa ( Schlinger, 1960 and Barrclough, 1984) (Schlinger 1960a; Barraclough 1984) and can be readily identified from all other acrocerine genera by the presence of a cervical collar, antennae located adjacent to mouthparts, wing vein R4+5 straight, cell m3 absent and discal and basal r4+5 cells separate and closed. Herein we describe a new species of from Malawi and present a key to species. A key to living and fossil genera of Acrocerinae of the world is also presented.

Materials and methods

Terminology follows McAlpine (1981) and Schlinger (1981) as modified by Winterton (in press). The type specimen is deposited in the collection of the Tel Aviv University (TAU). Specimen images were taken at different focal points using a digital camera and subsequently combined into a serial montage image using Helicon Focus software. High-resolution digital images were deposited into Morphbank:: Biological Imaging with embedded URL links within the document between descriptions and MorpPageBreakhbank 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 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, Grimaldi & Hauser, 2011 and 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 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.

Acroceridae wings. Acrocerinae: A (Fabricius, 1794) B appendiculata Philippi, 1865. Scale line = 0.2 mm.

Schlinger

http://species-id.net/wiki/Sabroskya

Type species.

Schlinger 1960: 479 by original designation.

Diagnosis.

Body length: 6.0–7.0 mm. Body shape not arched. Head width slightly narrower than thorax; sub-spherical; postocular ridge and occiput rounded; three ocelli; posterior margin of eye rounded; eye pilose (dense); eyes contiguous above antennal base; antennae located adjacent to mouthparts; palpus present or absent; proboscis length less than head length, with sparse setal pile; flagellum stylate, apex with relatively large terminal seta; postpronotal lobes not enlarged or contiguous medially; antenotum expanded, collar-like behind head; subscutellum relatively enlarged; tibial spines absent; pulvilli present; wing hyaline or slightly smoky infuscate, markings absent; costa ending near wing apex; costal margin straight; humeral crossvein absent; R1 very slightly inflated at pterostigma; R2+3 present or absent; veins R4 and R5 present as single vein R4+5; radial veins straight, complete to wing margin; crossvein 2r-m present between M1 and R4+5, bisecting cell r4+5, cell formed by 2r-m narrow elongate; medial vein compliment: M1, M2 and M3 present (M3 fused with CuA1), medial veins may orPageBreak may not reach wing margin; discal cell closed completely; cell m3 absent; CuA2 fused to A1 before wing margin, petiolate; wing microtrichia absent; anal lobe well developed; alula well developed; abdominal tergites smooth, rounded; abdomen rounded, inflated, slightly wider than thorax.

Comments.

is a highly specialized Acrocerinae spider fly genus morphologically similar to , , and . 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 , , , and , all of which have a wing venation lacking cell m3. The Baltic amber genus is unique among this acrocerine clade as the wing retains remnants of cell m3, with spur veins present in cell d+m3 (Hennig 1968); similar remnants of m3 can also be found in more distantly related . 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 , and the costal margin has a membranous rim or flange between R1 and wing apex (Figs 2–3). This character still needs to be confirmed in , but appears to be likely a synapomorphy for the group. The putative sister genus to is , and both have similar wing venation comprising well defined and complete discal and basal r4+5 wing cells. These cells are absent in and are fused to form a single cell in . can be immediately identified from other acrocerine genera by the presence of a cervical collar, antennae located adjacent to mouthparts, R4+5 straight, cell m3 absent and discal and basal r4+5 cells separate and closed.

Figure 2.

Acroceridae wings. Acrocerinae: A Walker, 1852 B Paramonov, 1957 (female). Scale line = 0.2 mm.

Figure 3.

Acrocerinae: A, Schlinger, 1960a; B, sp. n.; C, sp. n., male head, lateral view. Scale line = 0.2 mm.

Schlinger (1960a) described the antennal flagellum of 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 (Schlinger 1960b) shows a similar condition as found in both sp. n. and , with the flagellum actually having large terminal setae present (Fig. 3C) (see also Grimaldi (1995: fig. 5)). Only in are palpi present while in and sp. n., the palpi are absent.

Included species.

Schlinger, 1960; Barraclough, 1984; sp. n.

Key to species of ..

(Females are unknown for and sp. n.)

sp. n.

urn:lsid:zoobank.org:act:1C52AA02-CD70-4B6E-B2E9-F236A6C1DEB4

http://species-id.net/wiki/Sabroskya_schlingeri

Figures 3B, 3C 4 -6

Figure 4.

sp. n., male, oblique view [Morphbank: 705550]. Body length = 5.0 mm.

Figure 5.

sp. n., male, lateral view [Morphbank: 705551]. Body length = 5.0 mm.

Figure 6.

sp. n., male, dorsal view [Morphbank: 705552]. Body length = 5.0 mm.

Type material.

Holotype male, MALAWI: Northern Province: North Viphya Mts, 1500 m, Rt. M1, 21–22.ix.1998, 10 km S Chikangawa [-11.929, 33.747], F. Kaplan, A. Freidberg (TAU).

Wing venation black; vein R2+3 absent; wing hyaline, smoky infuscate anteriorly; flagellum with subterminal seta present; lower calypter pile short, dark; PageBreakthoracic and abdominal pile black; palpi absent; hind coxae with setae on posterior surface; paler areas of abdominal tergites connected medially.

Description.

Body length 5.0 mm (male). Head. Eye brown, densely pilose with setae approximately length of tarsal claw; posterior margin of eye not emarginate; ocellar tubercle glossy black and raised around ocelli; occiput glossy black, coriacious, pile black; postocular ridge, gena to parafacial with narrow grey pubescent ridge; palpus absent; margin of oral cavity apilose; proboscis shorter than head length (Fig. 3C); antenna brown; flagellum apex with relatively elongate terminal seta, subterminal seta(e) present laterally. Thorax. Scutum glossy black with bronze suffusion anteriorly, postalar callus yellowish; vestiture as dense brown-black pile, paler on postalar callus; scutellum glossy black with dense black pile; pleuron glossy black with brown to yellowish pile; coxae black with yellow pile; femora dark yellow with black suffusion basally, pile yellow; tibiae yellow with short yellow pile; tarsi yellow; lower calypter hyaline with darkish margin; pile on membrane and along rim yellow to brown; wing hyaline, slightly smoky infuscate anteriorly, venation dark; vein R2+3 absent (Fig. 3B); M2 very short. Abdomen. Elongate globose, slightly wider than thorax, tergites dark brown anteriorly, yellow laterally and meeting posteromedially; covered with brown-black setae, erect and tufted medially on each tergite. Male genitalia: not dissected, externally similar to .

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 .

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 R2+3, dark vestiture and wing venation, and smoky infuscate wing readily differentiate this species from and

Schlinger, male, lateral view.

Schlinger, male, dorsal view.

Schlinger, female, lateral view.

Schlinger, female, dorsal view.

1	Cell m3 present and well formed (Fig. 1A)	2
–	Cell m3 clearly absent (Figs 1B, 2–3), or, fusion of m3 with discal cell indicated by presence of spur veins (rare)	10
2	Antennae not adjacent to the ocellar tubercle; located on middle of frons, separated from ocellar tubercle by distance much greater than length of ocellar tubercle (Figs 3C, 5)	3
–	Antennae adjacent to the ocellar tubercle	5
3	Wing vein R4+5 forking from R2+3 in distal half of cell r4+5; cells bm and br fused into a single cell; cell r4+5 relatively broad; eye emarginate (Burmese Amber)	Schlingeromyia Grimaldi & Hauser, 2012
–	Wing vein R4+5 forking from R2+3 before or at base of cell r4+5; cells bm and br separate; cell r4+5 relatively narrow along entire length; eye not emarginate	4
4	Eyes apilose; radial veins curved anteriorly, joining to anterior margin of wing (Southern Africa)	Psilodera Gray, 1832
–	Eyes pilose; radial veins relatively straight, joining wing apex (Chile)	Holops Philippi, 1865
5	Eyes very sparsely pilose, few microscopic setae present (India)	Subcyrtus Brunetti, 1926
–	Eyes densely pilose	6
6	Mouthparts longer than head; palpi present; proboscis not pilose	7
–	Mouthparts shorter than head; palpi apparently not present; proboscis pilose (Fig. 3C)	8
7	Antennae separated form ocellar tubercle by small depression (Europe) (Fig. 1A [wing])	Cyrtus Latreille, 1797
–	Antennae not separated from ocellar tubercle by depression (China)	Paracyrtus Schlinger, 1972
8	Mouthparts very short, barely protruding from oral cavity (Palaeartic)	Asopsebius Nartshuk, 1982
–	Mouthparts longer, protruding from oral cavity, but not longer than head	9
9	Labellum present; abdominal spiracles II - IV placed in intersegmental membranes (Taiwan)	Hadrogaster Schlinger, 1972
–	Labellum absent; abdominal spiracles II - IV placed in corresponding sternites (Taiwan and Japan)	Nipponcyrtus Schlinger, 1972
10	Antennae located on upper half of head, usually proximal to ocellar tubercle	11
–	Antennae located on lower half of head, adjacent to oral cavity	17
11	Vein R4+5 represented as a single unforked vein	12
–	Veins R4 and R5 forked and petiolate basally (R4 rarely incomplete basally)	14
12	Eyes minutely pilose, setae barely evident; petiolate to wing margin; flagellum with minute terminal seta; male genitalic capsule enlarged and bulbous (Chile) (Fig. 1B)	Sphaerops Philippi, 1865
–	Eyes clearly pilose; flagellum with relatively large terminal seta; male genitalic capsule not enlarged or bulbous	13
13	Microtrichia on the wing membrane absent; A1 joined to wing margin separate from CuA2 (Baltic Amber)	Villalites Hennig, 1966
–	Microtrichia on the wing membrane present; A1 and CuA2 approximated distally but incomplete, not joined to wing margin (Chile)	Villalus Cole, 1918
14	Wing with single medial vein (M3?); cell bm only well defined, other cells reduced or merged to form single cell open basally; alula well developed (most biogeographic regions)	Acrocera Meigen, 1803
–	Wing with three medial veins originating from discal cell; wing with three or four wing cells well defined; alula present or absent	15
15	Mediolobus absent; crossvein 2r-m absent so that only three closed wing cells present; antennal style longer than rest of flagellum (Burmese Amber)	Burmacyrtus Grimaldi & Hauser, 2011
–	Mediolobus present and similar shaped to pulvilli; crossvein 2r-m present so that four closed wing cells are present; antennal style shorter than rest of flagellum	16
16	Anterior ocellus reduced but present; costa circumambient; male wing with anterior costal process (Nearctic)	Turbopsebius Schlinger, 1972
–	Anterior ocellus absent; costa ending in radial field near wing apex; male wing without anterior process (Palaearctic)	Opsebius Costa, 1855
17	Wing with remnants of cell m3 indicated by presence of spur veins in cell d+m3 (Hennig 1968: figs 5, 8) (Baltic Amber)	Glaesoncodes Hennig, 1968
–	Wing cell m3 not indicated by spur veins	18
18	Wing cells d and basal r4+5 separate; antepronotum produced anteriorly as collar-like process behind head (Schlinger 1960a: fig. 13)	19
–	Wing cells d and basal r4+5 (and m3) fused to form large single cell (Fig. 2B), or cells absent (Fig. 2A); antepronotum not forming collar-like process behind head	20
19	Thorax greatly enlarged dorsally; wing veins R2+3 and R4+5 curved anteriorly then reflexed towards wing apex; vein M2 reaching wing margin; alula absent  (Kenya) (Sabrosky 1950: fig. 2a)	Meruia Sabrosky, 1950
–	Thorax rounded but not greatly enlarged; radial veins straight; vein M2 not reaching wing margin; alula present (southern Africa) (Figs 3–10)	Sabroskya Schlinger, 1960
20	Tibial spines present apically; mouthparts present (Cosmopolitan) (Fig. 2B)	Pterodontia Gray, 1832
–	Tibial spines absent; mouthparts absent, oral cavity closed (Cosmopolitan) (Fig. 2A)	Ogcodes Latreille, 1797

1	Flagellum with subterminal setae absent; palpi present; posterior surface of hind coxae apilose; paler areas of male abdominal tergites not connected medially (South Africa)	Sabroskya palpalis Barraclough, 1984
–	Flagellum with subterminal setae present (Fig. 3C); palpi absent; posterior surface of hind coxae pilose; paler areas of male abdominal tergites connected medially	2
2	Male wing venation brown; vein R2+3 absent (Fig. 3B); wing smoky infuscate anteriorly; thoracic, abdominal and lower calypter pile dark (Malawi) (Figs 3–6)	Sabroskya schlingeri sp. n.
–	Male wing venation white, brown in female; vein R2+3 present (Fig. 3A); wing hyaline; thoracic, abdominal and lower calypter pile white (South Africa) (Figs 7–10)	Sabroskya ogcodoides Schlinger, 1960