Stackelberginia cerberus, Mcknight & Cannings, 2017

Mcknight, Tristan A. & Cannings, Robert A., 2017, Description and phylogenetic classification of Stackelberginia cerberus sp. nov. (Diptera: Asilidae), comprising the first record of this genus from the Nearctic, Zootaxa 4306 (4), pp. 567-579 : 571-574

Stackelberginia cerberus sp. nov. McKnight

Diagnosis. A small grey species similar to Lasiopogon but with facial swelling mostly flattened; mystax confined to lower facial swelling; bristles of ocellar triangle, thorax, and legs extremely long and strong; occipital setae strong and straight; tarsal claws unusually large; metacoxa with anterior peg blunt; cuticle dark brown or black except for ferruginous tibiae and tarsi, mostly covered in grey tomentum; genitalia ferruginous, hypopygium rotated 120° and epandrium completely divided medially, narrow ( Figs 1 , 2 ).

Description. Body length ♂ 8.5–10 mm; ♀ 8.5–11.5 mm.

Head. Cuticle black; tomentum of face silver, vertex and occiput grey. Facial swelling greatly reduced, leaving only a slightly swollen angle above oral margin but otherwise not extending beyond eyes in lateral view. All setae on head white except ocellar and orbital bristles, which are typically chestnut brown. Mystax setae long, loosely clumped over oral margin with a small gap dorsomedially; frons with a clump of short, thick setae midway between antennae and ocellar triangle; one long, strong orbital seta anteriorly inclined, occasionally with another short fine seta; ocellar triangle with two long, strong setae and several short fine hairs anteriorly inclined along posterior edge, longest bristle to 0.7mm; occipital bristles erect, relatively short and straight, in lateral view extending ventrally to midpoint of eye. Palps with fine white hairs along length; robust setae on postgena.

HW ♂ 1.48–1.88mm; ♀ 1.64–1.88mm. FW ♂ 0.28–0.34mm; ♀ 0.32–0.35mm. VW ♂ 0.66–0.73mm; ♀ 0.67– 0.77mm. GL ♂ 0.25–0.28mm; ♀ 0.25–0.33mm. VW/HW = ♂ 0.39–0.45; ♀ 0.41. FW/VW = ♂ 0.42–0.46; ♀ 0.46– 0.48. VD/VW = ♂ 0.10–0.14; ♀ 0.12–0.13. GH/GL = ♂ 0.43–0.52 ♀ 0.42–0.48.

Antennae. Dark brown, base of pedicel pale brown. Robust white setae on scape and pedicel. Postpedicel rectangular with a slight bulge at midlength; stylus long, with pronounced apical spine. WPP/LPP = ♂ 0.22; ♀ 0.20–0.21. LAS/LPP = ♂ 0.50; ♀ 0.67–0.70.

Thorax. Thoracic cuticle dark brown, covered in thick grey tomentum. Prothorax with hairs white; postpronotal lobes chestnut brown with lateral angle reddish, hairs white; postalar lobes reddish. Scutum tomentum grey, without stripes or spots; short hairs sparse, white around perimeter and brown/black over dorsum. Dorsocentral bristles brown, prominent (longest to 0.85mm), 1 anterior and 2 posterior to transverse suture. Lateral bristles of the scutum brown, very long (longest to 1.3 mm): one postalar, one supra-alar, and two notopleural (one each of the presutural and posthumeral subgroups of Cannings 2002). Scutellum covered in grey tomentum, without impressed rim, bare on disc, 5-6 long white bristles apically with a few short fine hairs just inside.

Pleural tomentum grey, all hairs and bristles white. Katatergal setae 6–7 with a few finer hairs mixed dorsally; katepisternal setae fine, short; anepisternum with 2 long, prominent setae (longest 1.2mm) at posterior edge and a patch of fine hairs along dorsal margin; anepimeron without setae. Antepronotum with 8–12 fine setae; proepisternum with 4–6 strong long setae and 0–2 fine hairs.

Legs. Cuticle black except reddish tibia, trochanters, extreme medial and apical tips of femorae, and tarsal bases; tomentum grey, very thin below femora. Anterior face of metacoxa bear pronounced peg with apex rounded, not tapered; 2 fine setae projecting ventrally at base of peg. All hairs and bristles of legs white except on tarsi, where mostly brown. Coxae with dense, long, strong bristles facing anteriorly (on procoxa) or laterally (on meso- and metacoxa); 40+ on procoxa, 3–12 on mesocoxa, 4 on metacoxa. Femora with fine, short procumbent hairs and strong erect bristles; 5–6 ventral bristles longer than adjacent hairs on pro- and mesofemur, metafemur with only fine hairs just longer than surrounding setae. Apical and dorsolateral bristles strong, numerous: profemur with 3–5, mesofemur with 2–4, metafemur with 5–7. Bristles on tibiae and tarsi strong, long; protibia with longest bristle 3.5x longer than tibial width. Tarsal claws large, with reddish base and black apices.

Wings. Veins yellow to dark brown, darker apically; membrane hyaline, slightly brown in oblique view. DCI = 0.52–0.58; cell m3 broadly open; cell cu p (sensu McAlpine 1981; cu a sensu Wootton & Ennos 1989) just closed at wing margin, varying from slightly stalked to slightly open in different individuals. Halter cream to light brown; knob without dark spot.

Abdomen. Tergite base color dark brown, light brown apically; covered in pale grey tomentum without other patterning. Tergite 1 with 6–8 strong bristles basolaterally, other tergites with strong short lateral setae, longest apically. Lateral setae white, dorsal setulae white laterally, black near midline. Sternite tomentum grey; setae white; sternite 1 with clump of 5–8 prominent erect setae. Tergite 8 red, visible between tergite 7 and terminalia. Terminalia red, with long hairs (white in male, black in female), in male rotated ~120° to one side.

Male genitalia. Epandrium and gonocoxite-hypandrial complex reddish-orange with darker apices, without tomentum, clothed in long white setae. Epandrium completely divided medially, in lateral view each half with width about 48% the length, widest at apex, ventral and dorsal margins mostly parallel, slumping ventrally, apex truncate with rounded corners. In dorsal view, medial margins of epandrial halves very shallowly concave, almost straight. Epandrial apodeme shallow; basal sclerite absent ( Cannings 2002).

Gonostylus elongate, slender, curved dorsally like a hooked finger, with another point dorsolaterally at the base. Long hairs over basal part of gonostylus. Gonocoxite-hypandrial complex in ventral view with width about 86% the length, partially fused laterally, medial transverse slit semicircular with distally pointed apex. Medial setal brush on gonocoxite-hypandrial complex white, setae long but relatively sparse compared to Lasiopogon . Gonocoxal apodemes long, in lateral view exposed length about 70% the basal width of the hypandrium; apodeme with sclerotized web ventrally.

Phallus paramere sheath long and slender, curved ventrally like a goose neck. Dorsal carina a low ridge no wider than the paramere sheath itself that follows the curvature of the paramere sheath and terminates before the apex without a notch. Subepandrial sclerite V-shaped; triangular medial unsclerotized portion in basal 65%; spines slender, attenuate, sparsely scattered over surface.

Female genitalia. (Undissected) Hairs on segment 8 dark brown/black, erect, abundant. Tergite 8 black, sternite 8 red/yellow, hypogynial valves dark brown, with many dark hairs; lateral lobe with dark setae; acanthophorite spines black, 3 on each half.

Type Material. HOLOTYPE. ♂ labelled: "[rectangular white label] NEV: Nye Co: NTS [Nuclear Test Site]/ Rock Valley/ IX-12-76, can tr./E.L. Sleeper et al."; “[rectangular white label]?/ det. EMFisher”; “[rectangular white label] FISH”; “[rectangular white label] mirus”. A holotype label "HOLOTYPE/ Stackelberginia / cerberus / des. T.A. McKnight 2017 [red, black-bordered label]" has been attached to this specimen. USNM type #USNMENT01295437. Both antennae are missing the postpedicel.

PARATYPES (8 designated, including 3 with genomic DNA extracts). U.S.A.: Nevada, Clark Co: Wheeler wash 6 mi NE of Pahrump, N 36.24678° W 115.89428°, elev: 1251 m, 5.x.2013, T.A. McKnight (1♀ [ DNA voucher] UMMZ-TAM-509-1, 1♀ [ DNA voucher] UMMZ-TAM-509-2; 1♀ [EtOH] UMMZ-TAM-509-3; 1? [damaged by dermestids] UMMZ-TAM-509-4); Nye Co : NTS [ Nuclear Test Site ] Rock Valley can tr., 3.x.1975, E.L. Sleeper (1♀ [dissected] RBCM ENT017-001946 ), 12.ix.1976, E.L. Sleeper (1♂ [dissected] RBCM ENT017- 001945 ); Rock Valley wash jct Hwy 95, 5 mi E of Amargosa Valley city, N of hwy, N 36.63359° W 116.31018° elev: 878 m, 6.x.2013, T.A. McKnight (1♀ [ DNA voucher] UMMZ-TAM-512-1; 1♀ FISH).

Type Locality. U.S.A.; Nevada, Nye Co., Nuclear Test Site, Rock Valley [N 36.694° W 116.179°].

Taxonomic Notes. This species was included in Cannings (2002) as “L. unc- 7 sp. nov.” and had been assigned a manuscript name of “mirus” because it was thought to be a miraculously unusual Lasiopogon . This epithet was changed after reclassification outside Lasiopogon .

Etymology. Latin Cerberus from the Greek Κέρβερος, used as a noun in apposition, named in similarity to the hound guarding the gates of the underworld in Greek mythology. The type locality for this predator is just outside the boundaries of both Death Valley National Park (the lowest elevation in North America) and the Yucca Mountain nuclear waste facility—sites with a suitably Hadean flair.

Distribution. Nearctic: USA; known only from two sites in the Amargosa desert of southwestern Nevada. Previously described species of Stackelberginia are known from deserts in Kazakhstan and Turkmenistan ( Fig. 3); we have summarized localities from the literature ( Lehr 1964, 1980) below with estimated georeferenced coordinates:

S. gracilis : Kazakhstan: Almaty Oblast: River Ila at Ayakkalkan resort, sandy crest among gravel, claypan, and marshy hollows on left bank [N 43.861° E 78.424°], 7.ix-9.x.1952 (number of specimens not noted); Mangishlyak Peninsula: Baskuduk district , salt flats and claypan amidst marshy hollows and dune chains [N 43.696° E 51.227°], 7.ix.1960, col. P.A. Lehr (1♂).

S. tsharykulievi : Turkmenistan: Mary: Leskhoz , desert region, on sand [N 37.291° E 62.351°], 9.x.1959, col. D.M. Charykulievi (1♂ 2♀).

Natural History. Habitat: sandy dry desert washes, usually found perching on fist-sized rocks in sandy areas near clumps of vegetation ( Fig. 4 ). One female was observed preying on a slightly-smaller fly (not collected). The fall flight period (12 September–6 October) is distinctive within the subfamily.

Other assassin flies were also active at the Stackelberginia sites at the same time. These were identified using keys in Wood (1981) and Wilcox (1961, 1965, 1966) and voucher specimens have been deposited at the RBCM and UMMZ: Hodophylax basingeri Pritchard , Cophura fisheri Wilcox , Efferia (Aridefferia) basingeri Wilcox.

Phylogeny. The species tree supports Stackelberginia as sister to Lasiopogon , and this clade as sister to the rest of the subfamily ( Fig. 5 ); these relationships were also recovered in each of the four individual gene trees (not shown). Node posterior probabilities are reasonably high (± 0.92) throughout the tree, except for some uncertainty for phylogenetic relationships within Lasiopogon and at the Stichopogoninae root. Lower support values for the subfamily root appear to stem from a basal polytomy in COI; this locus is known to have trouble resolving deeper level phylogenetic relationships ( Matsuda et al. 2014). Intrageneric relationships within Lasiopogon and Stichopogon will be covered in future publications with more comprehensive taxon sampling, but the overall genus-level topology matches our prior expectations from morphology—e.g., Townsendia grouping with Stichopogon , and the Asilinae ( Proctacanthus Macquart ) and Ommatiinae ( Ommatius Wiedemann ) clustering together in the outgroup.

Figures

FIGURE 1. Stackelberginia cerberus sp. nov. female habitus and head detail. The male differs only in the terminalia, which are presented in Fig 2.

FIGURE 2. Stackelberginia cerberus sp. nov. genitalia detail: A) epandrium, dorsal; B) epandrium lateral; C) gonostylus, apical; D) subepandrial sclerite, ventral; E) gonocoxite + hypandrium complex, ventral; F) gonocoxite + hypandrium complex, lateral; G) female ovipositor, lateral; H) phallus, lateral. Scale bars are 0.2 mm.

FIGURE 4. Habitats where Stackelberginia cerberus sp. nov. were collected in Nevada (see specimen list for more precise locality data): A) Clark Co.: Wheeler wash; B) Nye Co.: Rock Valley wash. Individuals were caught perching on small stones and sand along the washes.

FIGURE 5. Species tree for representatives of Stackelberginia, Lasiopogon, Stichopogon, Townsendia, and Asilidae and Mydidae outgroups, estimated via Bayesian inference in STARBEAST 2 from one mitochondrial locus (COI) and three nuclear protein coding loci (wingless, PEPCK, AATS). Branch labels show support for nodes when posterior probability <1.