Psilidae Macquart 1835

Psilidae Macquart, 1835

(Figs 1–48, 395–398)

Type genus: Psila Meigen 1803: 278, by Macquart (1835: 416) [as Psilomydae after unjustifiable name change of Psila to Psilomyia by Latreille (1929); Loxoceridae proposed in same paper (p. 372)]. Type species of genus: Musca fimetaria Linnaeus 1761: 458, by subsequent designation [Westwood 1840: 146].

The Psilidae are a group of mostly north temperate flies with 335 described species in three subfamilies globally (Shatalkin & Merz, 2010). One common name applied to the family is “rust fly”, because the larva of Psila hennigi (known until recently as Psila rosae (Fabricius)) produced rust-like traces and decay in the root of its hosts, including carrot, parsnip and turnip. Adult Psilidae have a thick coat of long, dense setulae that emerge from pits, and the shape of the face (Figs 3, 18) and the absence of the precoxal bridge are also quite characteristic, as is the shape of the wing and its venation, including the peculiar curvature of vein R 1 past the subcostal break (Figs 395–398), the latter of which is quite evident in the fossil Electrochyliza. Early family and genus-level treatments of this species-rich group include Capelle (1953), Frey (1925a, 1955), Hennig (1941b), Johnson (1920) and Melander (1920). More recently, the Old World fauna has been revised by Iwasa (1989, 1991, 1994), Shatalkin (1983, 1986, 1989, 1998 a, 1998b) and Wang & Yang (1996); the New World fauna was treated by Buck & Marshall (2006a, 2006b). Regional catalogues are provided in Shewell (1965) [Nearctic], Soós (1984d) [Palaearctic], Cogan (1977, 1980b) [Oriental, Afrotropical], Evenhuis (1989d) [Australian] and Prado (1975) [Neotropical]. The fauna of all Regions requires revision.

The subfamily Psilinae (Figs 6–9, 17–18) is mostly north temperate in distribution, and includes 216 species (Shatalkin & Merz, 2010). While it occurs in all biogeographic regions, the few known Neotropical species are restricted to Central America from Mexico to Costa Rica (Buck, 2010). The subfamily is split between Psila and Loxocera, which were redefined by Buck & Marshall (2006a, 2006b) using adult external, adult genitalic and egg morphological characters. Buck (2010) mentions that six subgenera are recognized in Psila s.l., with the monophyly of some of these subordinate taxa still to be properly established— Psila Meigen s.s., Asiopsila Shatalkin, Psilosoma Zetterstedt, Freyopsila Shatalkin, Synaphopsila Hendel and Xenopsila Buck. Afropsila Shatalkin, Chamaepsila Hendel, Oxypsila Frey and Tetrapsila Frey should also be included among these. Three subgenera were included in Loxocera s.l. — Loxocera Meigen s.s., Tropeopsila Shatalkin and Imantimyia Frey. Groups requiring special consideration include the Afrotropical Loxocerosoma Verbeke with three species, likely considered to be synonymous with Loxocera (Buck & Marshall, 2006b), and the monotypic Loxochyliza Verbeke from Nepal, which is presently unplaced (see Shatalkin (1998)). The east Palaearctic Tropeopsila Shatalkin (two species) is presently treated as a subgenus of Loxocera, but Buck & Marshall (2006b) consider its position in need of verification.

Chylizinae (Figs 1–5) includes the single genus Chyliza, with 118 described species (Shatalkin, 2014). The genus is global in distribution, and the only psilid known from South America (Buck, 2010), but it is best represented in the Australian and Afrotropical Regions (Shatalkin, 1998a). Subgenera have been proposed for the genus, but Shatalkin (1998) is followed here in considering these as likely synonyms because they are based on few and likely homoplastic characters that likely do not reflect natural groupings. As an alternative to the existing subgenus system, Shatalkin (1998) provided a preliminary three-group subdivision of the genus based on colour. Future considerations of genus subdivision should be based on the results of a more thorough phylogenetic analysis.

Belobackenbardiinae (Figs 10–18) contains three species in the South African genus Belobackenbardia Shatalkin. Shatalkin (2002) considered the most ancestral lineage of Psilidae, and defined it in part by a brush of short white hair on the postgena (not close to eye margin as similar hairs in Chyliza; also found in some Loxocera), a basally bushier arista, and a relatively large epandrium fused to large, apically bilobed surstyli; one pair of large dorsal epandrial processes occur in most species. An additional synapomorphy proposed by Shatalkin (2002) is a long, curved phallus, but this is here interpreted as the pregonite, with the actual phallus ventromedial to these structures, being small and mostly membranous. There are likely additional synapomorphies of the male genitalia, but only a single species was examined for this study and the genitalia of the other species are not figured in the literature.

The only accepted fossil Psilidae is Electrochyliza Hennig, which contains the single species E. succini Hennig (Eocene/Oligocene Baltic amber), although at least one other species of Electrochyliza is present in the Hoffeins collection. The visible external male genitalia bear a resemblance to those of Psilinae, but not much more can be inferred at present. The monotypic Psilites Heer (Miocene compression fossil, Croatia) [not examined] was excluded from the family by Gentilini et al. (2006), who suggested that it might actually be a tephritoid. An unidentified Psila species was mentioned by Schöberlin (1888) (Miocene compression fossil, Switzerland), and unidentified Psilidae in amber are mentioned in Tschirnhaus & Hoffeins (2009).

Biology. Adults of Nearctic Psilidae are often found on foliage and sometimes fallen wood in closed woods, and Old World species are found in dense vegetation in regions that experience high rainfall, including areas of high elevation (Cogan, 1977). An unidentified Loxocera has been observed feeding on insects, likely scavenging (S.A. Marshall, pers. comm.).

Larvae are known to be primary feeders on living plants in stems, roots, bulbs and under the bark of thin twigs on trees (Shatalkin & Merz, 2010). Psila s.l. species develop in the stems and roots of a variety of grasses and other herbaceous plants, including the carrot rust fly (Psila hennigi (Thompson & Pont); Figs 17–18, 47), which can be a significant pest of umbelliferous crops such as carrot and celery (Degen et al., 1999; John et al. 2001; Collier & Finch, 2009). Originally Palaearctic in distribution, the carrot rust fly is now known in Canada, the United States, Cuba, South Africa and New Zealand (CABI, 1992; Botha et al., 2001). Psila fimentaria (L.) is known from Carex. Monocots serve as hosts for the larvae of the less commonly encountered Loxocera, including Carex (Valley et al., 1969), Juncus (Chandler, 1975b; Ferrar, 1987), Digitaria (Capelle, 1953) and possibly Luzula (Chandler, 1975b), which may have driven the development of the laterally compressed ovipositor characteristic of that genus (Buck, 2010).

Larvae of north temperate Chyliza are known to feed on living trees and herbs (Chandler, 1975b; Ferrar, 1987) in at least 10 plant families (Sueyoshi, 2013), and Capelle (1953) found larvae in rotting wood. Chyliza notata has been observed ovipositing on fresh tree wounds where the larvae tunnel into the living tissue; pupation occurs just under the bark (Ferrar, 1987). Chyliza leptogaster (Panzer) has been recovered from deciduous trees and is known to cause phloem necroses; C. annulipes Macquart is found in conifers and are associated with wounds. Chyliza have also been found under the bark of trees housing buprestids (Gates et al., 2006), with initial introduction in trees apparently occurring through existing wounds in the plant (Lyneborg, 1987). Sugiura & Yamazaki (2006) found larvae of Chyliza in galls induced by Cecidomyiidae species, Yamazaki & Sugiura (2008) found C. splendida in Wisteria galls induced by bacteria, and in some cases the psilid larvae appear to have induced the gall itself (Chandler, 1975b; Ferrar, 1987). Precopulatory, copulatory and oviposition behaviour of Chyliza vittata on a leafless orchid (Gastroda elata) was described by Sugiura (2016), but other orchids are also known to serve as hosts where the larva feeds internally on leaves, stems and underground tissue (Suetsugu, 2016).

Immature stages. Psiline larval morphology was described for two Loxocera in Meijere (1941, 1945), and the eggs of Loxocera and Psila species were thoroughly described in Buck & Marshall (2006a, 2006b). Illustrations and descriptions of immature stages of Chylizinae and Psilinae are also available in Ferrar (1987), who provides references to original sources in the literature.

Adult Diagnosis. Medium-sized, often narrow-bodied; dorsum with shallow to deep pits at base of setae and setulae, at least on notum. Orange to yellow with brown to black pattern, or predominantly dark. Antenna elbowed; pedicel with dorsal seam; first flagellomere slightly to very elongate. Face usually with angled ventromedial plate with transverse striations; sometimes strongly receding ventrally (very broadly so in some Psilinae); ocelli slightly shifted anteriorly, distant from postocellar; ocellar tubercle and space anterior to postocellars with patch of setulae. Vibrissa absent; ocellar seta usually very long when present. Anterior spiracle in ovate depression with grooves sometimes forming a pit (Fig. 17); thorax covered with long, dense setulae (also Somatia, Megamerinidae), at least dorsally but sometimes also laterally and ventrally. Cell br narrowed on distal section (Figs 395–398); costa with subcostal break; subcosta continuing to costa at near right angle as hyaline weakening in membrane; similar to Opomyzidae, vein R 1 distal to subcostal insertion usually long and slightly to more broadly arched (exaggerated in Chylzinae (Fig. 396), narrow and straight in Belobackenbardiinae).

Adult Definition. Medium-sized, often narrow-bodied flies (Figs 1–18, 47–48); body length 3.0–12.0mm. Surface well-sclerotized with shallow to deep pits (sometimes forming transverse striations) dorsally at base of setae and setulae, at least on notum. Orange to yellow with brown to black pattern, or predominantly dark with halter often pale (knob rarely dark); arista black to white.

Chaetotaxy: 1 inner vertical; 1–2 outer verticals; 0–2 fronto-orbitals; 0–1 ocellar (often very long when present, potentially extending to eye margin); 0–1 postocellar (divergent); vibrissa absent. Pedicel often densely setulose, sometimes with longer marginal seta(e) dorsally and ventrally. Frontal vitta with numerous scattered rows of setulae, often inclinate and/or proclinate medially and anteriorly, continuing posteriorly onto occiput and postgena, dense in Chylizinae (Fig. 4); vitta sometimes velvety; ocellar tubercle setulose, separated from postovertical by similarly setulose patch; parafacial and/or sides of face microtomentose; venter of gena and parafacial with row of setulae. 0 presutural intra-alar; 0–1 postpronotal; 0 anterior notopleural; 0–1 posterior notopleural; 2 posterior supra-alar; 0 posterior intra-alar; 1–4 dorsocentrals; 0–1 acrostichals; 2–3 scutellars (uncommonly 1 or 4); 0 proepisternal; 0 anepisternal; 0 katepisternal. Body largely covered with dense, short setulae; proepisternum with patch of white microtrichia (restricted to ventral margin or extending to encompass ventral half of sclerite, and sometimes extending to spiracle; absent in Belobackenbardiinae); setulae on scutum with partings and crowns that are distinct as in Megamerinidae (Chylizinae (Fig. 1)) or inconspicuous to absent; pleuron sparsely setulose posterior to wing base, mostly densely setulose anterior to wing base with bare patches, sometimes with conspicuously downturned patch of setulae along venter of anepisternum. Scutellum bare to sparsely setulose or microtomentose; remainder of metanotum microtomentose to setulose, with katatergite most conspicuously and densely haired and mediotergite sometimes bare. Mid tibia with one distinct ventroapical seta, sometimes accompanied by additional smaller seta; hind tibia sometimes with ventroapical seta.

Head. Antenna elbowed (Fig. 5); pedicel with dorsal seam; arista pubescent to short plumose, rarely flattened, inserted subbasally to medially; first flagellomere slightly (Fig. 5) to considerably elongate (Fig. 6), length rarely less than 1.5 times width but sometimes exceeding seven times width; scape and pedicel sometimes also slightly elongate. Frons setulose with ocellar triangle bare and elongate (sometimes attaining anterior margin); ocelli slightly shifted anteriorly, divided from postocellar by setulose patch. Face usually with angled ventral plate impressed with slight to deep transverse striations; facial plate most distinct and projecting in Chylizinae (Fig. 3), sometimes short to absent in Psila (Fig. 18) and absent in Loxocera (Fig. 8), but transverse striations still faintly evident; face gradually or abruptly receding ventrally in Psilinae, making head subtriangular in lateral view (Fig. 17). Clypeus well-developed, nearly flat and plate like with anterior margin truncated or with medial emargination; palpus varying from small and subcylindrical to large and laterally compressed; labium with short setulae densely to sparsely arranged or restricted to ventral margin.

Thorax. Katatergite slightly (Psilinae; Fig. 17), modestly (Electrochyliza, Belobackenbardiinae; Fig. 12) or strongly (Chylizinae; Fig. 5) bulging. Precoxal bridge absent; postmetacoxal bridge absent or present (Chylizinae). Prosternum small, weakly sclerotized and bilobed, with narrow, lightly sclerotized strip running anterior to sclerites; posterior surface raised. Spiracles subcircular, setulose; posterior spiracle angled dorsally; one or two grooves extending ventrally from anterior spiracle, sometimes ending in a pit. Metanotum with small, laterally directed dorsolateral lobes meeting abdomen.

Wing. (Figs 395–398) Clear to lightly infuscated or with slight patterning, often along veins. Anal lobe and alula well-developed, sometimes slightly reduced. Cell br narrowed on distal section; costa with subcostal break; subcosta usually continuing to costa at near right angle as hyaline weakening in membrane, and sc cell past this break elongate and usually at least faintly arched, but strongly bulging in Chylizinae (less pronounced than state seen in Opomyzidae); in Belobackenbardia (Fig. 395), cell sc straight and sharply narrowing apically, and subcostal vein abutting vein R 1 on distal half (perhaps fused), indistinct apically where it is only distinct as hyaline weakening cutting across much shallower sc cell. Veins R 4+5 and M 1 subparallel; M 1 strongly arched in some Psilinae (Figs 7, 398). Cells bm and cu p reaching, or nearly reaching, level of apex of R s, with cell cu a slightly (Psilinae) to substantially (Chylizinae) shorter. Vein CuA straight. M 4 and CuA+CuP not reaching wing margin. Upper calypter with hairs long to moderate in length.

Legs. Hind femur of Loxocera usually with patch of ventral subapical pile, Chylizinae usually with small, microtrichose ovate pit.

Abdomen. Tergites and sternites separate, sternites not narrowed. Setae pronounced posterolaterally on tergites. Sternite 1 bare or nearly so. Spiracles 1–7 in membrane, 7 th embedded in tergite in Belobackenbardiinae; 7 th spiracle sometimes absent in male.

Male genitalia. (Figs 19 –39) S6 separate, symmetrical, sometimes with posteromedial emargination that may nearly divide sclerite. S8 dorsal, sometimes bare, reduced (Psilinae) to absent (Belobackenbardiinae, Chylizinae); sometimes fused to T6; sometimes with additional vestiges laterally that (in part) may represent S7 (posi- tioned left laterally in other families). Epandrium and surstylus largely immobile, strongly secured to membrane laterally. Epandrium broad, shallow. Cerci simple, sometimes fused. Surstylus present or absent (Psilinae). Subepandrial sclerite absent (Chylizinae, some Psilinae) or composed of two flat, separate lobes (large and basally confluent in Belobackenbardiinae). Hypandrium well-developed, with several medial setae (except Belobackenbardiinae); sometimes with posterolateral apodeme (Chylizinae); arms usually fused posterodorsally. Some Psilidae with medial portion of hypandrium removed as floating ventral plate (Figs 33 –34), with phallapodeme assuming its original position to form “phallapodemic plate” (see Figs 38–39); phallapodeme otherwise rod-like, sometimes folded longitudinally (Belobackenbardiinae; Fig. 24), sometimes widened near base (Chylizinae; Fig. 31), sometimes fused to remainder of hypandrium to form broad, flat plate that may be flat, folded, curved, Tshaped or bifurcate (Psilinae; Fig. 38). Pregonite thin and band-like (Chylizinae; Fig. 31) to large and lobe-like (Belobackenbardiinae (Fig. 25), Psilinae (Fig. 38)); sometimes absent. Postgonite absent. Epiphallus absent. Phallus composed of fused basiphallus and distiphallus; shape flat and linear, bifid, pouch-like or globose; sometimes fused to base of phallapodeme. Ejaculatory apodeme very small with duct sometimes extremely widened.

Female genitalia. (Figs 40–46) Membrane between segments 7 and 8 long, narrow, only short and unmodified in Belobackenbardiinae (Figs 41–43). Except for Belobackenbardiinae, segments 8 and 10 narrow, telescoped within segment 7 at rest, with minute longitudinal grooves; these segments usually distinct from each other, with segment 8 longer and sclerites sometimes divided longitudinally; S8 and T8 mostly undifferentiated; Belobackenbardiinae with S8 narrow and T8 high, laterally compressed. Loxocera abdomen variably modified apically, including lateral compression past segment 6. Cerci short, separate to mostly fused, subcylindrical to compressed; sometimes fused to T10; lateral peg-like sensillae absent in Electrochyliza, Belobackenbardiinae and some Psilinae. Internal components weakly sclerotized and unpigmented (base partially so in Belobackenbardiinae on spermatheca (duct?) and accessory glands); Belobackenbardiinae (Fig. 44) with spermathecae and ducts represented by short narrow, basally pigmented tubules, ventral receptacle perhaps represented by cluster of subspherical swellings apically; Chylizinae (Fig. 46) with spermathecae sac-like, distal section of duct wider with basal grooves, and ventral receptacle (or accessory gland?) flagellar with filamentous apical tubule; Psilinae (Fig. 45) genitalia of uncertain homology, with spermathecae perhaps reduced to apical swellings on widened genital chamber, and ventral receptacle not evident.

Variation—Electrochyliza (fossil). Differs from other Psilidae as follows: frons with minute longitudinal wrinkles following angle of ocellar triangle, which does not attain anterior margin; ventral facial plate, semicircular, height ¼ medial width, with two transverse striations; M 1 shallowly arched; longitudinal grooves on ovipositor apparently absent.The following structures could not be observed: thoracic sternites, postabdominal spiracles, surstylus and male and female internal genitalia.