A New Afrotropical Species of Phytomyza in the Subgenus Ptochomyza (Diptera: Agromyzidae)

ABSTRACT Phytomyza impunita sp. n. is described in the subgenus Ptochomyza Hering. This species is known from a single location in the Republic of South Africa, representing the fifth described species in the subgenus, and the second known Ptochomyza to occur outside of the Palaearctic Region, with P. asparagivora (Spencer) known from southern Europe, Pakistan, Ethiopia and Kenya. The new species is described and figured, and discussed in relation to congeners.


Ptochomyza
Hering is a small subgenus of Agromyzidae that includes four previously described species and one treated here as new. throughout most of its history, Ptochomyza was treated as close to, but separate from, the much larger Phytomyza Fallén. It was included in spencer's (1990) Napomyza group, which was not defined, and included Chromatomyia Hardy, Napomyza Westwood, Phytomyza, Ptochomyza and Pseudonapomza Hendel. the group's concept was expanded and elaborated upon in Dempewolf's (2001) treatment of the family, which included a quantitative analysis utilising morphological characters. Based on the results of his analysis, Dempewolf included Aulagromyza Enderlein and Gymnophytomyza Hendel in the group, which he renamed the Phytomyza group; Pseudonapomyza was not included in the group, not being treated in the analysis. this genus group is best characterised by a costa that extends to vein R 4+5 and "costalisation" of the wing, whereby the radial veins are clustered anteriorly to meet the costa closer to the wing base.
This classification was developed more recently in studies by Scheffer et al. (2007) and Winkler et al. (2009), which utilised molecular data sets in quantitative analyses, and are supportive of Dempewolf's Phytomyza group. the analyses of scheffer et al. (2007) reconstructed the wider evolutionary history of the Agromyzidae, and Winkler et al. (2009) focused on the Phytomyza group, attempting to resolve species relationships and further test generic boundaries with a broader sampling of species. results of the latter study strongly supported a polyphyletic Chromatomyia, and found the lineage containing the type species to be deeply nested within Phytomyza, providing good sup port for its synonymy in the same paper. While support for basal branches in the genus group was relatively weak, and additional study is required, results suggested that Napomyza, Ptochomyza and part of Aulagromyza (the bright yellow A. populicola group) were actually basal lineages in a broader Phytomyza. since Napomyza and Ptochomyza were both well defined and supported as monophyletic, they were main tained as valid, but their treatment as subgenera was based on two factors, the first being that they likely rendered the larger Phytomyza a non-natural, paraphyletic entity. the second was that a broader Phytomyza s.l was more pragmatic and useful, being readily identified by easily viewed external and nongenitalic characters: orbital setulae proclinate, costa only extending to vein R 4+5 , medial vein weak/spectral, and crossvein dm-cu absent or situated basally. While much of the classification of this group remains to be resolved (the position of the A. populicola group being especially relevant). the system of Winkler et al. is very useful, is the best quantitatively supported to date, and aims to structure classification on the criterion of monophyly so as to eliminate artificial entities.
Within Phytomyza, Ptochomyza is characterised by projecting parafacials and orbital plates, stronger costalisation of the radial veins, absence of vein dm-cu, reduced chaetotaxy including a shorter vibrissa and usually only three or four visible dorsocentrals that decrease in height anteriorly, a short bare arista, a simplified phallus (Figs 9, 10) and pale coloration. the scutum is covered with a light greyish pruinosity and has three characteristic brown-to-black stripes that do not reach the posterior margin of the scutum (Figs 1-3), although these may coalesce and sometimes cover the entire scutal surface. the pleuron is usually yellow with at least one dark spot on the katepisternum that does not reach the katepisternal seta. the abdomen is mostly yellow with an illdefined, dorsomedial greybrown stripe.

MAtErIAl AnD MEtHODs
Pinned material was examined from the national Museum Bloemfontein, Bloemfontein, south Africa (BMsA). some paratypes were deposited in the natural History Museum, london, united Kingdom (BMnH), the Canadian national Collection of Insects, Arachnids and nematodes (CnC) and the united states national Museum of natural History, Washington, D.C. (usnM). Other collection acronyms used below are: naturhistorisches Museum Wien, Vienna, Austria (nMW); Museum für naturkunde, Institut für systematische Zoologie, Berlin, Germany (ZMHB). Male genitalia were prepared by macerating the abdomen in lactic acid followed by washing in ethanol. Genitalia are stored in glycerin in microvials pinned with the specimen. terminology follows that of lonsdale (2011), with relevant structures of the male genitalia labelled in the figures provided.

Figs 1-10
Etymology: The specific epithet is Latin for "free", referring to its collection locality in the Free state province of south Africa.
Chaetotaxy: Vibrissa short, difficult to distinguish from one or two stronger anterior genal setae. two ori, two ors; sometimes three ori on one side. Postvertical and ocellar setae approximately as long as ocellar tubercle. One to two irregular rows of proclinate orbital setulae. two notopleural setae, closely spaced on posterior half of notopleuron and nearly equidistant from lateral margin. three dorsocentral setae, strongly decreasing in height anteriorly; sometimes fourth postsutural dorsocentral evident anteriorly. Acrostichal setulae in two to four scattered rows on anterior half of scutum (i.e. anterior to base of third dorsocentral); intra-alar setulae sparse, nearly absent posterior to third dorsocentral.
Coloration: setae black to dark brown. Head yellow in base colour, sometimes light yellow, with face, parafacial, gena and postgena always light yellow to whitish; first flagellomere and mouthparts deeper yellow to orange; clypeus light yellow with lateral arms darker yellowish orange; ocellar tubercle narrowly dark brown with centre paler and posterior region (including base of postvertical) yellow; posterolateral corner of frons with narrow spot extending from eye margin to medial base of inner vertical seta, proceeding posteriorly as thin line to back of head and extending in a straight vertical line to side of foramen; remainder of eye broadly surrounded by yellow; back of head brown with outer margin broadly yellow. scutum yellow with faint greyish tint and with three dark stripes: anteromedial stripe narrow, widening at anterior margin, posteriorly ending at midpoint of scutum, and often faded in region just anterior to transverse suture; paired intraalar stripes long, narrow, dark brown, floating, tapering posteriorly; also with very narrow, faded postsutural supra-alar stripe attaining posterior margin of scutum; postpronotum with light-brown anterior spot reaching base of seta. scutellum yellow with greyish tint. Metanotum yellow with posteroventral corner of katatergite, ventral half of anatergite and mediotergite dark brown. Pleuron mostly yellow with greyish tint; anepisternum with narrow, oblique, brown, illdefined anteromedial to ventromedial stripe, with region anterior to stripe slightly paler; katepisternum paler with dark-brown ventral spot not reaching base of seta; anepimeron with brown to dark-brown stripes on anterior half; meron dark-brown with dorsum yellow. legs yellow with base of coxae brownish; femora sometimes with brownish tint (possibly an artifact of preservation). Wing clear. Calypter margin and hairs brown. Halter yellowish white with apical surface of knob light brown. Abdomen mostly yellow; male with brownish, illdefined dorsomedial stripe from tergite (1) 2-6, sternite 8 entirely yellow, epandrium with very narrow double stripe dorsally; female abdomen similarly yellow with stripe from tergites (1) 2-6, and with oviscape dark brown.
Male genitalia: (Figs 4-10) Epandrium as wide as high, length approximately ⅔ height; dorsomedial region above anus bulging. Cercus small, fingerlike. Surstylus small, fully fused to epandrium, not evident. Phallapodeme (not illustrated) long, dark, rod-like. Hypandrium narrow with small triangular apodeme apically; arms broadly arched; two setae on shallow rounded lobe that is distinct from surrounding membranous area. Postgonite broad and subrectangular with long, tapering base, and darker slightly produced apex; one seta and one empty socket on outer-distal surface. Phallus weakly sclerotised, gracile. Phallophorus small, cylindrical, flanked by one pair of relatively dark, rod-like lateral lobes. Basiphallus consisting mostly of long, narrow, dorsal plate split on distal ⅔; fused to dorsal margin of phallophorus; base with left lateral arm wrapping around venter of shaft. Paraphallus small, lobate, membranous. Hypophallus absent. Mesophallus not evident. Distiphallus nearly as long as basiphallus, curled dorsally and tapered to apex, weakly sclerotised laterally along length. Ejaculatory apodeme with relatively broad base, short stem and broad subtriangular blade with very weak distal margin; sperm sac with one pair of small, irregular subcircular sclerites.
Host preference for the new species cannot be reliably predicted at this point because diets are varied across the subgenus and its sister-group relationships are uncertain. Phytomyza asparagi feeds on Asparagus officinalis (Asparagaceae), mining in the leaves and sometimes the stem. Phytomyza asparagivora similarly feeds on A. officinalis (Dempewolf 2004), but is also known from wild, climbing species, including A. acutifolius l., A. africanus lam., A. falcatus l.and A. stipularis Forssk. (spencer 1990). Phytomyza mayeri is known from Clematis recta (ranunculaceae) with the larva feeding in the stem. the host preference of P. czernyi was established by süss (2002), who reared specimens from leaf mines in Italian Foeniculum Mill. (Apicaeae).
Morphologically, Phytomyza impunita is very similar to other Ptochomyza in many external and male genitalic features, but it differs in a number of ways that allow for confident diagnosis. It is larger than other Ptochomyza (wing length 1.8-2.4 mm, not 1.7 mm or less) with a much more pronounced parafacial, the halter is brownish apically, the first flagellomere is small and slightly angulate (similar to P. czernyi -see Süss (2002: fig. 1)), the anterior genal setae are longer, the distiphallus is relatively long and undivided (Figs 9, 10), the postgonite is unique (Fig. 8), the hypandrium is very slender with an apical point (Fig. 7), and the epandrium has a bulge above the anus (Figs 4, 5) and one pair of very narrow dorsal stripes (entirely yellow in other species). Among the rest of the subgenus, Phytomyza asparagi can be differentiated by usually having only a single notopleural seta medially on the notopleuron, the acrostichal setulae are usually in two rows, the pleuron is yellow with two spots on the katepisternum and meron, and the phallus is a simple membranous tube with a shorter distiphallus than that seen in the new species. Phytomyza asparagivora has an arista similar to the new species and the two notopleural setae are positioned posteriorly (although the posterior seta is positioned far above the anterior seta, not equidistant from the lateral margin of the sclerite), but the acrostichal setulae are only in two sparse rows, the distiphallus is bifid with one pair of minute floating sclerites apically in the membrane, and the pleuron is yellow with spots on the katepisternum and meron; this latter character is also seen in P. asparagi, which may be conspecific (Dempewolf 2004). Phytomyza czernyi (based on spencer (1966)) has a uniformly grey scutum with the stripes sometimes partially evident, the pleuron is mostly dark, there is a wide brown stripe from the back of the head to the eye margin lateral to the vertical setae, the genal setae are absent and the distiphallus is bifid (see Süss (2002: figs 3-6)). Phytomyza mayeri (based on descriptions in spencer (1966) and süss (1977-1978)) has a slightly elongate and rounded first flagellomere with a darker outer surface, no acrostichal setulae (one setula possibly present), a fourth presutural dorsocentral, and partial fusion of the three scutal stripes; the phallus is long and undivided, similar to P. impunita, but the left section of the basiphallus is broken medially.
the list of diagnostic characters and hosts presented here for previously described species is based largely on published descriptions, as well as limited material of Phytomyza asparagi and P. asparagivora, and should not be considered exhaustive. Full revision of the subgenus is recommended following more thorough investigation of the Palaearctic fauna.