INTRODUCTION

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 R4+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 support 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 maintained 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 non-genitalic characters: orbital setulae proclinate, costa only extending to vein R₄₊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 grey-brown 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.

TAXONOMY

DISCUSSION

Phytomyza impunita is so far known from only a single locality in South Africa. All previously described Ptochomyza are European in distribution, at least in part. Phytomyza czernyi Strobl is known from Croatia, Italy and Malta (Cerný 2004). Type data are as follows: CROATIA: Volosca (HT ♂, coll. Strobl) (Strobl 1909). Süss (2002) photographed and illustrated the larva and adult. Phytomyza mayeri (Spencer) is known from Spain (von Tschirnhaus, pers. comm.), Austria, Croatia and Italy. Type data are as follows: AUSTRIA: Vienna, Eichkogel, ex stem of Clematis recta, em. 21.iii.1953, H. Mayer (HT ♀ NMW). It was discussed in Hering (1958) as Phytomyza czernyi, Hering (1967) illustrated the mine and larval spiracles, and Süss (1977–1978) illustrated the adult. Phytomyza asparagi (Hering, 1942) is known from Spain, Greece (von Tschirnhaus, pers. comm.), Germany, Lithuania and Palaearctic China. Type data are as follows: GERMANY: Zinna near Jüterbog, ex mine on Asparagus officinalis L., 29.viii.1941, H. Buhr (ST ♂♀ ZMHB). This species was further discussed in Spencer (1990) and Ostrauskas et al. (2005). Phytomyza asparagivora (Spencer) is known from southern Europe, Pakistan and Africa, including the Canary Islands (von Tschirnhaus, pers. comm.), but unlike the South African P. impunita, this species has only been recovered in the Afrotropics as far south as Ethiopia and Kenya. Type data are: ETHIOPIA: Addis Ababa, Little Akaki River, 2300 m, bred ex leaf-mines in Asparagus africanus Lam. [det. J.B. Gillett], 31.x.1959, E.M. Hering (HT ♂ BMNH). This species was discussed in Spencer (1964, 1973, 1985, 1990).

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).

Figs 1–10.

Phytomyza (Ptochomyza) impunita sp. n., photos: (1) female paratype, left lateral; (2) male holotype, dorsal; (3) same, left lateral. Figs 4–10: P. impunita paratype, male genitalia: (4) epandrium, posterior; (5) epandrium, left lateral; (6) sperm pump; (7) hypandrium, ventral; (8) left postgonite, left lateral; (9) phallus, left lateral; (10) phallus, ventral.

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.