Pegomya maculata

Michelsen, Verner & Ackland, Michael, 2009, The Pegomya maculata species group (Diptera Anthomyiidae) in Europe, with description of a new species, Zootaxa 2315, pp. 51-65 : 52-53

The Pegomya maculata species group

Diagnosis. The following combination of characters may separate males and females of the P. m a c u l a t a species group from other species of Pegomya : Antenna, palpus, thorax and abdomen extensively fuscous brown to fuscous black in ground colour; only femora and tibiae to various extent fuscous yellow to yellow. Orbital and interfrontal setulae absent in male; frontal vitta in female with a pair of fine setulae or bare. Setation on lower part of head dark-coloured. Male hind femur with a comb of very short, erect pv-setae on middle third or basal two-thirds. Male terminalia: Sternite V ( Figs. 1, 2 ) on basal part of posterior lobes with a cluster of coarse inclinate setae, on slender distal part bare; surstylus ( Fig. 3 ) basally with a small wart covered in coarse black cuticular pile; postgonite ( Fig. 5 ) membranized at apex and with a coarse, sigmoid seta inserted subbasally; basiphallus ( Fig. 6 ) longer than distiphallus, on distal part with a posterior hump below overhanging slender epiphallus. Female terminalia ( Fig. 24 ): Oviscapt comparatively short and slender with smooth membranes and slender or robust, stiff setae at hind margins of tergites VI–VIII and sternites VI and VII; sternite VIII pieces bulging, softly sclerotized, densely pilose.

Description. Size. Medium-sized, wing length 4.4–6.7mm.

Male. Colour: Head (except in teneral specimens) wholly dark, greyish to silvery grey dusted; only scape, pedicel and basal part of palpus often fuscous yellow. Thorax dark, covered in ash-grey or brownish grey dusting. Wing base, calypteres and halter with an ochre yellow tinge. Legs fuscous brown to black, except femora and tibiae to a varying extent fuscous yellow to yellow, depending on species and age of specimen. Abdomen dark, covered in dense grey dusting delimiting a narrow mid-dorsal dark stripe but no dark anterior bands on tergites III–V. Postabdomen other than tergite VI sparsely dusted, with a distinct dark shine.

Head: Strongly holoptic; frons on upper part much narrower than diameter of anterior ocellus, with linear, contiguous parafrontalia. Fronto-parafacial angle projected beyond lower facial margin; parafacial narrow, in middle about one-third as wide as postpedicel. Orbital and interfrontal setulae absent; frontals 3–5 pairs on lower two-fifths of frons; vestiture on lower part of head all dark. Gena in profile nearly as wide as postpedicel. Postpedicel about two times as long as wide, nearly reaching facial margin; arista shortpubescent. Mouth parts unremarkable.

Thorax: Presutural acrostichal rows slightly wider apart than their distance from adjacent dorsocentral rows; area between presutural rows with several setulae. Prealar seta a little shorter than posterior notopleural seta. Outer posthumeral seta nearly same size as inner posthumeral seta.

Wings: Vein C bare dorsally, finely setulose ventrally. Lower calypter nearly same size as upper calypter. Legs: Mid femur without av-setae but with longish pv-setae on basal half; hind femur with av-row of setae diminishing in length towards base; pv-row forming a comb of short, erect setae, no longer than depth of femur where situated, occupying middle third or basal two-thirds. Submedian setae on fore tibia 1 ad, 1(–2) pv, on mid tibia 0 av, 1 ad, 1 pd and 2–4 p, and on hind tibia 1 av, 2–3 ad, 2 pd and 0 p/pv.

Abdomen: Depressed, parallel-sided, with thickened postabdomen. Tergites II–V with hind marginal setae but without discal setae; tergite VI bare, exceptionally with 1–4 accessory setulae. Sternite V ( Figs. 1, 2 ): Lateral setae confined to disti-lateral margins of basal plate; posterior lobes basally with a dense cluster of inward-pointing setae, distally completely devoid of setae and setulae. Hypopygium ( Figs. 3, 4 ): Surstyli of complex structure typical for Pegomya , separated by short cerci. Gonites ( Fig. 5 ): Pregonite with three strong posterior setae inserted at mid-length and a weak seta at apex; postgonite with coarse anterior seta arising subbasally. Phallus ( Fig. 6 ): basiphallus with a hump-like projection below overhanging slender epiphallus; distiphallus compact, shorter than basiphallus.

Female. Apart from usual sexual differences deviating from male sex as follows: Broad frontal vitta anteriorly extensively orange or orange-brown. Mid-dorsal dark stripe on abdomen broader and more diffuse. Upper half of parafrontals with three pairs of orbital setae; frontals (2–)3 pairs; frontal vitta bare or with a pair of setulose interfrontals; genal setulae few, in a single row. Postpedicel larger, fully extended to lower facial margin. Palpus unremarkable or distinctly enlarged and apically expanded. Vein C dorsally bare or finely setulose distal to insertion of vein Sc. Mid femur only with a few short pv-setae basally; hind femur with avsetae confined to distal half and without pv-setae.

Oviscapt ( Fig. 24 ) rather short but slender, with smooth membranes; stiff hind-marginal setae present on tergites VI–VIII and sternites VI–VII. Anterior two-thirds of sternites VI and VII membranised; sternite VIII pieces strongly bulging, weakly sclerotized, covered in dense cuticular pile, at hind margin with a few sensilla and 0–1 seta. Epiproct, hypoproct and cerci unremarkable. Three spermathecae ( Fig. 30 ) small, fuscous black.

Biology. Adults are rarely collected. As known from related, mushroom-feeding species of Pegomya , adults of both sexes may feed on honeydew and other substances on foliage of trees and shrubs, while the females from time to time must attend fruit bodies of their host mushrooms in order to lay eggs. Larval hosts are only known for P. maculata , but these belong to a wide range of gilled mushrooms of the families Cortinariaceae , Lactariaceae, Marasmiaceae and Tricholomataceae ( Engel 1916, Hennig 1973b, Hackman & Meinander 1979).

Monophyly and relationships. As pointed out by Griffiths (1984), detailed similarity in most parts of the male and female terminalia leaves no doubt about the monophyly of the Pegomya maculata species group. Especially characteristic are the male sternite V and the female sternite VIII (see ‘Diagnosis’ above for details). Based on similarities in the male gonites Griffiths (op. cit.) considered two Holarctic species, P. pallidoscutellata (Zetterstedt, 1852) and P. sociella ( Stein, 1906) , as very closely related to the P. maculata species group. We agree, but also realize that a cladistic analysis using male and female characters of a broader species sample from the mushroom-feeding section of Pegomya would be desirable in the attempt to attain a more accurate picture of the relationships. Unfortunately, females of many species are still not available for study.

Figures

FIGURES 1 – 7. Pegomya maculata Stein, male (Spain: Lerida: Sorpe, except 7 Finland: Ab: Kuustö). 1. Sternite V. 2. Posterior lobe of sternite V, postero-lateral. 3. Hypopygium, posterior. 4. Ditto, lateral. 5. Gonites, right. 6, 7. Phallus.

FIGURES 24 – 26. Pegomya maculata species group, female oviscapt. 24. P. maculata Stein, flat-mounted (Andorra). 25. Sp. indet. A, flat-mounted (Russia: Karelia: Kivach). 26. Same, intact, distal part in lateral view.

FIGURES 27 – 30. Pegomya maculata species group, female oviscapt. 27. Sp. indet. B, flat-mounted (Russia: Karelia: Kivach). 28. Sp. indet. C, flat-mounted (Finland: N: Pytääh). 29. Same, distal part. 30. Same, spermathecae and ducts.