Pegomya fulgens

Michelsen, Verner, 2015, Taxonomic review of the major larval pests of bolete fungi (Boletaceae) in Europe: The Pegomya fulgens, furva and tabida species groups (Diptera: Anthomyiidae), Zootaxa 4020 (1), pp. 51-80 : 52-54

The Pegomya fulgens subsection

Diagnosis. Ground colour of head, body and appendages ranging from extensively yellow to extensively brownish black. Even the darkest males of Pegomya furva are yellowish enlightened at palpal base and on tibiae, and the palest, newly emerged males and females show at least some darkening on occiput and postpedicel. Prementum glossy, without any dusting. Knob of haltere yellow. Antennae and mouth parts unremarkable: Postpedicel more or less shorter than distance between upper katepisternal setae; palp at widest point not or barely exceeding width of parafacial. Male frons at narrowest point with contiguous parafrontalia usually separating the eyes by less than transverse diameter of anterior ocellus, bare apart from 2‒4 pairs of frontal setae on lower half. Female frons with pair of interfrontal setae varying in size from normal to absent. Parafacialia moderately narrow, in middle one-third to two-thirds as wide as postpedicel. Genal setae few, standing in a single row. Acrostichal setal rows in front of suture usually slightly closer together than their distance to adjacent dorsocentral setal rows. Prealar seta, except in P. vittigera , shorter than posterior notopleural seta. Lower calypter same size as or slightly smaller than upper calypter. Vein C, except in P. vittigera , without d setulae but with abundant v setulae. Fore tibia with 1 ad and 1 p setae. Mid femur with 0 av and 2‒4 basal pv setae (fewer in females than males). Mid tibia with 0‒1 ad (present and stronger in females), 1‒2 pd and 1‒2 p setae. Hind femur ( Fig. 6 ) with 4‒8 av setae, 0‒ 1 v seta near at base and 0‒3 pv setae at mid-length. Hind tibia with 1 av, 2‒3 ad and 2 pd setae. Female tergite VI shiny, without dusting, normally almost concealed under tergite V. Three spermathecae blackish, small and globular.

Species groups and relationships. The Pegomya fulgens subsection was first proposed by Griffiths (1983) for three “superspecies” referred to in the following as the Pegomya fulgens , furva and tabida species groups. The Pegomya fulgens species group includes two very similar species, the West Palearctic P. f ulgens (Meigen) and the northern Holarctic P. trangressa (Zetterstedt) . The Pegomya furva species group consists also of two weakly differentiated species, both with northern Holarctic distributions, P. f urva Ringdahl and P. circumpolaris Ackland & Griffiths. The Pegomya tabida species group contains 11 species, among them six Holarctic: P. z o na t a (Zetterstedt), P. notabilis (Zetterstedt) , P. tabida (Meigen) , P. vittigera (Zetterstedt) , P. i n ci s i v a Stein and P. scapularis (Zetterstedt) , two Nearctic: P. crassiforceps Griffiths and P. gilvoides Griffiths , and three Palearctic: P. tenera (Zetterstedt) , P. pulchripes (Loew) and P. ringdahli sp. nov. All nine species of the Pegomya tabida species group with Holarctic or Palearctic distributions are found in Europe. The knowledge about the occurrence of the Pegomya fulgens subsection east of the Urals is still fragmentary. The only species recorded from China are P. tabida and P. pulchripes ; from Japan P. zonata , P. notabilis , P. pulchripes and possibly P. ringdahli ; from Korea P. pulchripes ; from Far East Russia (Kamchatka, Sakhalin, Kuriles) P. transgressa , P. notabilis , P. incisiva and P. pulchripes .

The evidence for the monophyly of the Pegomya fulgens subsection is rather circumstantial, but supported by the observation that the Pegomya furva species group perfectly bridges the morphological gap between the Pegomya fulgens species group and the overall apomorphic Pegomya tabida species group. Further support is gained from the observation that the larvae from the three species groups may all feed exclusively on a narrow selection of bolete sporocarps.

The Pegomya fulgens species group appears overall plesiomorphic in relation to the closely related Pegomya furva species group, notably in respect to the simpler male sternite V and the average length oviscapt. Still, it is conceivably monophyletic considering that only subtle morphological differences exist between the only two included species.

The Pegomya furva species group also contains two weakly differentiated species. Their monophyly is well supported by the male sternite V possessing a prominent outer expansion on the posterior lobes, and by the very short oviscapt.

The Pegomya tabida species group, presently including 11 species, is well supported as monophyletic based on several characters of the male and female terminalia: Posterior lobes of male sternite V split into an obtuse, outer expansion and a projecting inner lamella separated distally by a membranous incision; surstyli and cerci slender and elongated; postgonite and phallus enlarged and elongated; hind marginal setae increasingly reduced on segments VII and VIII of oviscapt; female hypoproct small, without usual cuticular pile.

The structure of the male sternite V in the Pegomya furva species group ( Figs 13‒15 ) approaches that of the Pegomya tabida species group ( Figs 28‒36 ) and suggests that these species groups are most closely related. However, as pointed out by Griffiths (1983), this is in conflict with other and perhaps more convincing evidence for a closest relationship between the Pegomya fulgens and Pegomya furva species groups. This is first of all the dense clothing of sensilla under the mid and hind tarsi in the females of both species groups ( Fig. 5), an obvious apomorphy not known from other Pegomya species. The total absence of scales or other surface texture on the membranous parts of oviscapt may also be synapomorphic for the Pegomya fulgens and P. furva species groups.

Biology. Studies on Diptera breeding in sporocarps of macrofungi undertaken in Finland ( Hackman 1976, 1979, Hackman & Meinander 1979, Ståhls et al. 1989) and in boreal North America ( Griffiths 1983, Bruns 1984) strongly suggest that all 15 species of the Pegomya fulgens subsection have a very narrow larval host range involving primarily boletes (Boletacea) of the genus Leccinum , notably L. scabrum and L. versipelle . A few species have also been reared from Boletus edulis and closely related “porcini boletes”. A few records from other fungi, notably by Dely-Draskovits & Mihályi (1972), are probably based on misidentifications of Pegomya species with different host preferences.

All species appear to be univoltine and overwinter as puparia in the ground. Puparia of some species may hibernate twice in response to dry seasons with a small production of sporocarps. The adult flies emerge by mid- June to mid-July, often weeks before the emergence of the host sporocarps. The females of some species are longlived and capable of laying eggs on late season sporocarps. My own observations in south Sweden indicate that the adults do not normally forage on flowers, but are regularly seen “grazing” on foliage of oak and hazel. They are also attracted to surfaces with secretions from aphids. I have never observed males engaged in swarming or station taking. Gravid females are of course attracted to young sporocarps of Leccinum and Boletus aff. edulis .

Most species deposit their eggs four or five together in the pore layer of the young sporocarp according to Hackman (1979). As noted by the same author, a certain niche partion exists though, as two species with sharp and pointed cerci insert their eggs in bigger masses beneath the cap cuticle ( Pegomya notabilis ) or within the stipe ( P. incisiva ). I would suspect, based on the sharply pointed cerci, that also the female of P. vittigera has a similar egglaying strategy. The larvae hatch from the numerous eggs within a day or two and start vigorously to feed and tunnel their way through all fresh fungal tissue available in an attempt to reach maturity before the decay of the sporocarp has progressed too far.

Species of Leccinum have a circum-boreal, mainly cool-temperate to low arctic distribution that corresponds well with the distribution range of the Pegomya fulgens subsection. Den Bakker & Noordeloos (2005) recognize 16 species of Leccinum in Europe, most of which are establishing mycorrhizal associations with species of either birch ( Betula ), aspen and poplars ( Populus ), pine ( Pinus ) or spruce ( Picea ). The low arctic and alpine zones have species of Leccinum ( L. holopus and L. rotundifoliae ) forming mycorrhizae with scrubs of Betula nana and its Nearctic counterpart, B. glandulosa . This explains the occurrence of species of the Pegomya fulgens subsection in southern Greenland ( Michelsen 2006b) and beyond the tree line in Fennoscandia ( Ringdahl 1951).

Boletus edulus and its close allies, also known as “porcini mushrooms”, are widely distributed in the Northern Hemisphere from the subarctic zone to the tropics with some 25 species ( Dentinger et al. 2010). This commercially important group of boletes includes only four species in Europe according to Beugelsdijk et al. (2008), but some of them reach out to habitats in the Mediterranean Basin well beyond the climatic tolerance of the boreal Pegomya fulgens subsection. They are in northern Europe mainly found in mycorrhizal associations with pine, spruce, oak and beech. Only three species of the Pegomya fulgens subsection (P. z o na t a, P. notabilis and P. scapularis ) have been reared from sporocarps of the Boletus edulis species group ( Hackman & Meinander 1979) in Europe. Bruns (1983) further recorded Pegomya vittigera and Pegomya aff. tabida from sporocarps of Boletus edulis in Minnesota, USA.

Figures

FIGURES 6 ‒ 10. Pegomya spp., male. Left hind leg. Same scale.

FIGURES 11 ‒ 15. Pegomya spp., male. 11 ‒ 13. Sternite V in laterodorsal view. 14, 15. Sternite V in dorsal view. Same scale.

FIGURES 28 ‒ 33. Pegomya spp., male. Sternite V in laterodorsal view. Same scale.

FIGURES 34 ‒ 36. Pegomya spp., male. Sternite V in laterodorsal view. Same scale.