Rhopalomyia protrahenda (De Stefani, 1919) De Stefani, 1919

Skuhrava, Marcela, Massa, Bruno & Cerasa, Giuliano, 2016, Rediscovery and identity of Pumilomyiaprotrahenda De Stefani (Diptera, Cecidomyiidae) in Sicily with redescription and reassessment of its taxonomic position, ZooKeys 617, pp. 129-137 : 130-133

Taxon classification Animalia Diptera Cecidomyiidae

Rhopalomyia protrahenda (De Stefani, 1919) comb. n.

Pumilomyia protrahenda De Stefani 1919: 72.

Pulmilomyia artemisiae De Stefani 1929: 262.

Pumilomyia artemisiae De Stefani 1929: 263, 264.

Redescription.

Female (Figs 1-4, 7-9, 12, 14-17). Body size: 1.8-2.2 mm; wing length 1.6-1.8 mm; wing width 0.68-0.70 mm. Freshly emerged females have head and thorax brown and abdomen orange–reddish. Head with large holoptic eyes, eye bridge about 5 ommatidia long at vertex. Ommatidia relatively small and do not touch. Mouthparts extremely reduced. Frontoclypeus with 18-20 setae. Palpus consists of one short, elliptical segment covered with microtrichia. Antennae: scape obconical, pedicel globular, usually 12 flagellomeres, 1st and 2nd connate, ovoid, without necks, densely covered with microtrichia, each with several long setae; of seven females, five had 12 and two 13 flagellomeres, in accordance with information in De Stefani (1919), who reported that about one third of the females had 13 flagellomeres. Flagellomeres gradually decrease in size to end of antenna; circumfila poorly visible, comprising two transverse and one longitudinal band.

Thorax. Wing with R5 joining costa at wing apex, well visible only in basal two thirds; Cu barely visible; anterior wing margin with shorter setae, posterior wing margin with long setae; wing surface covered with short setae. Legs long, covered with short hairs. All legs with simple claws, empodia as long as claws.

Abdomen: Second to sixth segments broad, seventh segment narrow; 8th tergite entire. Ovipositor protrusible, cerci fused, ovoid, setose and setulose; hypoproct small, rounded, setulose, visible only in dorsoventral view.

Male (Figs 5, 6, 11, 13, 18-19). Body size: 1.7-1.9 mm; wing length 1.7-1.9 mm; wing width 0.75-0.80 mm.

Antennae: scape obconical, pedicel globular, usually 13 flagellomeres, 1st and 2nd connate; each flagellomere composed of basal node and distal neck; neck about one half of node. Of three males, one male had 12 and two males had 13 flagellomeres.

Terminalia: gonocoxites thick, completely setulose, with several long setae; gonostyli ovoid, short and thick, completely setulose, covered with setae, at the tip with large, brown, beak–formed curved tooth; cerci broad, lobes rounded, deeply separated, setulose; hypoproct slender, incised; mediobasal lobes setulose, apically with several long setae; aedeagus rounded at tip, as long as cerci.

Other morphological characters as in female.

Larva. Body size: 1.2-1.8 mm long, 0.39-0.55 mm broad, cream colored; integument covered densely with very small spiculae; without spatula sternalis, without apparent papillae on ninth abdominal segment.

Pupa (Figs 10, 27, 28). Body size: 1.5-2.2 mm long, 0.6-0.9 mm broad; head and thorax brown, abdomen orange-red, integument with very small spiculae. An tennal horns small, dark brown; cephalic papillae bulbous with short setae, face with one small horn; prothoracic spiracle small, in the form of a small bulb. Pupal exuviae hyaline.

Biology

(Figs 20-26, 29). Larvae cause small galls on leaves, leaf stalks and stems of Artemisia arborescens . The galls are small hypertrophies of various forms. Only one larva develops in each gall. If galls are abundant, they may cause considerable damage (stunting) of the whole host plant. Larvae pupate in the galls. Several overlapping generations develop per year. New galls may be found on new buds from January onwards, with the emergence of adults until late April and early May. De Stefani (1919) stated that pupae of the last generation use their antennal horns to break out of the gall and drop to the soil, where they remain until the next winter, when the adults emerge. However, his observation is improbable and it is possible that this species diapauses in the larval stage, similar to other Rhopalomyia spp. De Stefani (1919) also stated that females of this species are characterized by high fertility and are able to lay a very high number of eggs on leaves of the host plant; he recorded a mean of 127 eggs per female (78-177) (see also Fig. 21).

Material examined and neotype designation.

The neotype of Rhopalomyia protrahenda is designated here: female, Italy, Sicily, Raffo Rosso, reared from small leaf gall on Artemisia arborescens , 18.III.2008, leg. G. Cerasa, microscope slide number 9571, in the collection of National Museum, Prague, Czech Republic (coll. Marcela Skuhravá).

Other material.

5♀, 3♂, Italy, Sicily, Palermo, locality Raffo Rosso, galls on Artemisia arborescens 3.III.2008, emerged 10-25.III.2008; 3♀, 2♂ same data, emerged 13.II.2012, leg. G. Cerasa; 4♀, 3♂, Italy, Sicily, Cinisi, locality Costa del Furi (Palermo), galls on Artemisia arborescens 11.III.2015, emerged 14-16.III.2015, leg. G. Cerasa; 5♀, 3♂, Italy, Sicily, Palermo, locality Raffo Rosso, galls on Artemisia arborescens 15.II.2016, emerged 16-25.II.2016, leg. G. Cerasa (in ethanol, BMUP); 2♂, 2♀ (neotype included) mounted (on microscope slides in Canada Balsam, coll. Skuhravà, NMPC); 4♂, 13♀, 6 larvae, 10 pupal exuviae (in Hoyer´s medium, NMPC).

Distribution.

The host plant Artemisia arborescens is native to the Mediterranean. It is an erect evergreen perennial, with masses of finely–divided aromatic, silvery–white leaves and single–sided sprays of yellow flowers. The plant occurs from the Iberian Peninsula to Israel, the Italian Peninsula, Sicily, the Balkan Peninsula, Turkey and North Africa, and is naturalized in France. Rhopalomyia protrahenda has been found only in Sicily.

Taxonomic position.

Detailed study of morphological characters of larvae, pupae and adults obtained from galls on Artemisia arborescens , found not far from the type locality in Palermo where De Stefani collected galls in the past, revealed that the causer of these galls, described as Pumilomyia protrahenda by De Stefani (1919), belongs in the genus Rhopalomyia Rübsaamen 1892, and according to the key to the genera of Cecidomyiidae ( Skuhravá 1997) it belongs to the tribe Rhopalomyiini and not the Asphondyliini . The genus Pumilomyia is therefore synonymized here under Rhopalomyia because none of its morphological characters differentiates it from Rhopalomyia . De Stefani (1919) incorrectly assessed morphological characters of adult gall midges, mainly the number of antennal flagellomeres (12), shape of female flagellomeres and of ovipositor - and placed his new genus Pumilomyia in the Asphondylariae.

The female of Rhopalomyia protrahenda has mostly 12 antennal flagellomeres as is typical for all species of Asphondylia but the female flagellomeres of Rhopalomyia protrahenda are oval and not cylindrical as in females of Asphondylia . The female of Rhopalomyia protrahenda has the terminal part of ovipositor slender ending with soft, fused cerci, not aciculate and strongly sclerotized as in females of Asphondylia .

The genus Rhopalomyia Rübsaamen, 1892 is characterized by the combination of the following characters: reduced mouthparts with 1 or 2 segmented palpi, rarely 3; 12-25 flagellomeres; male flagellomeres with long necks, female flagellomeres with short necks; wing with R5 reaching Costa nearly at wing apex; simple or toothed tarsal claws; male genitalia with stout gonocoxites and short, completely setulose gonostyli, with large claw; mediobasal lobes sheath aedeagus, cerci broad, hypoproct slender; female 8th tergite entire; ovipositor long, soft, not distinctly sclerotized; cerci fused. Larvae of most species do not have a spatula sternalis and their papillae are barely visible; pupae usually have strongly developed antennal horns.

The genus Rhopalomyia includes 267 species worldwide ( Gagné and Jaschhof 2014). Larvae induce galls on stems, buds and leaves of host plants almost exclusively of the family Asteraceae . Galls of the same species often occur on several organs of the same host plant species. Alternation of plant organs is connected with the development of several generations per year (e. g., Rhopalomyia tanaceticola (Karsch 1879) on Tanacetum vulgare and Rhopalomyia millefolii (Loew 1850) on Achillea millefolium ). Pupation takes place inside the galls. Species included in the genus are relatively uniform morphologically and show great reduction in taxonomically useful characters. Dorchin et al. (2009) considered that the best means to distinguish among species remains the morphology and structure of their galls together with the identity of the host plant.

Rhopalomyia is relatively species–rich in central, southeast and western Europe, where it contains 38 species. The number of species decreases markedly towards the south. No species were found in the islands of the Mediterranean Sea (other than Sicily) in the past. It is interesting that Rhopalomyia protrahenda is the only species of the genus Rhopalomyia occurring on a Mediterranean island (Sicily). Many Rhopalomyia species have been found to occur in Central Asia, mainly in Kazakhstan ( Fedotova 2000, Skuhravá and Skuhravý 2010). The tribe Rhopalomyiini , as defined recently by Gagné in Gagné and Jaschhof (2014), includes two genera: the large genus Rhopalomyia with 267 species distributed in all zoogeographic regions and associated mainly with various host plants of the family Asteraceae , and the smaller genus Psectrosema with 26 species associated with host plants of the genus Tamarix ( Tamaricaceae ), occurring only in the Palaearctic Region. Only two species belonging to this tribe occur in Sicily: Rhopalomyia protrahenda ( De Stefani 1919) and Psectrosema tamaricis ( De Stefani 1902), both found in the Botanical Garden of Palermo by the Sicilian entomologist Teodosio De Stefani.