Eulonchus Gerstaecker, 1856

Borkent, Christopher J., Gillung, Jessica P. & Winterton, Shaun L., 2016, Jewelled spider flies of North America: a revision and phylogeny of Eulonchus Gerstaecker (Diptera, Acroceridae), ZooKeys 619, pp. 103-146 : 107-109

Taxon classification Animalia Diptera Acroceridae

Eulonchus Gerstaecker, 1856 Figs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19

Eulonchus Gerstaecker, 1856: 359

References.

Westwood 1876: 517 (generic checklist); Williston 1888: 40 (key), 1896: 71 (key), 1908: 185 (key); Bigot 1890: 315 (key); Coquillett 1910: 541 (type checklist); Cole 1919: 31 (description, key); Sabrosky 1948 (revision, key); Paramonov 1955: 20 (comments); Schlinger 1960 (revision), 1966: 112 (distribution), 1981: 583 (key), 1987 (host records); Coyle and Icenogle 1994 (host records); Poole 1996: 36 (checklist).

Type species.

Eulonchus smaragdinus Gerstaecker, 1856 by monotypy.

Common name.

North American jewelled spider flies.

Diagnosis.

Eulonchus can be immediately identified from other Panopinae in the New World by the presence of elongate mouthparts, metallic colouration, and pilose eyes. The only other genus in the New World with metallic colouration is Lasia , which is distinguished from Eulonchus in the eyes being separated below the antennae, and in lacking the palpus and alula. Eulonchus is remarkably similar to the endemic New Zealand genus Apsona and is distinguished from it by the presence of tibial spines (lacking in Apsona ), the wing medial veins reaching the wing margin (attenuated in Apsona ) and the antennae placed in the middle of the frons (higher in Apsona ).

Description.

Body length: 7.2-12.8 mm; wing length: 5.2-12.6 mm. Body colouration metallic green, blue or purple, rarely non-metallic (likely due to poor preservation or collection methods). Head hemispherical, width slightly smaller than thorax width; ocellar tubercle slightly to strongly raised, shape variable and either rounded, bifid or trifid, two or three ocelli present; postocular ridge and occiput rounded; eye densely pilose, setae relatively long (2x pedicel length), posterior margin of eye rounded (i.e. not emarginate); antenna located on middle of frons; eye contiguous above and below antennal base; palpus present; proboscis length greater than head length; antennal flagellum elongate, cylindrical to laterally compressed, slightly to strongly tapered apically; in western species male flagellum cylindrical, broader distally, female flagellum more tapered distally; flagellum apex with or without terminal setae; scapes separate (i.e. not fused medially). Thorax with postpronotal lobes not enlarged or contiguous medially; antenotum narrow; subscutellum barely visible beneath scutellum; legs not greatly elongated; tibial spines present apically; pulvilli present; wing hyaline, markings absent; costal vein circumambient around wing, costal margin straight along entire length, rounded apically; humeral crossvein present; vein R1 not inflated distally; R4 and R5 present as forked petiolate veins; radial veins curved towards wing anterior margin; crossvein 2r-m present between M1 and R4+5, bisecting cell r4+5; R4 with or without spur vein; veins M1, M2 and M3 present and reaching wing margin; discal cell closed completely; M4 joining M3, cell m3 petiolate; CuA fused to CuP before wing margin, cell CuA petiolate; wing microtrichia absent; anal lobe well developed; alula weakly developed; abdominal tergites smooth, rounded. Abdomen shape conical to turbinate. Male genitalia (Figs 17-19). Cerci smooth, densely pilose; dorsal surface of epandrium covered with dense, long pile, posterior margin of epandrium usually concave (straight in Eulonchus marialiciae and Eulonchus smaragdinus ); gonocoxite variable in shape and size, with distal apex thinned; aedeagus broad at apex (slightly thinned in Eulonchus halli ).

Included species.

Eulonchus halli Schlinger, 1960: 418; Eulonchus marginatus Osten Sacken, 1877: 277; Eulonchus marialiciae Brimley, 1925: 77; Eulonchus sapphirinus Osten Sacken, 1877: 276; Eulonchus smaragdinus Gerstaecker, 1856: 360 (including Eulonchus smaragdinus smaragdinus Gerstaecker, 1856 and Eulonchus smaragdinus pilosus Schlinger, 1960); Eulonchus tristis Loew, 1872: 60.

Distribution

(Fig. 20). Eulonchus is distributed throughout the Nearctic, with Eulonchus marialiciae found in the eastern state of North Carolina and the remaining species distributed throughout the USA west of the Rocky Mountains, northwards to Canada and south to Baja California, Mexico (Fig. 20). There is significant overlap in the distribution of species of Eulonchus with that of the host (or presumed host) spiders in the families Antrodiaetidae ( Aliatypus sp., Antrodiaetus riversi Cambridge, Antrodiaetus unicolor Hentz) and Euctenizidae ( Aptostichus stanfordianus Smith) (Fig. 21) ( Schlinger 1987), with the range of Eulonchus being clearly inside the range of its hosts. Antrodiaetidae comprise two genera, Aliatypus Smith, and Antrodiaetus Ausserer, with a disjunct distribution in Japan and North America ( Coyle 1971; Hendrixson and Bond 2006). Nearctic antrodiaetids inhabit three primary geographic regions: the deciduous forests of the eastern United States (USA), the forested 'sky islands’ of the southwestern USA, and various habitats throughout the northwestern USA and adjacent portions of southwestern Canada ( Hendrixson and Bond 2006). The euctenizid genus Aptostichus Simon is a genus of trapdoor spiders found predominantly in southern California; Aptostichus stanfordianus is commonly called the Stanford Hills Trapdoor Spider, and is distributed throughout California ( Bond 2012).

Conservation.

Most species of Eulonchus are relatively widely distributed, and locally abundant, except the sole eastern North American species Eulonchus marialiciae . This species is known from only a few specimens, all found within a small contiguous area in the Great Smoky Mountains, with collections from Haywood, Jackson, Macon, Transylvania, and Swain counties in North Carolina. Even though the spider host and floral food source of Eulonchus marialiciae are distributed over much of western North Carolina, southwestern Virginia, and eastern Tennessee, the species is only found in five mountainous counties of western North Carolina, at elevations of 1250m or higher. Considering the apparent limited and very isolated distribution of this species, the conservation status of Eulonchus marialiciae should be further evaluated. Future studies should focus on identifying potential extralimital populations of this species outside of the presently known distribution, as well as understanding potential biotic (e.g. spider host and plant food source range and distribution) and abiotic (e.g. elevation, climate, vegetation and soil type) factors associated with the apparent limited distribution of this species.

Biology.

Adult Eulonchus are locally abundant on flowers ( Cole 1919; Schlinger 1960) and exhibit behaviours that show constancy to particular plant species ( Borkent and Schlinger 2008a, b). Thus, North American jewelled spider flies may form a large and important component of the pollinator fauna for some plant species. Eulonchus visit species from more than 30 plant families (see Table 2), and in multiple habitats ( Borkent and Schlinger 2008a, b). However, the ability of Eulonchus species to serve as pollinators needs to be further studied.

Coyle (1971) reported a large aggregation of Eulonchus marialiciae forming as he was excavating burrows of Antrodiaetus unicolor in North Carolina. A relatively large number of flies (~12 individuals) approached very quickly, hovering close to the ground where the burrows were being excavated, apparently attracted by some chemical released during the process. The author observed multiple adults hovering over and landing near closed burrow entrances. As mentioned above, one of us (C. Borkent) has observed that the newly hatched first instar acrocerid larvae actively search for their hosts, rearing up in search of a spider. Once successful they subsequently penetrate their cuticle and develop as an endoparasitoid ( Schlinger 1987). Additionally, Coyle (1971) observed several instances in which the larva, after feeding on the spider in the bottom end of the burrow, climbed up the burrow wall, attached somewhere above the bottom end and completed development within the burrow.

Comments.

Species of Eulonchus are very similar to species of Lasia and Apsona , and these three genera, as wells as some species of Panops , are commonly known as jewelled spider flies due to their metallic body colouration. Eulonchus species are commonly called Emeralds or Sapphires, depending on the body colour. Winterton (2012) described the thoracic pile in the Australian genus Panops as being reflective, thus brighter when the individual was viewed anteriorly, a characteristic of many Old World panopine species. This character is absent in Eulonchus and most New World panopine genera, with the thoracic pile being of similar brightness regardless of which angle it is viewed. Phylogenetic relationships among Panopinae genera are still poorly known. Based on DNA sequence data, Winterton et al. (2007) found Eulonchus to be placed between Lasia and more derived genera such as Ocnaea , Archipialea , and Arrhynchus .

Phylogenetic relationships

(Fig. 22). The phylogeny performed in this study is based on DNA sequence data and includes five of the six species of Eulonchus . The parsimony analysis resulted in a single most parsimonious tree with length = 904, consistency index (CI) = 0.92, and retention index (RI) = 0.62. The eastern species Eulonchus marialiciae (Fig. 6) and the northwestern Eulonchus sapphirinus (Figs 8-9) were recovered as sister taxa in a clade that is sister to the remaining species of the genus. Even though the support for the branch was low (Fig. 22) we are confident in this relationship as Eulonchus marialiciae and Eulonchus sapphirinus share multiple characters, such as the ovate epandrium (which is thinner at the apex; Fig. 18 C–D), the gonocoxite taller than wide (Fig. 19 C–D), and the aedeagus broad at the apex and not heavily laterally sclerotized (Fig. 17 C–D). These two species are typically bright metallic green or blue with yellow legs. This feature is shared with some individuals of the highly variable Eulonchus smaragdinus from southern California, USA and Baja California, Mexico. Eulonchus smaragdinus (Figs 10-11) was recovered as an intermediate species that subtends the clade comprising the more northern species, Eulonchus tristis and Eulonchus marginatus . Eulonchus halli was not included in the phylogenetic analysis due to lack of fresh material for DNA extraction. However, placement of the species in the Eulonchus tree was postulated based on morphology (see dashed lines on Fig. 20). We hypothesize that Eulonchus halli is more closely related to Eulonchus smaragdinus based on their bifid ocellar tubercles, epandrium somewhat rectangle shaped and wide at the apex, gonocoxite deeply emarginate along anterior margin, fenestrae lacking (Fig. 19A, E) and aedeagus thin at the apex (Fig. 17A, E). The sister-grouping was already suggested by Schlinger (1960). Eulonchus tristis (Figs 13-14) and Eulonchus marginatus (Figs 3-4) have dark brown coloured legs and a thorax and abdomen with dark metallic to brownish-black colouration. Eulonchus tristis is also a highly morphologically variable species with body colour ranging from metallic light blue (Fig. 14) to dark brown (Fig. 13). These two species share multiple genitalia characters such as a somewhat round epandrium, gonocoxite with anterior margin almost straight, with large fenestrae, and aedeagus heavily sclerotized laterally.

Key to species of Eulonchus