Arthroteles Bezzi, 1926

Kerr, Peter H., 2010, 2592, Zootaxa 2592, pp. 1-133 : 81-82

Genus Arthroteles Bezzi

Figs. 6, 45, 70, 91, 117, 128, 138.

Arthroteles Bezzi 1926: 321 . Type-species Arthroteles bombyliiformis Bezzi 1926 , by original designation.

Diagnosis. The most striking autapomorphy for this genus is the elongate, sclerotized proboscis, which is adapted for nectar feeding. At the base of the mouthparts, the cardo is swollen distinctively.

Species of Arthroteles are moderately sized (5 to 7.5 mm) flies of gray to dark gray coloration, having an antenna that bears seven to eight tapering flagellomeres (first flagellomere much larger than all others); eyes in male holoptic (with the exception of A. longipalpus ); laterotergite setose; tibial spur formula 0:2:2; M 3 present; short macrochaetae on all tibiae; female tergite 9 without ventrolateral arms; and female spermathecal ducts without accessory glands. Arthroteles is most similar to Atherimorpha in general form, but may be distinguished from this and all other related flies by the form of its mouthparts. It also differs from Atherimorpha in having hind coxal tubercles and short macrochaetae on all tibia.

Description. Head. Clypeus bulbous, produced anteriorly. Scape approximately same size as or slightly larger than pedicel. Flagellomeres 7–8, cylindrical; first flagellomere larger than other flagellomeres; terminal flagellomere more elongate than flagellomeres of equal girth. Eyes inconspicuously setulose; in male, eyes holoptic or dichoptic (in A. longipalpus only), flattened dorsally, ommatidia evenly distributed, of equal size (in A. longipalpus only) or ommatidia split into dorsal and ventral areas and smaller ventrally. Labella reduced, very short, with few pseudotracheae. Hypopharynx, labium, and labrum very elongate; theca lateral sclerites adjacent, apparently fused with suture. Palpus two-segmented; distal segment longer than proximal segment. Lateral ridge of oral margin absent. Stipes surrounded by membrane above theca, directed posteriorly. Cardo swollen. Lacinia longer than palpus; tip not serrated. Mandibles absent. Cibarial pump long, clearly not as wide as long. Cornu shorter than cibarial pump. Pharyngeal pump narrow along most of length, mostly flat along its length, longer than length of cibarial pump.

Thorax. Mesonotum with vittae. Dorsocentral bristles absent, all dorsal setae of equal length. Anepisternum bare. Laterotergite, katatergite, and anatergite indistinguishable. Laterotergite setose, in rows, mostly on ventral half (katatergite). Proscutellum present. Subscutellum not enlarged nor lengthened; inconspicuous. Wing hyaline or lightly infuscate, without markings. Pterostigma absent. Lower calypter reduced. Upper calypter well developed, with broad curvature, lobe-like, width twice length or less. Costa extends past wing tip (to at least R 5). Humeral crossvein well developed. Sc-r crossvein weakly developed, positioned distal to h by approximate length of h. Dorsal side of R 1 setulose, ventral side bare. All other wing veins without setulae. R 2+3 nearly straight, apical third of R 2+3 ultimately bends slightly anteriorly toward wing tip (although very nearly straight). Length of R 2+3 longer than R 5, but less than twice as long. Base of R 4 –R 5 fork proximal or directly above distal end of cell dm. R 4 at base strongly curved or angled; nearly straight apically. R 4 and R 5 contain wing tip. R 5 clearly longer than R 4+5 (r-m to R 4 origin). M 3 present. Cell m 3 convergent at margin. Origin of CuA 1 at cell bm. CuA 2 about 2/3 length of posterior vein of cell bm. Alula with broad curvature, rounded evenly. Anal lobe well developed. Cell cu p open. Halter knob between 1/3–1/2 length of stem. Tibial spur formula 0:2:2. Hind coxal tubercle present. Hind tibial macrochaetae present, short.

Abdomen. Terminal abdominal segments 5–10 evenly tapered from segments 1–4. In female, tergite 7 much longer than wide, intersegmental membrane between segments 7 and 8 especially long. Sternite 8 length wider than long or as wide as long. Male terminalia with epandrium simple, not containing hypandrium ventrally. Epandrium wider than long, strongly notched anteriorly. Tergite 10 absent. Hypoproct triangular, tomentose, without setae. Cercus base held underneath epandrium, directly adjacent to one another, separation distance one quarter width of cercus or less. Cerci, in posterior view cupped, forming circular outline medially. Hypandrium separated from gonocoxites by complete suture. Gonocoxite with sinuous dorsal ridge, leading to gonocoxal apodeme. Gonocoxal apodemes short or long enough to reach anterior margin of hypandrium. Sperm sac bulbous, with shallowly paired swellings ventrally. Lateral ejaculatory processes present, not part of sperm sac posteriorly. Ejaculatory apodeme moderately long, reaching anterior margin of hypandrium, or long, reaching beyond anterior margin of hypandrium. Ejaculatory apodeme laterally compressed. Aedeagal tines absent. Endoaedeagal process present. Female terminalia with three spermathecae, swollen in shape, lightly sclerotized or not sclerotized. Spermathecal ducts no more than three times length of sternite 9, not inflated at base of spermathecae. Spermathecal duct accessory glands absent. Spermathecal ducts near junction sclerotized, thickened, with surface furrows in rings. Spermathecal duct junction not thickened. Common spermathecal duct thickened, with apical transverse ridge and suture at junction of spermathecal ducts; long, clearly longer than longest diameter of genital chamber. Genital chamber oval, moderately sized. Accessory gland posterior to genital chamber inconspicuous, easily overlooked even after staining. Sternite 9 anterior end pointed; posterior end with broad lateral extensions, joined medially with seam, in vertical plane. Tergite 10 entire, short (length less than half width) (however, elongate in Nagatomi & Iwata 1976). Sternite 10 entire, roughly pentagonal, pointed posteriorly; posterior half below first cercal segment. Cercus two-segmented. First segment of cercus not elongate, with ventral process. Ventral lobes of first segment of cercus not curving ventrally towards one another to form ring. Basal cercal segment adjacent dorsally. Second cercal segment not elongated. Cercus with apical sensory pits.

Larva. Unknown.

Biology. Arthroteles is noteworthy for its specialized flower-feeding behavior, restricted to the mountain ranges of the Western Cape Province and the escarpment in eastern South Africa ( Stuckenberg 1956a). Stuckenberg (1956a) reports that Arthroteles cinerea resembles bombyliids in flight and is most often collected on the flower heads of Helichrysum spp. (Asteraceae) . Interestingly, Arthroteles apparently has species-specific, or nearly species-specific periods of activity. Historically, A. cinerea adults are collected in March, whereas A. bombyliiformis are collected in August or September. Arthroteles orophila is active in November. The flight of A. longipalpis occurs in July, and may overlap to some degree with A. bombyliiformis .

Literature. Illustrations of mouthparts, antenna, wing, male and female genitalia, and dichotomous key to species is given by Stuckenberg (1956a). A new species is illustrated by Nagatomi & Nagatomi (1990a).