Tanytarsus oscillans Johannsen

Cranston, P. S., Ang, Y. C., Heyzer, A., Lim, R. B. H. & Wong, W. H., 2013, The Nuisance Midges (Diptera: Chironomidae) Of Singapore’S Pandan And Bedok Reservoirs, Raffles Bulletin of Zoology 61 (2), pp. 779-793 : 790-791

Tanytarsus oscillans Johannsen

Material examined. — (All slide mounted). Malaysia: Kuala Lumpur, Muzium Negara , pool in grounds, 2 males, 1 Oct.1976, coll. Cranston ( BMNH) . Singapore: Poyan Reservoir, 1°22'33"N, 103°39.16"E, 1L, Oct.2008 ( NUS colonisation experiment); Lower Seletar Reservoir , 1°25'27"N, 103°51.29"E, 9 males, 19 Mar.2009, coll. Cranston; Singapore, Bedok Reservoir, 1°20′47″N, 103°55.31"E, 6 males, 2Pe, 9 Jan.2011, coll. Ang; same location, 6Pe, 23 Feb.2012, coll. Ang; same location and date, 3 P ♂, 1Pe, coll. Cranston; same location, ex-rearing, 5L, 1L(P), 1Le(P), 5P ♀, 2P ♂, 31 Oct.2012, coll. Woodford. Deposited ANIC, ZRC . Molecular vouchers (all coll. TMSI, unless stated): CP5, ♂, Pandan reservoir, between points 4 and 5, 4 Jul.2012; CP8, ♂, Bedok Reservoir , Floating deck A, 2 Jul.2012; CP14, ♂, Upper Seletar Reservoir , Fishing area , 15 Aug.2012; CP54, ♂, Bedok Reservoir , Floating deck A, 23 Oct.2012; CP58, 62, 65, 66, 177, ♂♂, Upper Seletar Reservoir , Fishing area , 12 Sep.2012; CGBED1 , ♂, Bedok, ‘ Waterfront Key’ condominium balcony, 1 Dec.2012, coll. Gerald Lui; CP115, 121, 128, 130, Larvae, Upper Seletar Reservoir, Fishing area , 26 Sep.2012; Deposited ZRC .

Description. — Adult. The adult male was described in detail, accompanied by line drawings of genitalic features, by Ekrem (2002). We provide photographs of the male habitus ( Fig. 26 ), genitalia ( Figs. 27–30 ) and female ( Fig. 10 ).

Pupa (n=10) (all measurements in μm, unless stated).

Body length 3.0–3.3 mm, cephalothorax length 1.0–1.3 mm. Cephalic area without tubercle or warts, frontal seta ( Fig. 31 ) 35–38. Thoracic horn hyaline, straight and tapering with sparse bristle-like short setae, 300–335 long. Nose ( Fig. 32 )

well developed, visibly containing many fringe setae of the pharate adult wing.

Abdomen ( Fig. 16 ) with D and V setae normal for the genus, none taeniate or especially strongly developed: L-setae of T (tergites) II–VI non-taeniate, VII with 3 nontaeniate and 1 (rarely 2) taeniate L-setae, VIII with 5 taeniate L-setae. TI bare; TII with elongate spinule bands extending from somewhat transverse area for tergite length, with bare median area; TIII with band of long spines commencing more anterior than site of D1 seta, anteriorly without fine spinules; TIV with anterior patches of mixed short spines and spinules, located alongside D1 seta; TV & TVI with anterior patches of fine spinules; TVII and TVIII without spinules. Hook row on posterior of TII with 30–35 hooks extending 15–18% of segment width. Posterolateral ‘comb’ of segment VIII with 5–7 larger marginal spines and 9–12 submarginal smaller spinules ( Figs.35, 36 ). Anal lobe with 27–31 taeniae and 2 dorsal setae. Genital sacs of males extend slightly beyond anal lobe apex, those of females shorter.

Pupal exuviae sexually dimorphic with long spines of TII in female shorter, fewer and paler (cf. Figs. 33 and 34 , same scale), and with fewer stronger spines in posterolateral comb (cf. Figs. 35 and 36 , same scale).

Larva (all measurements in μm unless stated):

Body length 2.0–2.25 mm, body pale green in 4 th instar.

Head capsule. Length 260–280, light golden with pale occipital margin except pale brown ventrally, as is postmentum; mental and mandibular teeth golden brown ( Figs. 37, 39 ). Cephalic setae S3 simple ( Fig. 40 ). Antennal pedicel rounded, lacking spur. Antenna plus Lauterborn organ stems 99–102% length of head ( Fig. 39 ). Antennal segment lengths 104–120, 37–45, 13–17, 7–8, 1–1.5. Antenna ratio 1.6–1.8. Lauterborn organ stems 120–130, with organs scarcely wider than stem, 8–10 long. Second antennal segment with incomplete pigmentation: basal sclerotised portion 50–60% of total length (some specimens with unpigmented 2 nd antennal segment including asymmetry between sides). Mentum ( Fig. 42 ) 67–70 wide, brown, with paler median triple tooth; ventromental plates 68–78 wide.

Body. Anterior parapods claws all yellow, simple, fine. Thoracic setation simple. Each abdominal segment bearing a bifid, plumose seta, 210–225 long, in the l 4 position on the postero-lateral of the segment. Abdominal segment 7 with paired lateral ‘tubules’ of length 25–30 ( Fig. 38 ). Procercus bearing 7–8 anal setae of maximum length 350–360. Anal tubules short, squat, 100–120 long ( Fig. 39 ). Posterior parapod claws all simple and robust, golden-yellow.

Comments. — The adult male of T. oscillans is recognised by the features stated by Ekrem (2012) mainly deriving from the genitalia in which the anal tergite bands are separate and nearly reach the anal point crests, with 2 median setae and small microtrichiose area medially; anal point with 4–6 large spinulae between crests with extensive microtrichiae between crests; oval superior volsella, finger-like digitus extending to near or slightly beyond apex of superior volsella and median volsella short, with foliate and setose lamellae orientated medially. The closest species (92%) in barcoding databases, Tanytarsus kiseogi described from Korea by Ree & Jeong (2010), is based on the adult alone. The uniform yellow thorax and Antennal Ratio of 1.0–1.2 are shared. The male hypopygium of T. kiseogi , as described and drawn, differs from T. oscillans only subtly including in the ‘pinched’ superior volsella and shorter digitus. The presence of microtrichiae between the crests of the anal point cannot be determined. Adults were collected beside a river but the immature stages to verify the habitat, and assist in taxonomy remain unknown.

The pupa of T. oscillans is distinctive by virtue of the pattern of tergal spines and spinules patterns. The pupa of T. oscillans resembles, and coexists in standing waters in Singapore with, T. formosanus Kieffer but can be distinguished by the near bare thoracic horn, minute frontal setae, different patterns on tergites including the continuous but sparser longitudinal spinule rows on TII, spines of TII commencing more anteriorly (rather than mid-segment), without spinule patches anterior to longitudinal spine rows on TIV. From the Australian pupal type ‘B2’ distinguished by the very short frontal setae, narrower hook row and reduced spinulation on TII, few spinules anterior to the long rows of spines on T IV, the fewer spines in patches on T IV and V, the location and number of taeniate setae on segment VII.

The larva possesses tubules which can be seen at low magnification ( Fig. 38 ) on the lateral penultimate abdominal segment. Such structures are reported previously in larvae of this genus only from Tanytarsus dibranchius Kieffer in Zavřel ( Spies, 1998) from western Europe, and by Dejoux (1968) for T. nigrocinctus Freeman from Chad. This latter taxon is now treated as a junior synonym of the more widespread (including Malaysia and Singapore) Tanytarsus formosanus Kieffer ; however, larval tubules have not been reported since from regional specimens, and the significance in identification is unclear. Whatever, T. formosanus differs amongst other features in the antenna, with Lauterborn organs no more distal than the antennal apex. Many regional (Australasian) larval Tanytarsus have antennae + Lauterborn organs as long (or even longer) than those of T. oscillans , and thus the feature, although distinctive, is not characteristic.

Variation includes sexual dimorphism of the pupa—both in strength and intensity of pigment of the spines on TIII ( Figs. 33, 34 ) and the number and size of the spines of the posterolateral ‘comb’ of segment VIII ( Figs. 35, 36 ). Such sexual dimorphism, known in some other Tanytarsiini , must be taken into account in segregating pupal exuviae collected in routine surveillance/monitoring.

Figures

Figs. 26–30. Midges as nuisance in Singapore. Tanytarsus oscillans male: 26, habitus; 27, hypopygium, dorsal; 28, anal point, dorsal, detail; 29, superior volsella, dorsal, detail; 30, superior and median volsella, dorsal, detail. Abbreviations: apt, anal point; atb, anal tergite band; cr, anal crest; gc, gonocoxite; gs, gonostylus; iv, inferior volsella; mv, median volsella; sv, superior volsella.

Figs. 6–11. Midges as nuisance in Singapore. Polypedilum nubifer female: 6, habitus, lateral, 7, habitus dorsal. P. nubifer eggs: 8, Egg masses; 9, solitary egg mass. Tanytarsus oscillans: 10, female habitus lateral; 11, eggs.

Figs. 31–36. Midges as nuisance in Singapore. Tanytarsus oscillans pupa: 31, frons; 32, nose of wing sheath; 33, tergite III of female; 34, tergite III of male; 35, posterolateral tergite VIII of female; 36, posterolateral tergite VIII of male. Abbreviations: fr, frontal setae; S, sternite (VIII=8th); T, tergite (III=3rd).

Figs. 12–16. Midges as nuisance in Singapore. Polypedilum nubifer pupa: 12, dorsal tergites; 13, frons; 14, base of thoracic horn, 15, posterolateral of tergite VIII. Tanytarsus oscillans pupa: 16, dorsal tergites.

Figs. 37–42. Midges as nuisance in Singapore. Tanytarsus oscillans larva: 37, lateral head, 38, posterior abdomen; 39, dorsal head; 40, dorsal view of head, antennal bases, S3 setae; 41, antenna; 42, mentum.Abbreviations: LO, Lauterborn organ; S3, cephalic seta; m, mentum; vmp, ventromental plate.