Twinnia japonensis Rubtsov, 1960

Kim, Sam-Kyu, 2020, Two new genera of black flies (Diptera: Simuliidae) of Korea, Journal of Species Research 9 (1), pp. 11-18 : 15-17

Twinnia japonensis Rubtsov, 1960 ( Fig. 3 )

Twinnia nova japonensis Rubtsov, 1960 : Die Fliegen der palaearktischen Region, 14 Simuliidae : 128. Type locality: Japan (Honshu).

Prosimulium novum: Bentinck, 1955 , not Dyar & Shannon.

Prosimulium (Twinnia) japonense: Uemoto, 1980 (revision); Saito et al., 1996 (Japanese record); Uemoto, 2005 (Japanese key and illustrations).

Twinnia japonensis: Saito, 2015 (Japanese list and names); Adler, 2019 (world checklist).

Diagnosis. Larva of T. japonensis can be easily distinguished from other black flies by the following characteristics: labral fan absent; gill histoblast with 16 filaments in [(6 + 2) + (4 + 4)] arrangement; postgenal cleft absent; head with anteromedial and posterolateral head spots absent; posteromedial head spots distinct, extended to the level of eye spot; 7 spots at posterolateral and ventral margin of head capsule; hypostoma with teeth broad, apically rounded; median tooth trifid, shorter than lateral and sublateral teeth; rectal papillae with 3 simple, long, slender lobes.

Description. Larva. Body length 6.6 mm (n = 10). Body ( Fig. 3A ) light brownish grey ground color. Head capsule ( Fig. 3B ) light brown, longer than wide, triangular shaped in dorsal view; moderately covered with pale hairs with dark base ( Fig. 3D ). Cephalic apotome (frontoclypeal apotome) strongly contracted posteriorly ( Fig. 3B ). Head spots ( Fig. 3B-3D ) with first and second anterolateral head spots distinct, well separated; anteromedial and posterolateral spots absent; posteromedial spots distinct, extended anteriorly to the level of eye spot; posterolateral margin of head capsule with 7 spots, 3 large groups of spots and 3 round spots at the area between eye spots and postocciput, single round spot ventrally ( Fig. 3A, 3C ). Labral fan absent. Antenna ( Fig. 3B, 3D ) with proximal and medial article transparent, distal article brown, gradually tapered toward apex; proportional ratio from proximal to distal article as 0.8: 1: 1. Postgenal cleft ( Fig. 3C ) absent. Hypostoma ( Fig. 3E ) with 7 broad, apically rounded teeth; sublateral teeth prominent, bifid; median tooth round, trifid, shortest; lateral tooth longer than median tooth, slender, curved, dull pointed; paralateral tooth well developed, apically pointed; intermediate teeth and lateral serration well developed; Hypostomal seta 3-4 pairs, simple. Subesophageal ganglion ( Fig. 3C ) not pigmented. Prothoracic proleg ( Fig. 3G ) without lateral sclerite. Gill histoblast ( Fig. 3F ) with 16 filaments, arranged as [(6 + 2) + (4 + 4)] from dorsal to ventral, with long stems. Posterior proleg ( Fig. 3H, 3I ) with 10-12 hooks in 58-64 rows. Rectal papillae ( Fig. 3J ) with 3 simple, long, slender lobes. Anal sclerite Y shaped.

Pupa. Unknown from Korea.

Specimens examined. Korea: Gangwon-do , Chuncheon-si, Namsan-myeon, Banghari, 37°47 ʹ 16 ʺ N, 127° 32 ʹ 28 ʺ E, altitude 75 m, 19.iv.2019, SK Kim (4 larvae with 2 ultimate, 2 penultimate); ditto, 24.iv.2019 (28 larvae with 3 ultimate, 11 penultimate, 14 early instars); Gangwon-do, Hongcheon-gun, Bukbang-myeon, Wonso-ri, 37°41 ʹ 54 ʺ N, 127°43 ʹ 30 ʺ E, altitude 118 m, 19.iv.2019 (3 larvae with 1 ultimate, 2 early instars); ditto, 23.iv.2019 (8 larvae with 3 ultimate, 3 penultimate, 2 early instars) .

Distribution. Korea (Gangwon-do, new record), Japan (Honshu).

Stream information. The two streams, which are the only localities where larvae of T. japonensis were collected so far, were small mountainous stream with rubble and sandy bottom, leading to Bukhangang and Hongchengang River, respectively. There were agricultural fields and houses adjacent to the streams, but the streams were maintained relatively clean. The streams were 3-5 m wide and 5-20 cm deep. The streams were lined with trailing vegetations including reeds. The streams where larvae were collected were partially dried up after May 2019 due to spring drought.

Remarks. Uemoto (1980) erroneously designated the holotype of this species from the female of Bentinck (1955). This species is known as a univoltine and overwinters as an egg and hatches in the late April or early May, so the larvae were mainly collected from middle to late April ( Uemoto, 1980). According to Japanese records ( Bentinck, 1955; Uemoto, 1980), this species was found infrequently from rapidly flowing small streams fed by melting snow at altitudes above 1,200 -1,500 m. Larvae lacked labral fans and used their modified mouthparts to graze food from stones and submerged litter ( Adler et al., 2004), so that the larvae and pupae usually attached themselves to the lower surface of stones ( Bentinck, 1955; Uemoto, 1980), but could be found from various aquatic substances including submerged twigs. Korean specimens were collected from streams with moderate to rapid flow with well-developed submerged reed blades. Many larvae were collected from submerged reed roots at artificial waterways with concrete bottoms. No larvae were collected from stones. Unfortunately, no pupae and adults were collected from Korea. Adults can be seen from early June to early July and possibly bite humans ( Bentinck, 1955; Shogaki et al., 1978; Uemoto, 1980). This species were collected along with commonly collected species such as, Simulium (Nevermannia) uchidai , Simulium (Simulium) suzukii , Simulium (Simulium) yamatoense , Simulium (Simulium) japonicum , and Simulium (Simulium) oitanum .

Distribution. Korea (Gangwon-do, new record), Japan (Honshu).

Figures

Fig. 3. Larva of Twinnia japonensis Rubtsov. (A) Larva, lateral and dorsal view; (B) Head, dorsal view; (C) Head, ventral view; (D) Head, anterodorsal view; (E) Hypostoma, phase contrast photomicrograph; (F) Gill histoblast, phase contrast photomicrograph; (G) Prothoracic proleg, lateral view; (H, I) Posterior circlet, phase contrast photomicrograph; (J) Rectal papillae, posterior view. Scale bars, 2 mm (A); 500 μm (B-D); 200 μm (F, J); 100 μm (G, H); 50μm (E, I).