Simulium (Gomphostilbia) songense Takaoka, Srisuka & Fukuda, 2020

Takaoka, Hiroyuki, Srisuka, Wichai, Fukuda, Masako & Saeung, Atiporn, 2020, Twenty-one new species of the Simulium (Gomphostilbia) asakoae species group (Diptera, Simuliidae) in Thailand, with their genetic relationships, ZooKeys 950, pp. 51-152 : 51

Simulium (Gomphostilbia) songense Takaoka, Srisuka & Fukuda sp. nov. Fig. 21

Material examined.

Holotype: Female (thorax for DNA analysis) (with its associated pupal exuviae and cocoon) (in 80% ethanol) labeled as "Holotype: Simulium songense male, QSBG col. no. 60, Thailand, 25-VII-2017, by W. Srisuka", collected from a small stream (width 80 cm, depth 2.5, fast flow, pH 7.2, 20.1 °C, partially shaded, elevation 1,157 m, 19°11'10.3"N, 101°04'41.7"E), at Nam Dan Village, Pua District, Nan Province, northern Thailand, 25-VII-2017, by W. Srisuka (Coll. No. 60).

Paratype: One female (thorax for DNA analysis) (with its associated pupal exuviae and cocoons) (in 80% ethanol), collected from a small stream (width 40 cm, depth 3.5 cm, bed sandy, moderate flow, pH 7.36, 21.9 °C, partially shaded, elevation 582 m, 18°45'30.2"N, 100°20'11.4"E), at Chao Wa Waterfall, Song District, Phrae Province, Thailand, 16-III-2017, by W. Srisuka (Coll. No.164).

Diagnosis.

Female: mandible without distinct teeth on the outer margin (Fig. 21A ). Pupa: short stalk of the ventral pair of gill filaments being half the length of the interspiracular trunk (Fig. 21B ).

Description.

Female (N = 2). Body length 1.9 mm.

Head. Frontal ratio 1.9:1.0:2.6; frons:head ratio 1.0:4.9. Labrum 0.65 times length of clypeus. Maxillary palpus: proportional lengths of third, fourth, and fifth palpal segments 1.0:1.1:2.6; sensory vesicle 0.26-0.29 times length of third palpal segment. Lacinia with nine or ten inner and 13 outer teeth. Mandible (Fig. 21A ) with 19 or 20 inner teeth and lacking distinct teeth, though outer margin undulated, appearing to have three weakly developed teeth at some distance from tip.

Legs. Foreleg: basitarsus moderately dilated, 5.5 times as long as its greatest width. Midleg: tarsus dark brown to brownish black though basal half of basitarsus dark yellow or light brown (its border not well defined). Hind leg: coxa light brown); tibia yellowish white on basal two-thirds and light brown to brownish black on rest; tarsus brownish black except basal seven-tenths (though base light brown) and basal half of second tarsomere yellowish white; basitarsus 6.2 times as long as wide, and 0.7 and 0.5 times as wide as greatest widths of tibia and femur, respectively; calcipala nearly as long as width at base, and 0.6 times as wide as greatest width of basitarsus; claw with large basal tooth 0.46 times length of claw.

Wing. Length 2.0 mm.

Abdomen. Dorsal surface of abdomen medium to dark brown except most of segment 2 ochreous (though narrowly darkened along posterior margin).

Terminalia. Sternite 8 bare medially, with 28- 31 medium-long to long hairs together with three or four slender short hairs on each side. Ovipositor valves each moderately covered with microsetae interspersed with three to four short hairs. Paraproct in ventral view with four or five sensilla on anteromedial surface; paraproct in lateral view 0.5 times as long as wide, with 29-32 medium-long to long hairs on ventral and lateral surfaces. Cercus in lateral view 0.5 times as long as wide.

Pupa (N = 2). Body length 3.0 mm.

Head. Integument yellow.

Thorax. Integument yellow, moderately covered with round tubercles except dorsolateral surface of posterior half sparsely covered with tubercles. Gill (Fig. 21B ) composed of eight slender thread-like filaments, arranged as [3+(1+2)]+2 from dorsal to ventral; common basal stalk 0.7-0.8 times length of interspiracular trunk; stalk of ventral pair of filaments 0.6-0.8 times length of common basal stalk, and 0.5 times length of interspiracular trunk; primary stalk of dorsal triplet lying against that of lower pair at angle of 70° when viewed laterally; filaments of dorsal triplet subequal in length (1.8-2.0 mm) and thickness to one another; filaments of middle triplet subequal in length (2.1-2.2 mm) and thickness to one another; two filaments of ventral pair subequal in length (2.4-2.5 mm) and thickness to each other and 1.4-1.7 times as thick as six other filaments of dorsal and middle triplets when compared basally; all filaments yellow to light brown, gradually tapered toward apex; cuticle of all filaments with well-defined annular ridges and furrows though becoming less marked apically, densely covered with minute tubercles.

Abdomen. Dorsally, all segments light yellowish; segments 1 and 2 without tubercles; segment 9 with pair of wide flat terminal hooks (Fig. 21C ), of which outer margin 2.5-2.6 times length of inner margin and crenulated when viewed caudally.

Cocoon (Fig. 21D ). Pale whitish yellow, slipper-shaped, moderately woven, widely extended ventrolaterally; anterior margin thickly woven medially, without bulge or short projection; individual threads visible only on peripheral portions; 3.4 mm long by 2.4 mm wide.

Male and mature larva. Unknown.

Etymology.

The species name, songense , refers to the district, Song, one of the two localities where this species was collected.

Distribution.

Thailand (Nan and Phrae).

Discussion.

Lacking teeth on the outer margin of the mandible, the female of this new species seems to be most similar to S. myanmarense and S. monglaense from Myanmar ( Takaoka et al. 2017b), but is distinguished from the latter two species by the relative length of the fore basitarsus against its greatest width (5.5 in this new species versus 6.0 in S. myanmarense and 6.7 in S. monglaense ).

Figures

Figure 21. Female and pupa of S. songense sp. nov. A female B-D pupa. A mandible (right side) B gill filaments (left side; lateral view) C terminal hooks (caudal view) D cocoon (dorsal view). Scale bars: 1.0 mm (D); 0.1 mm (B); 0.01 mm (A, C).