Oriental Chironomus: C. alternus Joh.

Chironomus alternus Das, Majumdar and Hazra, 2016

Adult

Male:
Total length 4.6-5.0 mm. Wing length 2.48-2.64 mm, width 0.62-0.68 mm.
Head brownish yellow; thorax yellowish, postnotum dark; wing membrane brown with dark veins; legs brownish yellow.
Head: AR 2.22-2.64. Frontal tubercles 82-89 µm long and 39-47 µm wide. Clypeus with 16-17 setae. Palpal proportions rather unusual, with the terminal segment shorter than the preceding two segments (not noted as being shrivelled) 51-68 ; 34-51 ; 187-204; 170-187 ; 136-153; segment V with alternate bands.
Thoracic setae: acrostichals 14-16; dorsocentrals 12-14; prealars 12-14; scutellars 10-12.
Wing with 1 Scf on brachiolum, squama with 16-18 setae; VR 1.06-1.08 (or 0.92-0.94).
Leg lengths and proportions (micron)

	Fe	Ti	Ta1	Ta2	Ta3	Ta4	Ta5	LR	F/T	BR
PI	900	910	1300	700	580	500	220	1.40-1.45	0.98-1.00	1.78-1.81
PII	1070	860	510	300	180	140	110	0.57-0.61	1.19-1.30
PIII	1180	1060	740	370	290	140	130	0.69-0.70	1.11-1.12

Abdomen yellow, tergites II-V with dark median spots (as in the "flaviplumus-group"). Tergite IX with about 7 medial setae, apparently not in any pale area.

Anal point described as straight but shown with a narrow base. Inferior Volsella with branched setae, reaching beyond end of anal point and to about the middle of the gonostylus, which is hardly narrowed over distal third.

Female not described.

Pupa: Length 5.96-6.08 mm. Yellowish brown in color
Frontal apotome triangular; cephalic tubercles 20-21 µm long an 30-31 µm wide at base.
Thorax rugose, basal ring oval, HR about 1.6. Wing sheath 1.24-1.25 mm long.

Abdomen yellowish brown. Tergite I bare, tergites II-VI with median shagreen, VII-VIII with faint shagreen; segent I with baso-lateral and II with a caudo-laterals PSB; IV with PSA (58-60 x 68-69). Lateral muscle marks obvious. Hook row of segment II with 40-42 hooks, claimed to be separated into two equal halves although not obvious in figure. Caudolateral spur with 4 spines, all pointing to one side. Anal lobe with 128-132 taeniae in multiple rows.
There are other measurements noted, but they are sexually dimorphic characters and the sex of the pupae is not given.

Fourth instar larva:  Length 6.88-9.52 mm. Deep red in color.  No information on larval type and no mention of lateral projections.  Ventral tubules 1.24-1.44 µm in length.
The mentum 180-186 µm wide; appears to be type II (although described as having gradually decreasing teeth) and the central tooth type III.
Ventromentum about the same width as the mentum, but the inner margin appears unusual (actual inner margin not shown?) margin serrated, IPD 112-121 µm. Maxillary palpus well developed with lacinial setae. PE with 14-16 teeth.
Antenna with basal segment 86 µm long, RO about 1/3 from base.  Ratio of antennal segments: 86-90 ; 21.5-25.8 : 8.6 : 4.3 : 4.3 ; AR 2.10-2.22.
Premandible with five teeth and a minute globular structure at its base.
Mandible 156-160 µm long and 49-52 µm wide.  The drawing of the mandible is difficult to relate to the description of a pale dorsal tooth and 4 distinct dark inner teeth (Ty. IIIC?); no mention of presence of furrows or the number of taeniae in the PecM.

Found: Type locality - Namdapha (27.29°N, 96.23°E. 720 m a.s.l.), Arunchal Pradesh.

Noted as showing relationship to the group of species C. circumdatus, C. ramosus, C. striatipennis and C. incertipenis but this is in regards to certain specific characters including the presence of dark median spots on tergites II-V and an anal point narrowed at the base. For these reasons it is tentatively included with the species of the "flaviplumus group". The five branched premandible of the larva does not seem to indicate a relationship to C. javanus.

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