Asian Chironomus: C. javanus

C. javanus Kieffer 1924

Synonyms: All suggested synonyms are doubtful as most probably refer to C. vitellinus.

Chironomus daitocedeus Sasa & Suzuki, 2001 (Yamamoto, unpubl.)(probably C. vitellinus)
Chironomus prasinellus - Tokunaga 1940 (misidentified) but Sasa & Kikuchi, 1995.
Chironomus vitellinus Freeman 1961 (Chaudhuri et al. 1992) – incorrect synonymy (see Chironomus vitellinus).

Yamamoto (2002) has suggested that this species should be in a separate subgenus Austrochironomus, as type of the subgenus. However there is doubt that there is a consistent set of characters for the species he included.

In BOLD Bin: BOLD:AAG6924.
There is no meaningful nearest neighbor to this bin.
Most specimens in the Bin are actually C. vitellinus, with only a few C. javanus.

C. javanus and C. vitellinus are closely related and there is clear evidence that some hybridization can occur in the limited area where both species occur together, e.g. in Malaysia.

Adult:

Kieffer's original description of C. javanus.
Female. Yellow. Eyes separated by not more than their terminal width, gradually thinning at the top. Palps long, brownish black, 4th segment matching the previous two segments combined, 2nd shorter than 3rd, 1st much longer than wide [these are actually segments 2-5]. Antenna 2nd segment narrowed in the middle, the neck a little longer than wide, the rest broken. Metanotum, three short bands, mesonotum and mesonotum reddish. Halteres light green. Wing whitish, not distinctly stippled, veins a whitish yellow, crossvein and base of the cubital black, cubital arched, ending very near the tip of the wing. Legs light green, fore tarsus long and thin, white, both ends of segments 1-4 deep black, 5th slightly clouded, pulvilli a little wider, with long hairs, not exceeding the middle of the crotchets, hardly shorter than the empodium, probably branched four hind tarsi broken; fore femur much longer than the tibia, the latter and the tarsal segments are 2 : 3 2/3 ; 2 : 1 1/2 : 2 : 3/4 [i.e. LR = 1.80], the 4th segment is longer than 3rd, the four hind tibias have confluent combs which occupy two thirds of the circumference, the two spurs short. Abdomen a bright green, unmarked. L. 4 mm.
Male. Pale yellow, abdomen spotless, four bands on mesonotum, metanotum and mesosternum fawn, red scape, flagellum broken. Wing as female. Legs white, distal end of tarsomeres 1-4 and 5th tarsal segment black. Anterior tarsus broken. Eyes separated by 1.5 times their terminal width. Terminal articles of the genitalia ('pince') arcuate, the distal half suddenly narrowed in a straight beak, glabrous, having only one third of the width of the proximal half and carrying on the distal half of the medial side straight six large rigid bristles. Superior appendages very thin, glabrous, linear, reaching the end of the basal article (gonocoxite), weakly curved and ending in a point; inferior appendages large, pubescent, exceeding just the gonocoxite and bearing dorsally the usual long and thick curved setae. Anal point long and thin. L. 4.5 mm.

Many specimens attributed to C. javanus are actually C. vitellinus and C. javanus appears to have a relatively restricted distribution in India, Java, and Malaysia.

Male:
A yellowish-green species with dark bands on the tarsi and darkening of the cross veins of the wings.

Other than the original description, the only reliable further descriptions for this species are those of Johannsen (1932) and Chaudhuri et al. (1992)(whose specimens appear to be larger, possibly due to being reared in laboratory), plus a specimen from Penang:

Thorax yolky colour, dull with practically no pruinosity, Chaudhuri et al. (1992) describe the coloration as more brown than yellowish. Anal point narrow, pencil like, not expanded at the distal end.
Wing length 1.96 (1.92-2.03) mm, width 0.62 (0.56-0.63) mm; VR 1.06 (1.05-1.08); perhaps 8-15 setae in squamal fringe.
Head: Frontal tubercles present, abt 32x18 µm (1.8 times longer than wide); about 16 (14-16) clypeal setae; AR 3.05(sic.) (3.69-3.82).
Palpal proportions (segs. 1-5): 2 : 2 : 7 : 8 : 11; P5/P4 1.38; P5/P3 1.57 (Penang specimen 40 : 27 : 140 : 170 : 133(shrivelled) µm).
Thoracic setae: abt 10 acrostichals ; 13 (12-14) dorsocentrals; 2 prealars; 0 supraalars; abt 7-8 scutellars near anterior margin and often not evident.
Wing: Hyaline, length 1.96 (1.92-2.03), width 0.62 (0.56-0.63); VR 1.06 (1.05-1.08); brachiolum with 2 SCf; squama with 20 (15-26) setae.
Leg proportions and ratios (microns)(Chaudhuri et al. 1992):

Male	Fe	Ti	Ta1	Ta2	Ta3	Ta4	Ta5	LR	F/T	BR
PI	1150	1000	1120	955	840	770	350	1.60	1.12-1.15	no beard
PII	1205	1135	695	360	270	175	130	0.64-0.74	1.16-1.18	-
PIII	1330	1335	1050	570	440	280	155	0.77-0.82	0.99-1.00	-

Tergite IX illustrated without setae, but the Penang male has two rows of long setae across the tergite - 7 in an anterior row and 6 in a more posterior row (below). If these setae were lost in preparation it is possible the tergite would appear to have lacked setae.

TIX showinng the rows of setae
Note the abdomen is squashed towards the bottom right, and the two brown masses at left are the displaced IVo's.

Hypopygium with long tubular anal point, strongly turned down. Superior volsella well developed and curved, perhaps closest to E(h) of Strenzke (1959); Inferior volsella reaching just beyond the end of the Superior volsella, about 1/3 of gonostylus length, with 12-14 incurved setae. Gonostylus quite swollen and conspicuously narrowed over posterior half with 5+1 or 1+4+1 setae at tip.

Illustration of the hypopygium of C. javanus
From Johannsen (1932)

Female
The female has hardly been described as Kieffer gave few metrics, so the only information appears to be from Chaudhuri et al. (1992):
Body length 3.69 (3.57-3.89) mm.  Wing length not given.
Antennal segments (micron): 10 : 7 : 8 : 9 : 13; AR 0.38; A5/A1 1.3.  Necks of segs. 2-4 about 50%.
No information on palps, clypeus, thoracic setae or legs.  Kieffer gives abdomen as green, unmarked.  Cercus almost pointed at posterior end, large bulge on ventral margin.

Pupa and Fourth instar larva: See C. javanus immatures.

Cytology: The chromosomes of C. javanus have not been studied, but there is a photograph which is probably this species (below): Four polytene chromosomes with the thummi-cytocomplex combination AB, CD, EF, G. Centromeres are obvious but not heterochromatic. Essentially terminal nucleolus in arm G, possibly with a BR close to it. A large puff is developed about one third from the distal end of arm B. No reported polymorphism.

Molecular: The mitochondrial CO1 barcode sequence is available in GenBank and the BOLD database for a few specimens. Although the sequences in BOLD are in a single Bin, there is a suggestion that the distribution is bimodal, with the few C. javanus sequences separated to the right of the main group. The BARCODE sequences differ by about 47 base positions (this does not include some rare polymorphisms where one or two C. vitellinus specimens carry the sequence present in C. javanus), and the majority are in the 5' region (as is common for differences between closely related Chironomus species):

There is one specimen from Penang (MYA.1.3 BMAES 11F) in which the COI sequence is that of C. javanus, but the larva is typical of C. vitellinus – suggesting that the female parent was C. javanus and the male parent C. vitellinus. This is in the small region in which both species are known to co-exist.

The present measurements differ in some significant details from those of Kieffer's description, although the other details of colour and the unusual genitalia correspond.

The males are easily recognised by the unusual genitalia, particularly the tubular anal point, and the larvae by the 6-toothed premandible. The pupa is a fairly typical for Chironomus.Males can be separated from the relatively similar C. vitellinus by the tubular anal point rather than expanded at the distal end (see below ) and the placement of the setae on TIX, although that species has been regularly misidentified as C. javanus as can be readily seen from the figures of the male hypopygium. The larvae can be separated by the number of teeth on the premandible (6 vs. 7 – so the excellent photograph of the premandible in Cranston (2007) is C. vitellinus, not C. javanus), the unusually short 3rd segment of the antenna (shared with C. vitellinus) and the teeth of the mandible (type II-IIIA vs type IIIC).

Found:Type locality - Buitenzorg, Java, INDONESIA, also Sumatra (Johannsen 1932).
India - Bankura, Chinsura, Dhaniakhali, all West Bengal (Chaudhuri et al. 1992); Madurai (9.925°N, 78.120°E), Tamil Nadu; University
of Jammu Campus (32.73°N 74.87°E) Jammu & Kashmir; Kasar Lake (18.82°N, 76.20°E), Kulcatta.
Indonesia - Sumatra.
Malaysia - Minden, Penang; Tregganu; Bukit Merah Agricultural Experimental Station (BMAES) Permatang Pauh, Penang
(5.13°N, 100.13°E); Parit, Perak.

Apparently limited distribution through India, Java and Malaysia, in rice paddies and small temporary water bodies, even sewage works.

The redescription of adults and immatures from Malaysia by Al-Shami et al. (2012) clearly refers to C. vitellinus but they did also collect at least one specimen of C. javanus (figure above).
Dr. Midya has an alternative species from India identified as C. javanus and L. Karunakaran described another species as C. javanus in an unpublished thesis (Martin 2022).

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