Chironomus occidentalis Skuse, 1889

Synonyms: Incorrectly synonymised with Chironomus australis by Freeman 1961.

In BOLD Bin: BOLD:AAJ0166

Adult:


Original description of Chironomus occidentalis from Skuse 1889

This specimen was examined when in the collection of the Macleay Museum and some additional details recorded.  Since the Skuse description, the antennae and the remains of the hind legs have been lost:
Wing length (measured from brachiolum, consistent with my other wing measurements) 6.26 mm.  Palps (segments 2-5 in micron): 70 : 270 : 250 : 430: P5/P4 1.72, P5/P3 1.59.
Thoracic setae could not be counted accurately but there were at least 14 dorsocentrals and at least 5 prealars.Leg lengths (micron) and proportions:

 
Fe
Ti
Ta1
Ta2
Ta3
Ta4
Ta5
LR
F/T
Ta4/Ti
PI
2020
1800
-
-
-
-
-
-
1.12
-
PII
2020
2040
1120
660
500
340
280
0.54
0.99
 

Note: type specimen is a female.  The descriptions below include the first description of the adult male, as Freeman (1961) synonymised the species with Chironomus australis McQuart.


Lake Sepping, Albany, W.A., type locality of C.occidentalis

Male:
A large species with the anterior tarsi of the male strongly bearded; Leg ratio about 1.2-1.3.
Wing length 5.64 (4.72-6.10) mm., width 1.26 (1.04-1.36) mm; VR about 1.02–1.07.  AR about 3.78 (3.33-4.29).
Frontal tubercles present, length about 49.3 (28-70) micron and about 3 times longer than wide; 38.5 (25-70) clypeal setae.  Palpal lengths (micron): 89 : 82 : 285 : 298 : 456; P5/P4 - 1.51 (1.27-1.63): P5/P3 1.6.
Thoracic setae: acrostichal - about 13.6 (10-25); Dorsocentrals - 20.2 (13-27); prealar - 6.5 (5-9); supra-alar - 1; scutellar - anterior 11.5 (5-13) often in 2 rows, posterior 14-19.
Scutellum with 27.4 (15-34) setae in at least two rows; anterior with 11.5 (8-16) setae (higher numbers generally in two rough rows), posterior with 16.4 (14-19) setae.
Leg lengths (microns) and proportions as follows:
 
Fe
Ti
Ta1
Ta2
Ta3
Ta4
Ta5
LR
F/T
BR
PI
1797
1737
2214
1171
871
776
380
1.26-1.34
0.99-1.07
4.21-7.08
PII
1983
1902
1125
667
450
351
266
0.57-0.64
1.01-1.08
 
PIII
2402
2223
1668
996
753
481
295
0.65-0.70
0.96-1.02
 

Abdomen with a brown stripe and darker anterior/posterior medial extension on tergites I-V, then segments VI-IX completely darkened.  5.2 (4-8) setae in a single paler patch on tergite IX.


Male terminalia of C.occidentalis

Superior volsella closest to E(h) type of Strenzke (1959); Inferior volsella reaching at least half way along the gonostylus, with simple setae.  Gonostylus moderately swollen and reducing gently over about the posterior third to half; with 7+1 setae at distal tip.  Anal point narrow and darkened.

Female:
Wing length about 6.20 (5.61-6.75) mm, width 1.73 (1.63-1.88) mm; VR 0.92 (0.88-1.00); 5 (3-7) Scf on brachiolum; 20.9 (13-29) setae on squamal fringe  Crossvein slightly darkened.
Head: Frontal tubercles variable, 49.8 (15-81) µm long and 2.43 (0.75-2.7) times longer than wide.  Antenna 5 segmented, proportions (micron) and fraction of neck in brackets: 237 (0.25) ; 142 (0.48) : 179 (0.47) : 143 (0.45) : 293; AR - 0.42 (0.37-0.46); A5/A1 - 1.21 (1.12-1.34).
Palp lengths (micron): 90 : 75 : 258 : 286 457; P5/P4 - 1.45-1.74; P5/P3 1.77 (1.50-2.00).
Clypeus 1.86 (1.4-2.5) times the diameter of the antennal pedicel, and with 49 (40-67) setae.
Thoracic setae: abt. 20 acrostichal; 2-6 approx. linear humerals beginning about 1/3 from pronotum; dorsocentrals abt 21-29; dorsocentrals (incl. humerals) 27.7 (19-44); prealars 8.2 (6-10); supraalar 1.3 (1-2); scutella setae 20.7 (14-25) larger setae in posterior row, 21.5 (12-28) generally smaller setae in 2-3 anterior rows, total 40.3 (26-51).
Leg lengths (micron) and proportions:
 
Fe
Ti
Ta1
Ta2
Ta3
Ta4
Ta5
LR
F/T
Ta4/Ti
PI
1909
1822
2273
1064
793
729
372
1.21-1.31
1.01-1.12
0.41
PII
2082
2048
1112
623
437
310
248
0.50-0.57
0.95-1.07
 
PIII
2474
2624
1681
950
739
445
284
0.62-0.67
0.90-1.00
 

Abdomen with darker band, sometimes extended a little posteriorly in the midline, over the anterior 2/3 of segments I-VI, then over most of tergite.  GcIx with 3-7 setae; SegX curved and 3.9 (3.34-4.30) times longer than wide, with 15.9 (12-20).  Cercus with a generally curved outlinewith a large ventral and a small dorsal basal bulge.

Morphologically very similar to C. australis and C. duplex, but is distributed allopatrically to them on the west of the continent.
The adult is about the same size as C. australis and slightly larger than C. duplex

C. occidentalis can be readily separated from C. duplex at the pupal stage on the basis of the pupal spurs, in which the spines (about 5-6) are closely applied in C. occidentalis but spread in C. duplex.  The pupal spur of C. occidentalis resembles that of C. australis.

Found: Northern Territory: Magela Creek, Mudginberri Station (12.75°S, 132.88°E).
            Western Australia: King George Sound (Holotype location)(35.03°S, 117.93°E); Cape Naturaliste (32.53°S, 115.03°E);
            Crawley (31.99°S, 115.82°E); 3 Km w. Esperance (33.85°S. 121.87°E); Lake Monger (31.93°S, 115.826°E),
            Township of Cambridge; Lake Sepping, Albany (33.85°S, 152.87°E); Upper Swan (31.77°S, 116.03°E).

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Modified: 13 July 2023
Access: Unrestricted
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