6b. Chironomus nr. 'castaneum' n. sp.

This species is recognized as close to C. 'castaneum' on the basis of the cytology and mtCOI sequences.

Probably in Bold Bin: BOLD AAL7010.

Two males, one a somewhat incomplete reared male were available for my study.  The name C. campomelus is suggested for this species and the adult male from Lake Hawea, Otago, South Island NZ.48.1 male 1 (7.I.1974) has been chosen as type since there is also DNA barcode data for this specimen.

Adult:

Male:  AR about 3.7 - 3.9.  Wing length 5.37 mm, width 1.09 mm (type).  LR about 1.33 - 1.52, anterior tarsi without a beard (BR about 1.7).
Frontal tubercles present, length about 40-69 Ám long and 16 - 18 µm wide.Palpal proportions (micron): 78 : 56 : 280, 278 : 420.  About 26 clypeal setae.
Thoracic setae - acrostichals - at least 10; dorsocentrals - about 22; supra-alars 1; scutellar in two rows 10 anterior, 17 posterior.
Leg proportions (micron):
 
Fe
Ti
Ta1
Ta2
Ta3
PI
1392-1700
1316-1680
2000-2240
1139-1320
810-1000
 
PII
1544-1820
1468-1810
873-1030
557-630
380-440
 
PIII
1797-2120
1835-2260
1342-1540
835-940
557-680
 
 
Ta4
Ta5
LR
F/T
BR
 
PI
633-820
304-340
1.33-1.52
1.01-1.06
1.7
 
PII
266-290
203-230
0.57-0.59
1.01-1.05
 
 
PIII
354-420
228-250
0.68-0.73
0.94-0.98
 
 

Fore Ta5/Ti about 0.15 - 0.23.  Sensilla chaetica difficult to see, perhaps 4 mTa1, 7 hTa1.

Abdomen with somewhat triangular brown markings on the tergites, narrowing towards the posterior margin, and become progressively wider on successive segments.
About 9 setae at centre of 9th tergite; Superior volsella closest to the E(h) type of Strenzke (1959); setae on Inferior volsella simple.  Gonocoxite IX narrows markedly from about the distal third to half.

Female: (from a specimen collected by I. Hogg, in BOLD database):
Wing length about 4.3 mm.  Colour brown with darker brown postnotum and dark bands across basal part of abdominal segments at least II-VI.  Legs apparently relatively pale with no darkening at knees: Mid femur abt. 1.48 mm; mid tibia about 1.24 mm (F/T abt 1.19); hind femur abt. 1.92 mm, hind tibia at least 1.9 mm (F/T about 1).

Pupa:  Length about 9.4 mm.  Pedes spurii B developed on segment II, and about 55 hooks on posterior margin.  Pedes spurii A well developed on segment IV.
Caudolateral spur of segment VIII with about 3 to 6 spines.
Anal lobe with about 132 tainiae on each side.

Larval Morphology:  A salinarius-type larva, length 12.7 - 17.2 mm (female); 12.3-14.8 mm (male).  A larva from Winton showed a small bump for the posterior VT (about 0.06mm).  Anal tubules short (200 - 400 µm) and rounded, only about 2-3x (1.8 - 3.2) longer than wide.
Frontoclypeus and posterior half to two thirds of gula, dark to very dark, sometimes with some slight darkening at posterior of head capsule.
Mentum of type II, c1 tooth of mentum broad, 6th laterals turned out.
Ventromentum with about 35-40 striae, which reach almost to the anterior margin, particularly at the lateral edges.
Pecten epipharyngis with about 10-14 teeth narrowing towards the edges.  Distance between antennal bases less than the distance between the S4 setae.
Antennae with basal segment about 2.38-3.38 times longer than wide, AR 1.92-2.55; Ring organ about one third (0.30-0.35) up from base of segment; proportions (µm) 146 : 35 ; 9 : 13 : 8 ; A3 shorter than A4, but longer than A5.
Mandible type generally type IIB, but sometimes 3rd inner tooth darker and more distinct IIC, and with about 20 - 25 furrows on outer surface near base.

Cytology: 4 polytene chromosomes, with the pseudothummi group arm combination (BF, CD, EA, G).
Distinguished by two nucleoli in chromosome 1 (1 proximal in F and one proximal in B).    Arm A with a sequence differing from A4 of C. oppositus by a simple inversion which is also found in C. forsythi; arm E commonly differs from E1 of Australian species by a large inversion, although E1 appears to be present in Poutu Canal population.    Arm F1 appears identical to that of oppositus F3 and australisF1.    Arm G often partly unpaired.    Polymorphic in arms A, B, C, D, E and F.

camA1:    1a-e, 2e - 3, 1f - 2c, 10 - 11, 2d, 8 - 9, 3f-i, 12c-a, 4 - 7, 13 - 19        as zeaA1 & casA1
camA2:    1a-e, 2e - 3, 1f - 2c, 10 - 11, 2d, 8 - 9, 3f-i, 12c-a, 4 - 7, 13 - 19                i.e. as casA2 (Haast)
camB1:    Nucleolus just distal to 4 characteristic bands (groups 24 - 26), and puff with distal dark bands (groups 8-7) near distal end.         i.e. as casB1
camB2:    Inversion of distal third of arm, as nzlB3, bringing puff and proximal dark bands (groups 7-8) close to nucleolus.            i.e. as casB2
camB3:    Inversion of region of the nucleolus, from camB2  (different breakpoints to the difference of camB1 to forB2).
camC1:    Characteristic band groups 3-4, with 5 distal, near distal end.                            i.e. as casC1.
camC2:    simple inversion of distal third from camC1.  (in NZ.67.1 Em#1)
camD1:    as casD1
camD2:    as casD2
camE1:    1 - 3e, 10b - 3f, 10c - 13                            i.e. as oppE1, etc., casE1>
camE2:    1a-e, 3f - 10b, 3e - 2a, 10c - 13                            i.e. as casE2
camF1:    1 - 2a, 10 - 2c, 15c - 11a, 2b, 15d - 23                        i.e. as casF1.
camF2:    inversion of distal third of arm
camG1:    with small subterminal nucleolus
camG2:    from camG1 by a smaller inversion around the median BR than that differentiating camG1 from forG1.  (NZ.67.1 Em#1)

Click here to see chromosome BF heterozygous for the inversion in each arm.

Known Localities
North Island:
      Lake Karapiro, South Auckland (NZ.77.1) (Sofia Ibarrarán) 27-viii-2007
      Lake Okaro, South Auckland (NZ.10.9) (Sofia Ibarrarán) 14-ii-2007
      Lake Rotoaira South Auckland (NZ.77.1) (Sofia Ibarrarán) 14-ii-2007

South Island
      Haast junction, 3 km w Haast, Westland (NZ.67.1) (Jon Martin) 25-i-1978
      c.1 m in Lake Te Anau, Te Anau, Southland (NZ.46.2) (Jon Martin) 7-i-1974
      Lake Hawea, Otago (NZ.48.1) (Jon & C.J. Martin) 7-i-1974
      Owaka River, South Otago (NZ.56.1) (T.Dodgshun & J.S.Pillai) 14-iii-1974
      Creek at Winton, Westland (NZ-43-1) (Jon Martin) 5-i-1974

This species differs from C. 'castaneum' in that the markings on the abdominal tergites are not bell-shaped, and the anal tubules of the larva are more tubular.
The cytology and the MtCOI sequence suggests that there is hybridization between C. nr. castaneum and C. analis, since at least one specimen has been found with the C. nr. castaneum cytology, but the C. analis CO1 sequence.
There is currently no close match to the COI sequence in the NCBI or BOLD databases.

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Modified: 22 March 2019
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