North American Chironomus

Species 3s. C. tardus Butler 1982.

Adult:

Male: Dark species, AR 5.39 (5.09-5.78); frontal tubercles 20-40 µm.
Weak or absent scutal tubercle.
Abdominal segments dark, but often pale on posterior margins.
Fore leg with moderate beard, BR 4-7. LR1 1.01-1.14 ; LR2 0.56-0.64; LR3 0.67-0.73. Sensilla chaetica: Leg2 21-46; Leg3 15-34
Segment TIX with 8-31 setae. Anal point relatively narrow; superior appendage of the D-type of Strenzke (1959); inferior volsella parallel over entire length
(unlike C. prior where they turn outward over the distal third) and slightly longer than the anal point and about to the midpoint of the gonostyle, which is relatively narrow and narrows only slightly over the posterior third.

Identification: The lower LR1 and the higher number of sensilla chaetica are useful for separating this species from C. prior.

Female: Thoracic color slightly lighter than that of the males, base color light to medium brown,
with scutal stripes, postnotum, etc., dark brown. Abdomen similar color to males.

Pupa not studied in detail, but noted that the hooks on abdominal segment II have a relatively straight point at quite a sharp angle, and the convex margin often has several small teeth. In this regard they differ from those of C. prior which are sickle shaped, generally with a smooth outer margin.

Fourth instar larva a salinarius type. Very dark gular region, dark frontoclypeus, but rest of head paler. Ventral head length 351 (320-386) µm; head width 662 (629-717) µm. Head capsule larger and paler than that of C. prior.

Cytology: 4 polytene chromosomes with the thummi arm combination: AB, CD, EF, G.
Centromeres heterochromatinized. Nucleolus terminal on arm G and proximal on arm D. No polymorphism known.
tarA1: 1 - 2c, 10 - 12, 3 - 2d, 9 - 4, 13 - 19 i.e. as holomelas, cucini, magnus, etc.
tarB1: Differs from magB1 by small inversion about 1/3 from distal end.
tarC1: May be similar to neocoraxC1; inverted c.f. islandicus and cucini just distal to middle of arm.
tarD1: 1 - 3, 11 - 18d, 7 - 4, 10 - 8, 18e - 24 ie. as in longistylus, cucini, etc., other than for the nucleolus.
tarE1: 1 - 3e, 5 - 10b, 4 - 3f, 10 - 13 i.e. as cingulatus, staegeri,cucini, etc.
tarF1: 1 - 10, 17 - 11, 18 - 23 i.e. as in cucini, magnus, tenuistylus, etc.
tarG1: terminal nucleolus.

Found: Alaska - Pond S, Barrow; Loon Pond, Prudhoe Bay (Type locality).

Tundra ponds.

Description of larva by Butler (1982) and cytology given by Wülker & Butler (1983).
This species is the sister species to C. prior.

[ See also C. prior | Return to Index| Go to References ]