- Chironominae

Non-biting midges

Code QDAG9999

The Chironomidae are the third most speciose family of Diptera with aquatic larvae, after the Tipulidae and Culicidae. The common name for the family is "non-biting midges" after the weak development of the adult mandibles, in contrast to the sister group, the biting midges or Ceratopogonidae which have female mouthparts designed for taking a blood meal. For some larvae, the common name of "bloodworms" is used to signify the presence of the red blood pigment haemoglobin - but not all chironomid larvae are red.

Chironomid larvae are apneustic, with one exception, the amphipneustic genus Archaeochlus that lives on isolated granite outcrops in Western Australia and a few central Australian sites. The prolegs are nearly always present, and paired on the prothorax and final abdominal segment. The head capsule is always prognathous (directed forwards) thus differentiating from Thaumaleidae. For 95% of aquatic species, separation from the Ceratopogonidae, can be made using the prolegs, which are paired and separate. A few Orthocladiinae confuse the situation, and it may be necessary to examine the pharyngeal apparatus which is strong, with divergent arms in ceratopogonid larvae, but weak in Chironomidae.

The ecology of the Chironomidae is very diverse and can scarcely be summarised except for the species-poor subfamilies. Thus larval Aphroteniinae are restricted to sandy substrates with fine organic material overlying. The Podonominae tend to cool stenothermy, are usually lotic, and are usually limited to winter periods. The Tanypodinae are predominantly predators in late instars, though often feeding on diatoms etc. in early instars. The Telmatogetoninae are not keyed because they are exclusively marine intertidal (but so are several genera of Orthocladiinae and a few Chironominae). The Chironominae are all aquatic, and do everything, though there is a preponderance of eurythermic taxa compared to the other subfamilies. The Orthocladiinae tend more to cool stenothermy, but are very diverse and include riparian, terrestrial, phytotelm species.

Larval chironomid species track ecological conditions closely, and their distributions have long been used to assess water quality. This topic is well reviewed by Johnson (1995), in a volume that provides substantial reference to Australian studies of the ecology and systematics of the family (Cranston, 1995). More general information on the family, its systematics, ecology and impacts upon humans are covered in Armitage et al. (1994).

The presently recognised Australian subfamilies can be keyed using some characters visible (with experience and care) under the stereo microscope:

1 Antennae retractile into head. Main feeding mouthpart - the ligula - within the head........................................... Tanypodinae

- Antennae non-retractile. Main feeding mouthpart external, the mentum........................................................................................2

2 Eye paired or triple. Ventromental plates visible alongside mentum................................................................. Chironominae

- Eye single. No ventromental plates.....................................3

3 Small, body covered with tubercles that often trap dirt........................................................................ Aphroteniinae

- Size various, body smooth....................................................4

4 Head capsule with extended, dark neck............ Diamesinae

- No such neck.........................................................................5

5 Procercus many times longer than wide...... Podonominae

- Procercus no more than 2x as long as wide.......................6

6 Marine intertidal.................................... Telmatogetoninae

- Rarely marine.............................................. Orthocladiinae

Characters visible under the compound microscope as follows:

1 Antenna retractile into head. Hypopharynx with distinctive toothed ligula. Mentum usually weakly sclerotised............................................................. Tanypodinae

- Antenna non-retractile. Ligula never developed as in Tanypodinae. Mentum nearly always a dark sclerotised toothed plate ...........................................................................................2

2 Mentum associated with variably developed but always broad, and nearly always striated, ventromental plates. [Exceptionally Stenochironomus and Harrisius lack striations, but some hooks are present]......................................................... Chironominae

- Mentum with, at most, relatively small, non-striate ventromental plates....................................................................3

3 Mentum untoothed. Sensory setae of anterior labrum elongate. Body covered with tubercles and hairs..................................................................... Aphroteniinae

- Mentum nearly always toothed. Labral setae small. Body cuticle smooth but may be strongly setose.............................4

4 Premandibles absent............................................................5

- Premandibles present..........................................................6

5 Second or second/third antennal segments often annulate. Procercus predominantly elongate, many times as long as wide...................................................................... Podonominae

- Antenna non-annulate. Procercus absent............................................................. Buchonomyiinae*

6 Central ligula and lateral paraligulae of prementum resembling 3 brushes. Third antennal segment often annulate.................................................................... Diamesinae

- Prementum never developed as three brushes, although a single median brush (M-appendage) may be present. No annulate antennal segments.....................................................................7

7 Ventromental plates elongate, with beard beneath.............................................................. Prodiamesinae*

- Ventromental plates variable; if large, then never with beard beneath.......................................................................................8

8 Prementum with brush-like M appendage divided into many fine branches, lying ventral to the mentum. Premandible short and broad with strong inner brush. Antenna short, distinctly 4-segmented................................................ Telmatogetoninae**

- No brush-like development of prementum. Premandibular brush absent or weak. If the antenna is 4-segmented and short (less than half mandible length), then the apical segmentation is indistinct........................................................... Orthocladiinae

* Not yet Australian, but may be found here.

** Marine only.

References:

Armitage, P., Cranston, P.S. and Pinder, L.C.V. (eds.) (1994) Chironomidae: Biology and Ecology of Non-biting Midges . Chapman and Hall, London, Glasgow, New York, Tokyo, Melbourne, Madras. p. 572.

Cranston, P.S. (1993) The immature stages of the Australian Chironomidae. MDFRC Workshop key available from John Hawking.

Cranston, P.S. (ed.) (1995) Chironomids: from Genes to Ecosystems , CSIRO, Melbourne. p. 482.

Johnson, R. (1995) The indicator concept in freshwater biomonitoring. pp. 11-27. In: Cranston, P.S. (ed.) Chironomids: from Genes to Ecosystems. CSIRO, Melbourne.