We commonly rear midges from field collected egg masses or from egg masses
laid in the laboratory.nbsp; nbsp; There have been a number of rearing techniques
published, but we have
found the following to be the most useful:
We commonly rear midges from field collected egg masses or from egg masses
laid in the laboratory.nbsp; nbsp; There have been a number of rearing techniques
published, but we have
found the following to be the most useful:
Rearing medium
0.04% (w/v) NaCl - this was recommended for Chironomus
tentans by Case & Daneholt (1978). While good for large species,
smaller species may require additional nutrients.
Walter's solution - developed for European species which
normally
live in Na+- CO3- - waters, by Walter
(1973):
To 100L water is added: 0.5g NaHCO3, 3.5g NaCl, 2.7g
CaCl2, 0.2g KH2PO4, 3.0g MgSO4,
1mL 1% FeCl3.
Martin's solution - developed for Australian species that
live in Na+- Cl- - waters, by Martin (Martin et al. 1980):
To 4L of
water add
1mL/L of the following salt concentrates (each in 100mL water) - 1.0g
NaHCO3; 5.0g NaCl; 1.0g CaCl2; 0.2g
KH2PO4; 1.0g MgSO4; 1.8g
MgCl2.
To this is added 0.2mL/L of a 0.1% FeCl3 solution; 0.25mL/L of
solutions of
0.6g/100mL Thiamine HCl and a mixture of 5g
NH4C2H3O2, 0.1g
MnCl2, and 0.1g KI in 100mL water.
We use perspex containers (bottom row in figure), into which we put 4L of medium.
Three to five shredded Kleenwipe, or 8 to 10 shredded single-ply toilet
tissues (avoid recycled paper products, as these appear to be detrimental to the larvae) are
added for the larvae to use as additional food and from which to build
their tubes. If wear on the larval mentum is not of concern, the addition
of a thin layer of stone dust (ie. the dust produced when stones are cut
with a power saw - usually available from building suppliers or plant
nurseries) will produce larger, healthier larvae with better quality
polytene chromosomes.
Additional tissues may be added each week as needed.
Moderate aeration is required to provide sufficient oxygen for the larvae. An aquarium stone will build up algal and other deposits and may be a source of contamination between containers, so I use about 14 or 16 gauge hypodermic needles, which can be easily cleaned. Some people believe aeration should not be supplied in the first few days after setting up an egg mass, but we have found no problem with providing aeration right from the start in order to prevent the formation of a film of scum on the water surface.
Temperate zone species are reared at 20oC, tropical species at
25oC, with a light regime including a morning and evening
‘twilight’ period: 1 hr low light; 14hrs full light; 1hr low light; 8hrs dark. The actual wattage required will depend upon the size of the room being lit. Unfortunately the introduction of ‘low wattage’ globes is making it difficult to get the 25W or lower incandescent globes that are best for the ‘twilight’ periods.
Feeding
A variety of foods have been recommended for rearing chironomids, including
powdered nettle leaves (Case & Daneholt 1978), TetraMin fish food, powdered
milk, Trout Starter 1c (ie. the finest food given to fingerling trout) which is ground with a mortar and pestle, and even chocolate coated dog kisses (Biever 1965).
We use a mixture of a "Total Essential Nutrition" floating pellet and a Chiclid pellet, ground and fed at
the rate of 0.2g (for a single egg mass) or 0.4g (for a mass rearing cage) per week, but almost any sinking pellet fish food is suitable after grinding.
I have found that feeding preferences of larvae may vary between continents, for example Australian Chironomus species do not seem to do well on the crushed nettle leaves so favoured for European species.
This technique has been used for rearing, but not necessarily breeding,
species of Chironomus, Kiefferulus, Dicrotendipes, Conochironomus,
Microtendipes, Polypedilum, Riethia, Tanytarsus, Paratanytarsus,
Cricotopus and Procladius.
Some species will breed in the rearing cage, but for others the adults need
to be collected and put into a separate breeding cage about 1m below the
room lights. We have found that any Australian species that is going to
breed in the laboratory will breed in a 30cm cube cage, comprising a wooden
frame covered with mesh (Top row in figure). A white enamel dish of water is placed on the bottom
of the cage, into which the females will deposit their eggs.
In some cases only about 8 - 10 males are necessary, but for others at least
20 - 30 males are needed before successful mating will occur. The ease of mating under laboratory conditions can vary markedly between closely related species. Species with the enlarged hypopygium that commonly accompanies mating on the substrate, are usually the easiest to breed under laboratory conditions.
References
Biever, K.D. (1965) A rearing technique for the colonization of chironomid
midges. Ann. ent. Soc. Am. 58: 135-136.
Case, S.T. and Daneholt, B. (1978) The size of the transcription unit in
Balbiani
Ring 2 of Chironomus tentans as derived from analysis of the primary
transcript and 75 S RNA. J. Mol. Biol. 124:
223-241.
Martin, J., Kuvangkadilok, C., Peart, D.H., and Lee, B.T.O. (1980)
Multiple sex
determining regions in a group of related Chironomus species
(Diptera: Chironomidae).
Walter, L. (1973) Sytheseprozesse an den Riesenchromosomen von
Glyptotendipes.
Chromosoma 41: 327-360.