A new cage should be started from 80 synchronous bottles. In a few days the
flies should become acclimated to the cage and start laying a substantial number of
eggs.
Every day the flies in the cage should be fed two to four collecting plates covered
with a thin layer of yeast paste. An empty weigh boat with a couple of moist paper
towels in it will help keep the cage humid, and should also be changed daily.
Setting up fly boxes:
Fly boxes are made from plastic food storage boxes (9" x 6") with a nitex covered
opening (4" x 2") cut in the top. A monolayer of absorbent cotton is placed on the
bottom and the following solution is poured evenly over it:
1 box
water 200 ml
propionic acid 0.13 ml
phosphoric acid 0.75 ml
live yeast 54g
sucrose 27g
Eggs for the fly box are collected in the following manner:
1) Collect eggs on freshly yeasted plates overnight.
2) Under gently running water brush the eggs off the plate into a nitex sieve.
3) Wash the eggs thoroughly with water to remove any excess yeast.
4) Fold a filter paper circle (9 cm) into a cone and place it in a funnel. Using 70%
ethanol, rinse the eggs off the nitex into the filter paper cone.
5) Place a filter paper circle (9 cm) on some paper towels. Transfer some eggs onto the
circle. Then using a small brush and 70% ethanol spread the eggs uniformly over the
circle in a monolayer.
6) Repeat step 5 until all the eggs collected are on the filter paper circles.
7) Allow the filter paper circles to briefly air dry then place on the moist cotton, two
circles per box. Cover the box securely.
8) Incubate the boxes at 25°C. Flies should eclose in about 10 days.
Once the flies eclose they will only live for a day or two in the fly box. The box can be
easily emptied in the following manner:
1) Hold the box upside down and place the CO2 outlet next to, but not through, the
nitex until all the flies stop moving.
2) With the box still upside down, remove the cover and dump the flies onto an open
manila folder.
3) Quickly dump the flies off the folder into an empty fly bottle sitting on ice.
Maintaining the population cage:
To maintain the population cage, three fly boxes are set up to start a new cage. If
possible the boxes should be set up from one overnight collection. If this is not
possible, some effort should be made to synchronize all three boxes so that they all
eclose within 24 hours of each other.
The following is a typical schedule for a fly cage:
1) On Monday start the cage with fresh flies. Between 50-100 ml of flies is desirable
for normal uses.
2) On Friday set up three fly boxes.
3) On the following Friday the cage is cleaned of old flies, washed and dried.
4) On Monday add the new flies from the fly boxes to the cleaned cage and begin the
cycle again.
This method is almost impervious to mite problems since fresh flies are used every two
weeks. It is important to thoroughly clean the cage and fly boxes after each use with
hot soapy water to prevent any contaminates from being passed on.
Collecting eggs for DNA or RNA extracts:
1) Eggs are collected and washed into a nitex sieve as described above.
2) Place the sieve on a flat surface and fill with 50% bleach. Let stand for 2 minutes to
dechorionate the eggs.
3) Rinse the eggs with 2 liters of 0.7% (w/v) NaCl in water.
4) Place the eggs in an eppendorf tube and freeze in liquid nitrogen.
5) Store at -80°C.
Egg collecting plates:
1) Prepare the following mixture:
water 2500 ml
molasses 360 ml
agar 88g
2) Autoclave for one hour.
3) Slowly add:
tegosept
(10% (w/v) methyl p-hydrobenzoate
in 95% ethanol) 0.5 ml
ethyl acetate 20 ml
4) Mix well and pour into plastic weigh boats (5" x 5").
5) Let cool and store at 4°C.
6) This recipe yields approximately 18 plates.