We normally inoculate about 60 tubs with 0.17 to 0.2 grams of eggs. The flies that eclose approximately 2 weeks later are distributed evenly among 3 cages. Three cages of adults will usually generate at least 200 grams of eggs over the course of 6 days. A small portion of these eggs are used to start a new population of flies whereas the majority of eggs are used to make extracts for biochemical studies.

Before you start, you need approximately 60 tubs of food that are at room temperature. You will probably need two grape plates of eggs, although sometimes one plate will be enough if the flies are laying heavily.

Collecting eggs and inoculating tubs:

1. Remove a grape plate from a cage. Put a fresh grape plate carrying a 1 inch wide, 1/8 deep strip of yeast paste in middle back into the cage of adult flies. It is very important to add a new plate to the cage of adults if others intend to collect eggs. Without food, the adults starve and die in about 24 hours.
2. Set up the collection apparatus with two screens. A coarse screen placed at the upper level filters out adult flies whereas a fine screen placed at the lower level catches the eggs. Have available a squirt bottle with water and a second squirt bottle with 70% ethanol. A clean tub and paint brush are also needed.
3. Transfer the eggs from half a plate into a clean tub. You will work with half a plate at a time so that the eggs are not left for long before they are transferred to tubs. Sprinkle a little water on the eggs on one half of the plate. Using the paint brush, sweep the eggs into a plastic container. Rinse with additional water to transfer the majority of the eggs into the container. Set aside the grape plate with the remaining half of the eggs for later use.
4. Suspend the eggs by stirring with the brush, and then pour the eggs into the collection apparatus. Rinse eggs from the brush and container on to the top screen of the collection apparatus.  Rinse the eggs through the top screen with additional water. Remove the top screen where adults are trapped and set this aside. Rinse the eggs with about 100 ml water to remove yeast. Then rinse the eggs with about 100 ml of 70% ethanol.
5. Carefully remove the screen and set it on a stack of paper towels; the eggs will be on top of the screen. Allow the ethanol to absorb into the paper towels. Transfer the screen to a fresh stack of paper towels if the eggs are still very wet.
6. After a few minutes, the eggs should be dry enough to transfer to the tubs. Place a 1 to 2 inch square piece of parafilm on the balance. Transferring with a spatula, weigh out 0.17 to 0.2 grams of eggs. This will be a clump of material about the size of a pea. Transfer this to the center of a cornmeal tub. Repeat inoculating tubs until you run out of eggs.
7. Squirt a little water on the clump of eggs in each tub so that the clumps disperse.  Sprinkle 1/2 tablespoon of dry, active yeast around the perimeter of each tub. This yeast goes by the name of "Saf" yeast - it is dry and granular. Avoid adding an excessive amount of yeast, and avoid covering the eggs with the yeast.
8. Cover the tubs with screened lids and place the tubs on the metal shelves in the fly room.
9. Repeat the procedure with another half a grape plate until all of the tubs are inoculated. If the grape plates do not appear dried out, scrape off the old strip of yeast, rinse with water, wrap in plastic and put back into the cold for reuse. If the plates are dry and cracked, discard them.

Transfer of adults to cages (for more information on setting up the cages, go here):
The adults will begin to eclose approximately 12 days after the eggs were placed in the tubs. Sometimes, the majority of adults will eclose in unison. When this is the case, one session of transferring adults into cages is often sufficient to set up the cages for egg collections. Unfortunately, the adults often do not eclose in unison. In this case, you should transfer adults on several days: perhaps 12, 14, and 16 days after the tubs were first inoculated. The reason for multiple transfers is that the adults become unhealthy if left in the tubs for more than a few days. You can gauge when to stop transferring adults by carefully examining the pupae on the sides of the tubs. When 70% or more of the pupae look empty, the tub can be terminated.