Please follow these guidelines for maintaining your stocks:

• Maintain all your stocks in duplicates. A stock can be easily lost due to mold or just random infertility events. You must keep 2 copies of all your stocks (i.e., 2 separate vials or bottles). The flipping schedule for the 2 copies should be staggered, ideally by one-half the time between flips. This provides robustness to random events (e.g. a poor batch of food) and allows you to always have a vial to scrape a couple virgins from if you get desperate.
• You should keep your stock collection at room temperature or at 18 deg C. You’ll have to flip less often if you keep them at 18 deg C, but unhealthy stocks may not reliably make it at that temperature.
• We generally maintain our stocks in white food vials, though very sick stocks may do better on molasses.
• With our current food, stocks on white food at room temperature should be flipped every 4-5 weeks. On molasses at room temperature, the ideal time between flips is probably 3-4 weeks. The time between flips is ideally the max amount of time that still allows you to reliably propagate all your stocks. Reliably as in losing both copies of a stock is something that happens a handful of times during your tenure in the lab, and losing a transgene (i.e. all the stocks with that transgene die) is vanishingly rare.
• Stocks that you are using for current experiments and/or crosses should generally be kept in bottles or vials separate from your stock collection. Bottles if you need a lot of flies and vials if you don’t. Your stock collection just maintains that genotype of flies from generation to generation, and the less you handle them, the lower the chance that they become contaminated or that you accidentally kill them by taking too many virgins.
• It’s a good idea to look at your stocks under the microscope every few months to make sure that the appropriate genetic markers still exist.