Here is how to minimize the disruption to your fly work (and therefore your experiments) when you plan to be away from the lab for many days.

Crosses for Building New Stocks#

  • For any crossing scheme, you should have the entire plan written out before you start, so you should know when you start that you won’t have a stable stock by the time you’ll be away. Assuming you’re diligent about collecting flies and have enough copies of the cross at each step, two weeks per generation is a good estimate for the timeline.
  • Once you’re about one to two generations out from the time you’ll be away, it should be clear when you’ll have the parents for the cross that will overlap with the time you’ll be away. That is, if you were to continue on your current trajectory, will they eclose while you’re away? Or will you have them collected 3 days before you leave?
  • The ideal situation is to have the cross set up before you leave and to have enough vials to collect from when you get back. There are a couple ways to do this:
    • Make sure you have enough parents in hand to set up the desired number of copies of the cross about a week before you have to leave. Set up the crosses at 25 deg, and flip the crosses after 2-3 days, as usual. After at least 2 days at 25 deg for any given vial, move the vial to 18 deg. (Setting up a cross at 18 deg will work, but crosses do much better when the parents are given a few days at 25 deg to mate and lay eggs.) Flies take 2X as long to develop at 18 deg compared with 25 deg. Importantly, this applies even if you move the flies from 25 deg to 18 deg; the remaining development time is approximately doubled. For example, a cross started at 25 deg for 3 days and then moved to 18 deg will take about 15-17 days total to eclose; a cross started at 25 deg for 1 week and then moved to 18 deg will take about 12-13 days total to eclose. In other words, by setting up the cross early and then moving various flips to 18 deg after an appropriate amount of time, you can make sure the flies don’t eclose until you get back while ensuring you have enough vials to collect from. With this approach, it is better to delay the crossing scheme by one generation to ensure that you have enough parents several days before you leave than to push through one more generation.
    • Set up the crosses and ask a labmate to flip them for you every few days while you’re away. Depending on how long you’ll be gone, asking them to move earlier flips to 18 deg can ensure you won’t miss any virgins.
    • If you’ll be gone longer than about 2 weeks, the first approach doesn’t work very well, as the flies will eclose before you get back, and the second approach may be less than ideal as the earlier flips will eclose before you get back and the later flips may not produce as many progeny as you need. You can instead collect the parents in separate vials and keep them at 18 deg, and then ask a labmate to put them together and flip them every few days on a timeline that means you’ll be back before the flies eclose.
    • Of course, the last option is to ask a labmate to continue the crossing scheme as if they were you, collecting virgins and genotyping and such as needed. However, as elaborated on below, this would be a very big favor you’re asking for.
  • If you need virgins from a stock for future crosses, remember to expand those while you’re away as well. The first 2 approaches above work just as well for stocks in vials or bottles.

Experimental Crosses#

  • You can get clever with temperature for your crosses for building stocks, but I don’t recommend doing that with your experimental crosses, as that will introduce a variable you really don’t want to have to worry about.
  • Instead, ask a labmate to flip your experimental crosses for you.
  • Set up new copies of the crosses right before you leave, so they won’t die out before you get back.
  • If you’ll be away for long enough that you’re concerned the cross will die out before you get back even if you set it up right before you leave, collect the parents, keep them at 18 deg, and ask a labmate to set up the cross some time into your time away such that they eclose right when you get back.

Stock collection#

  • Be aware of when your stock collection is due to be flipped, so that you know in advance that it’s due when you’ll be away
  • If that’s the case, you should probably flip your collection early, before you leave. If it’s due only a few days before you get back and your usual flipping schedule incorporates that amount of leeway, then flipping late is okay.
  • Flipping so early that the first progeny haven’t yet eclosed (less than 12-14 days from the date of last flip for stocks on white food at room temp) is not a great idea, as you’ll be relying on old flies to propagate the stock instead of new ones. Being in this situation (i.e. flipping when you get back is too late) means you’re probably away for >3 weeks, so hopefully, you know about that well in advance. I recommend shifting the previous flip early as well as the current one so that each flip has enough time.
  • If you shift the flipping schedule for one copy of your stock collection, you should shift the flipping schedule of the other copy correspondingly so that they stay optimally staggered.

Asking Your Labmates to Do Your Fly Work#

Asking your labmates to help you out with your fly work when you’re away can prevent you from waiting for experimental flies or from failing a multi-generational crossing scheme. You should definitely ask them for help. That being said, some types of fly work are small favors and some types of fly work are big favors, and you should be cognizant of what you’re asking.

Small Favors#

  • Flipping some vials or bottles
  • Moving vials between incubators
  • Combining pre-collected and pre-genotyped flies together to set up a cross (ideally, just by flipping some vials)

Big Favors#

  • Collecting virgins
  • Sorting flies by genotype (e.g. collecting progeny from a cross)
  • Flipping your stock collection

Since your labmates are doing you a favor, it is polite to make their work as easy as possible. This also minimizes the chances of a mistake (you’d think this would be pretty hard, but it’s actually not because everyone organizes and labels their fly crosses slightly differently). Specifically:

  • Make all the labels necessary for all the new vials/bottles you’re asking them to generate.
  • Organize the boxes in such a way that it’s obvious which vials/bottles they need to work with and which ones they can ignore. Bonus points if you have boxes containing only the ones they need to care about.
  • Detailed written instructions
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