A careful maintenance regime is essential in order to achieve useful fly yields
Looking after Drosophila is quite easy when you get the hang of it. When cultures crash it's usually because they were left unattended for too long. The life span (just like the development time) is temperature dependent, and does not much exceed 2 weeks as a fly. It is critical to follow a careful regime to allow maximum production. This can take a few minutes each week and that's it. HOWEVER, miss a week and your yield will be drop, miss 2 and you may well loose your cultures! If flies are left too long over old media, they will also starve, and provide a poor snack for the fish. If you can not attend to the flies, its best to keep them cool, slowing down their life cycle (20 deg C) until you can tend to them again.
In general flies should be kept at around 25-28 degrees C. This provides a quick turnover of flies for feeding and allows a weekly regime to be followed. They also like a relatively high humidity; If yours are not kept in a humid room, consider keeping the vials in half a centimeter of water.
So how does the regime work?
The vials that the flies inhabit are separated into 3 categories:
Once per week newly emerged flies are collected from 2. These are placed in fresh vials, and are designated 1, the present generation. After 3-4 days these flies are moved again, onto new media 3. The old vials (which are loaded with eggs or very young larvae) go back in 2, to make future generations. Once the week has passed, the flies making the present generation can be fed to your fish, and their vials may either go back into 2, or be left for a few days to provide larvae for feeding (see part 5 - feeding fish). Of course a new generation of adult flies is again collected from 2 at the same time.
In hot weather, and if things are going well, you will soon have a lot of flies. On the other hand, you may struggle to breed enough to satisfy your fish. But always avoid feeding newly emerged flies to your fish, even if you have no shortage of flies 'coming through'. Newly collected flies may well be hungry. It's always a good idea to place them over fresh media with added brewers yeast for 24 hours before feeding them to fish, ensuring they are plump and healthy before feeding to your killies.
There are many advantages of keeping to a strict regime such as this: