Re: The business of flies
I get a consistent 4-5 weeks of production from my cultures (sometimes as long as 6-7 weeks). A 2-week shelf-life for a culture implies something is wrong:
1) You could be over-feeding from the culture and not leaving enough adults to lay eggs for the next generation. I think this reason is less likely.
2) Your culturing medium could be a bad mix that sours too quickly for your flies to have anymore than 1 or 2 generations. Possible.
3) You might be mixing, or letting your cultures become, too dry. If your medium drops below a critical moisture value, the flies can't reproduce. Also possible.
4) Your flies' genetics might have been adversely selected. It works like this: You create cultures by seeding adult flies from other cultures. If you always seed from young cultures you end up selecting for flies that produce early in the life of a culture but not well after the first or second generation... and if all you have is cultures that produce for 2 weeks and then fail then all you have for seeding is young cultures! In that case you need fresh genetics: You need an older producing culture to use, in addition to a younger culture, for seeding. (Likewise, you don't want to use only cultures that are "old" for seeding because you can select against the genes that help flies in their first or second generation - you want genes for both early and late production.)