After suffering poor yields due to the cold weather,
I discovered something that should have been obvious.
Keeping my cultures warm for the first four days after
starting results in good yield even if they spend the
rest of their time at low ambient temperature (about
50 to 60F). They take longer to mature before harvest,
the time being highly temperature dependent, but yields
(I don't know if less than four days would also work,
but I have enough warm shelves for four batches of
It appears that the critical period when they need to
be warm is so the yeast can proliferate and outcompete
all of the other microbial species in the culture medium.
Duh! Wish I'd tried that sooner!
I had been puzzled why I get so many wild flies entering
my house even after weeks of frost in the morning. How
can wild Drosophila reproduce in such cold weather while
my cultures were hit so hard? The answer appears to be
that Drosophila can tolerate cold if they have access to
food. It's yeast that can't tolerate cold. I don't know
where wild Drosophila live in the winter or what they eat,
but they must be finding something.