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Water Content

Mark Thorson eee at netcom.com
Sat Jun 14 10:19:03 EST 1997

In article <339C9484.4AA4 at mail.utexas.edu>,
melanie jane pittman  <gloriana at mail.uexas.edu> wrote:
>are you using Carolina's instant or your own formulation? I am not a fly
>person, so I don't know what 4-24 means.

4-24 is Carolina's instant.

>Our RX is:
>2 litres water
>140 ml high fructose corn syrup
>140 gm Yellow corn meal
>12 gm granulated agar
>39 unrefined brewer's yeast
>220 gm 100% liquid malt extract, or 1/10th of a can.
>10 ml propionic acid/10ml EtOH

The problems here are agar and propionic acid.  I want the
formulation to be composed only of materials that can
be bought at any supermarket.  Agar is only sold retail
at Asian food stores, and I don't know any company that
will sell propionic acid to the general public.

>Dissolve the agar over the water, sift the yeast and CM, stirring. bring
>to a low boil. Stir in syrups, simmer for 5-10 minutes. Turn off heat,
>add CCCOOH/EtOH.  Dispense in sterile culture vials and bottles. Cover
>with clean cloth and set for 3 hours. Plug with sterile cotton.
>Is there some sort of problem with the moisture content with the larger
>culture jars when using C's brand?

Moisture content appears to be a very critical factor.
I made my last batch of cultures using even higher
moisture content than before.  They seem less vigorous
then my previous generation.  Before, the larvae were
burrowing throughout the culture medium, but now they
mostly stay within about 5 mm of the top.

Alongside those cultures, I'm running two new experimental
cultures.  One consists of diced Santa Rosa plums, and the
other is diced bananas.  Both were dipped in a solution of
water and active dry yeast.

The last time I used plums, liquid eventually came out of
plums and some adults drowned.  So, this time I've put
a bed of dry dehydrated mash potato flakes under the plums
to absorb any excess water.

I drained the banana chunks well, and didn't put and potato
flakes under them because I think of bananas being a lot
less juicy than plums.  Within the first few hours after
preparing the cultures, a significant amount of water
seemed to have come out of the bananas, and I was beginning
to regret not having tried the old flake trick there, too.

In a day or two, the water appeared to have been resorbed
by the bananas, because there wasn't more than a trace of
liquid left.  At that point I was feeling pretty good about
not having put in the flakes.

But now, about 4 days later, I see standing water again.
I guess they've now entered a new stage of decomposition.
So, I guess the potato flakes would have been a good idea.
Bananas on top of potato flakes will probably be part of
my next series of experiments.

What I'm trying to do is develop a protocol for mass
culture of flies that doesn't require any materials
you can't easily get locally anywhere in the U.S.  That
rules out most mold inhibitors (an OTC treatment for
athlete's foot, Nystatin has been recommended to me,
but I also want to avoid anything that may be toxic).

So far, my culture vessels made out of plastic cups and
paper towels work great.  That part of the plan is
working very nicely.  Maintaining the cultures over a
few generations also has been easy.  The only unsolved
problem left is coming up with a workable replacement
for 4-24.  I think I'm getting close.  If the banana
cultures take off, and if I can solve the water problem,
then I think that's the solution.

One odd thing I've noticed is that my cultures seem to
have attracted local wild _Drosophila_ species.  I'll
have to be careful not to let them get into my purebred
mutant cultures.  These wild ones sure look just like
the _melanogaster_ species.  Are they common throughout
the U.S.?  Is there anything special to look for in them?
I sure wouldn't want to miss an extremely rare $50,000
fruit fly just because I wasn't smart enough to recognize

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