My Experiment

Mark Thorson eee at
Mon Feb 24 22:21:02 EST 1997

I've just started my mass culture for _D._melanogaster_,
and I'd be interested in any constructive criticism of my

First, I should state my objectives.  I want a system for
growing a fairly large quantity of flies.  I don't know
exactly how large a quantity will be sufficient, but I'd
estimate to the nearest order of magnitude 100 grams dry
weight per month.

This system must be something that could be constructed
from materials available to the average citizen.  That's
because I have a SECRET PLAN to popularize growing fruit
flies as a hobby.  Oy, do I have a plan!

A bit of a snag I've run into is that Carolina Biological
Supply won't sell mold inhibitors like methyl paraben or
fly anaesthetics like Fly-Nap to the general public, only
schools and industry.  So, I'm concentrating on designs
that avoid the need for either.

Because this hobby would be promoted among non-biologists,
it would be a plus if the system hides the larvae and mold
from the fly-breeder.  Less icky that way.  What I want is
a disposable, no-clean system, so that when the culture is
spent, you just bag it up and throw it away.

My first experiment has about one and a half kilograms
of sliced bananas for the culture medium.  I thought it
would be best just to slice them, not mash them, so that
I wouldn't be distributing mold or bacteria spores throughout
the culture medium.  Only the surface would be contaminated.

Also, I dipped the banana slices in a solution of water
and a packet of active dry yeast (yeast sold for making
bread).  I guess yeast is an important component of fly
food, though I don't know if it's just for the vitamins
or whether it competes with mold too.

My culture vessel is a tall plastic wastebasket with a
tapered rectangular cross-section.  This particular
design had a separate pop-up piece in the lid, so by
removing this piece I had a hoop that fit closely on the
top of the waste basket.

I lined the wastebasket with two garbage bags of an
appropriate size.  I put one bag inside the other, as
a precaution against leaks or tears.  I covered the top
with a piece of cloth sold as a "flour sack dishrag".
I was going to use cheesecloth, but the mesh appeared
too coarse to me for this purpose.  The hoop makes a
fly-proof seam around the top of the wastebasket, holding
the bags and cloth in place.

For harvesting purposes, I've made an opening in the cloth.
I took a styrofoam coffee cup and cut off the top and
bottom to make a small cone, open at each end.  This fits
into a larger cone, which is a coffee cup with just the
bottom cut off.  I use pins to hold the cones together with
the cloth in-between.

Right now, I've just got a third coffee cup on top of
the harvesting port, to act as a cap.  When I start
harvesting, I plan to use another open cone made from
a coffee cup to act as a retaining ring to hold a plastic
baggie in place.  I plan to rely on the climbing behavior
of the flies and the attraction to light to lure them into
the baggie.

The fly-breeder only needs to see adult flies.  The larvae
and mold stays at the bottom of the wastebasket, and when the
culture is spent, he or she just gathers up the top and
tosses it out with the garbage.  My plan is perfect!  Now
I just need to demonstrate that it works.

One mistake I think I made already is that I didn't seed
the culture right away with the flies from Carolina.  I
waited until the original cultures had visible larvae
in them, and by then the number of adults had declined
considerably.  If I had seeded the mass culture with more
adults, I think I would be further ahead of the race with

Another possible mistake is the use of bananas.  Is there
another fruit these flies can eat?  My whole apartment
smells of bananas.  What about plums or apricots?  I'm
going to get tired of bananas real quick.

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