A Few Fly Myths Debunked
Adelaide TC Carpenter (atc12 at mole.bio.cam.ac.uk)
Myth 1: Agar for fly food must be boiled for 10 minutes before other
ingredients are added. Bunk! True, the agar-water solution must be
brought *to the boil* in order for all the agar to go into solution, but
just to the boil is sufficient.
The problem is that, at the boil, the agar-water solution foams up
and will make a right mess if it foams over the edge of the pot; fly-food
cooks prefer not to have to clean up such messes so they tend to add the
other ingredients before a full boil is achieved -- not enough agar gets
dissolved so the food is too soft. The ten-minute rule was, long ago, an
attempt to try to get such a cook actually to boil the agar-water
solution. That is ALL.
There are two general solutions to the underlying problem of
getting reliably solid food. The first is to tell your cook to add the
other ingredients *just* as the agar-water solution begins to foam up, but
that it must begin to so foam before the other ingredients are added;
this method is easier to manage if most of the first water is heated to
boiling on its own, with a little left out with which to hydrate the agar.
Adding this hydrated agar to already-boiling water means that the final
solution will reach the boil/foam stage quickly -- no need for an anxious
cook to watch a not-yet boiling mixture for very long.
The second solution is not to boil up the agar alone at all but
rather to add it in dry with all the other dry ingredients, stir it in
well, and hydrate it along with the cornmeal etc (will need a little more
water for this step than usual). Bring the rest of the water to a boil,
add the slurry, and stir continuously (the agar will gel out along the
bottom of the pot if not kept astir) until the whole mixture comes to a
full, rolling, plopping boil. The full mixture will foam up a bit but
nowhere as drastically as simple agar-water: and all the agar does get
dissolved, quite possibly because the full mixture has a boiling point
higher than 100oC.
Do mix all of the dry ingredients together thoroughly before
hydrating; the ones that tend to clump when hydrated alone (notably
cornmeal and yeast) dilute each other out. Add about half the hydrating
water at one go, stir around but don't worry about lumps yet. Let sit a
few minutes and stir again. Presto! All lumps are resolved. Now add
more water, bit by bit, until the slurry is of pourable thinness.
Myth 2: Nipagen M (Tegosept M, methylparaben, 4-hydroxybenzoic acid
methyl ester, methyl p-hydroxybenzoate, Methyl Parasept) is soluble only
in 100% ethanol. Bunk; it's perfectly soluble in 95%, which is
Myth 3: Fly cultures need a light/dark cycle. Bunk! unless you are
doing behavioral studies. Stocks go fine under either constant light or
constant dark -- even the ones that can see. The ones that can't see
anyway go fine even though they can't tell they have a light/dark cycle,
right? And incubators that don't have such controls are less expensive.
Myth 4: Fly incubators/culture rooms need to operate with constantly
alternating heat/cooling cycles. Bunk, at least in most modern building
environments, most of the year. I've been running my 18o walk-in with
just cooling (on a thermostat, of course, so actual cooling occurs
intermittently) for several years now entirely satisfactorily; the air
temperature might fluctuate slightly more than running both heat/cooling
though I suspect not, and certainly the fly cultures themselves act as
flywheels maintaining a constant temperature. 25o should work with just
heating as long as the environment isn't near 25o. Advantages: the
heating/cooling equipment works a lot less, saving both energy and wear
and tear: and so does the humidifier equipment because you are taking
less of the moisture out of the air with the air conditioning. Depending
on your setup you might find the humidity getting too high! (Fly cultures
exhale a lot of moisture.) May not be satisfactory in your own
circumstances but worth a try, even if you have to revert to both cycles
during particularly warm or cool times of the year.
Myth 5: 25o is the ideal temperature for Drosophila melanogaster. Bunk,
of course. What temperature do they prefer in the wild? Room
temperature. 20-22o. 25o is instead the highest temperature at which
most stocks/cultures are still happy, so is useful in terms of quickness
of results, just as 18o is the coolest = longest interval between
transferring stocks. Try keeping your sickest stocks at room temperature
and be amazed at how much better they thrive.