Culturing Fruit Flies

ARK - Arizona Rivulin Keepers

Culturing Vestigial Winged (Flightless) Fruit Flies

Fruit flies are small insects in genus Drosophila. The most commonly cultured species in our hobby is D. melanogaster. Drosophilia hydei is cultured somewhat less often (being somewhat more difficult to culture). Both are an good source of fish food because 1) they are fairly easy to culture and 2) they remain alive (at least for a short time) on the aquarium water surface waiting to be consumed.

However, cultures can develop a distinctive "yeasty" odor as several weeks so it might be best to keep your cultures in a location agreeable to all members of your household. Mine get tossed out after 4 weeks.

I've described how I culture fruit flies below. It works well for me, but there are probably many others that work as well (if not better). Feel free to experiment!

My Technique

Materials:

a sauce pan
Containers w/lids. Some people use Snapple bottles, others use mason jars. You can use whatever container you want. Personally I use 6 oz. polyethylene bottles with paper lids from Applied Scientific. This is not an endorsement, but just what I do. (They are very good, but not inexpensive though! - $100 for 500 bottles/lids)
Fruit Fly medium (instant potatoes, cornmeal, wheat germ, unsulfured molasses)
Yeast (the kind you bake with)
a 6 oz or larger open mouthed jar
a small funnel
a wide-mouth fly holding jar

Setting it up:
I prepare about 12 cultures at a time (about 3 weeks worth for me). Those not used immediately are stored in the refrigerator.

I begin by mixing all the dry ingredients in a 16 ounce mason jar.

4 cups instant potato flakes
2 cups cornmeal
1/2 cup wheat germ
1 tsp agar (optional)
pinch (1/8 tsp) of mold inhibitor (optional)

Add 800 ml of water to the sauce pan and bring it to a boil. After the water is boiling, I add about 30 to 60 ml of unsulphured molasses. Return to a boil and slowly add the dry ingredients. If you add them too fast, it will clump. When the stuff is the consistence of hot oatmeal, it's done. I add two soup spoons full (2 - 2.5 tablespoons) to each container. This is where the funnel comes in handy, especially if you have narrow necked bottles. You don't need a whole lot here. Just enough to cover the bottom with 1/4" to 3/8" of medium. The larger the container, the more medium it will take (duh!).

Keeping it Going
A culture of D. melanogaster will begin to produce new flies in about two weeks. D. hydei take somewhat longer about 4 weeks). Periodically, you will need to start new cultures. How often, depends on your situation. I start two to three new cultures every 3 days. I remove the bottles from the refrigerator and let them warm up to room temperature. I then add about 5-10 grains of yeast. I grab an existing culture that is about 2 weeks old and full of flies. First, I tap the lid of the fly culture to knock the flies to the bottom of the bottle. I then quickly pop the lid, tip the bottle and tap on the side of the bottle until about 12 flies drop into the new culture (using my handy funnel). Immediately close both cultures. Label it with the date (type of fly if applicable). Doing this quickly and without losses takes practice, but after a few times people generally lose very few in a transfer. And that's all there is to it!

Feeding your fish:
These small insects hop and climb readily. Feeding your fish (and starting new cultures) can be tricky, so here are some tips:

Make sure you have plenty of room for your cultures and other supplies. Before opening the fruit fly culture, gently tap the top of the bottle to knock the flies to the bottom. Act quickly after this as they will immediately climb back to the top! Tip the bottle slightlty (45 degree angle or so) and gently tap the the side to encourage the flies to fall into your tank. Do not turn the culture completely upside-down as you may dump parts of the medium in your tank. When you have fed enough flies, tuen the bottle up-right as you continue to tap (that drops all the flies to the bottom). Pop the lid back on and your set. Until you get the hang of it, there will always be a few escapees when messing with your flies.

What to do with those old cultures?

Bacically, there are two choices: toss them or clean them. You pick.

Here are some other recipes from a friend: Fruit Fly Recipes