Culturing Fruit Flies

About Fruit Flies

There are two flightless varieties of fruit flies suitable for culturing and feeding to finches: the smaller Drosophila melanogaster (in vestigial winged or wingless form), and the larger Drosophila hydei. Note that the mutation which makes Drosophila melanogaster unable to fly is recessive; it is therefore imperative that your culture flies are not permitted to mate with wild (flighted) fruit flies.

Fruit Fly
Fruit fly by André Karwath.
The entire life cycle (egg->larva->pupa->adult) takes about 11 days at room temperature (a few extra days for D. hydei), though it can speed up at warmer temperatures and slow down at cooler temperatures:

Life Cycle (at room temperature)
Egg <1 day
Larva ~6 days
Pupa ~5 days
Adult Lifespan ~6-7 weeks

Fruit fly adults are not very nutritious, but they can be dusted with a calcium supplement External Site prior to being fed to the birds which helps address this problem.

Culture Set Up

You can buy an entire starter kit External Site (contains adult fruit flies, containers, fruit fly medium/food, etc.), or do-it-yourself:

DIY Container Options
Depending on the container chosen, the top can be plugged using:
(Avoid netting- the holes are wide enough to allow wild fruit flies to mate through the netting.)

Temperature, Humidity, & Lighting
  • Temperature of 70-80F (21.1-26.7C) for optimal growth
  • Optimal humidity 70%
  • Ambient room (not direct sun) light during the day & dark at night.

Medium/Food
Fill the bottom of the container to a depth of 2cm with:
  • A commercial fruit fly medium External Site (wet gel-like consistency, follow manufacturer's directions; add few drops of water as needed if drying out)
  • Mashed banana + water (can also add powdered or condensed milk) + ~10 pellets of baker's yeast External Site
  • Mashed banana + coarse digestive bran to stiffen mixture into a paste + baker's yeast External Site
  • 1 cup instant potato powder + ½ cup powdered milk + ¼ cup white sugar + a pinch of baker's yeast External Site

If the home-made medium begins to dry out too soon, add a dollop of mashed banana to the container.

Substrate
Adult flies need material above the medium to climb on to prevent drowning, and larva also need the material to assist with pupation. Therefore, on top of the medium, add one of the following:
  • A ball of Excelsior External Site (wooden craft straw)
  • A ball of plastic straw
  • Plastic canvas
  • Broken skewers
  • Unused coffee filter

Adding Flies
Each container should have at least 10-12 starter flies (you could add 100-150 if you desired). Keep several containers simultaneously to ensure constant supply (multiples of 7 allow for daily feedings).

Maintenance
Every 20-30 days flies should be transferred to new/clean vial with fresh medium. The old container should be washed (discarding the old medium). Keep the area around the culture containers clean; wipe surfaces down using rubbing alcohol. These steps should help prevent problems with mites, mold, and odor. Another method of discouraging mites is to also place culture containers on top of anti-mite paper External Site (sold in rolls). If a small amount of blue or green mold occurs, transferring cultures to clean vials weekly may help control and eradicate it; if black mold is seen, however, the entire culture and flies should be discarded and you will need to start over.

Feeding Fruit Flies to Your Birds

To remove flies for feeding, tap the container firmly to dislodge flies from the top and sides, then remove the top of the container and "tap" the flies* into a plastic cup with a small amount of calcium powder External Site added to it. Swirl the cup of powder with the flies to coat them, then tap the flies from the calcium-powder cup into a smooth-sided serving bowl in the birds' enclosure. *Remember to hold back enough adult flies to continue the culture.

Tips

If culturing indoors, keep a few strips of safe (insecticide-free) sticky fly strips External Site around the room to catch any escaped or unwanted flies that may be attracted to the cultures.

How-to video from Carolina Biological Supply External Site on Youtube


Additional Resources Used for This Article:
Breeding Insects as Feeder Food External Site
Raising Live Foods (Complete Herp Care) External Site
Breeding Invertebrates for Food & Fun External Site
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