Culturing Fruit Flies
Flightless fruit flies are an easy-to-culture feeder insect for small reptiles and amphibians. They can be purchased from reptile or biological supply companies, as well as some specialty pet stores. There are two species commonly available - Drosophila melanogaster and Drosophila hydei. The main differences between the two species are the adult size of the fly and the time that the flies take to go through their life cycle. D. hydei is the larger of the two, with adult flies measuring around 1/8 inch (3 mm) D. melanogaster matures to a smaller size of around 1/16 inch (1.5 mm). D. melanogaster takes roughly two weeks (depending on temperature that cultures are kept at and medium used) to go from egg to maggot to adult fly, and the newly morphed flies can reproduce after 24 hours. D. hydei develops slower and takes roughly one month to go through its life cycle. D. melanogaster is commonly available in two separate mutations: flightless and wingless. The flightless variety has wings but they are vestigial and can not fly.
The Container: The container that fruit flies are cultured in has to be escape proof but also ventilated. Many people use mason jars, screwing down paper towel over the top to provide ventilation. Another option is plastic 24 oz. or 32 oz. deli containers. Holes can be cut in the lid and fitted with a foam plug. There are also plastic containers designed specifically for housing invertebrates that come with ventilated lids. These can be purchased from places like Black Jungle Terrarium Supply or in bulk from Superior Enterprise. Containers can be put in the dish washer or rinsed with hot water and re-used.
Culture Medium: The medium is what serves as food for both the larvae and the adult flies. It can be purchased from both biological supply companies and some specialty reptile supply stores, or you can choose to make your own. By making your own medium you can save substantial amounts of money if culturing large amounts of flies. Below are two recipes for homemade media I have used with success. Consider modifying and experimenting with them to suite your needs.
The "Harvey Peterson Medium"
1 part white sugar
2 parts powdered/instant milk
4 parts instant mashed potatoes
Combine dry ingredients together, and then mix with equal parts water in a culturing container. For D. melanogaster 1/2 cup of medium with 1/2 cup of water seems to work well in 32 oz. containers. Use more medium for D. hydei.
The "Power Mix Medium"
In three separate containers...
1 mushed banana
½ can of grape juice concentrate
14 oz. of applesauce (half of a large jar)
1/8 cup of molasses
1 cup of instant mashed potatoes
½ cup of brewers yeast
1 cup of water
1 cup of vinegar
Once the boiled mix has cooled to a reasonable temperature add 6 tablespoons of it to a standard 24 oz. or 32 oz. plastic container. Then add 6 tablespoons of the dry mix and then 2-4 tablespoons of the water/vinegar mix and stir very well. The amount of water/vinegar mix that is added will depend on the humidity where the cultures are kept and how ventilated the containers are. Let it all sit for a few minutes until it solidifies. I find that this medium produces extremely high yields of very large, healthy flies. Unfortunately, it is not easy to make and takes more time to setup cultures that the Harvey Peterson medium mentioned above.
Baker's yeast should be added to cultures once the media sets. Between 5-20 granules of yeast per culture is usually enough. Some people find they have best success mixing yeast with warm water and sugar and then pouring a spoonful or two into each culture. Once yeast and medium are added, flies can be placed into cultures. Use between 25 and 75 flies per culture.
- Store the cultures in an area where the temperature does not fall below 70°F (21°C) or rise above 85°F (29°C). The flies will go through their life stages faster when kept at higher temperatures and slower when kept at lower temperatures.
- You can increase the amount of flies produced by adding extra egg-laying sites to the culture. Fruit flies will lay their eggs on pretty much anything solid. You can sink pieces of cardboard, poster board, or aluminum window screening into the medium to form extra solid egg-laying areas. Excelsior, commonly sold as American moss at craft stores, works very well for creating additional egg-laying sites.
- Do not mix different strains of fruit flies in one culture. You may end up with flying fruit flies if you do.
- Setup cultures weekly even if you do not need the flies. It's better to have too many flies than not enough.
- Only use flies from healthy cultures to setup new cultures, avoiding using flies from cultures over 3 weeks old or that may be molding.
- If mold is noticed in a culture, throw the culture out. Mold is a common problem, and spreads easily if not contained.
- Discard cultures after 5-8 weeks even if they are still producing to avoid mite and mold problems.
- Write the date that you setup a culture on the cup to keep track of when you should start new cultures and dispose of old ones.
- Re-use your culturing containers, which can be put in the dishwasher or soaked in the sink with hot water to clean them