How to Raise Fruit Flies

This is a basic guide to help you raise the most commonly cultured fruit flies, Drosophila melanogaster and Drosophila hydei. Also includes troubleshooting for the most common culturing problems.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Flightless fruit flies
• Fly proof containers with lids
• Vinegar OR methyl paraben
• Water
• Potato flakes
• Brewer's yeast
• Baker's yeast

1. Decide which flies you will be culturing, Drosophila melanogaster or Drosophila hydei. D. melanogaster has a shorter life cycle, but the flies are smaller, approximately 2mm as opposed to 3mm for D. hydei.

2. Obtain your flies. It is recommended that you only use flightless flies for culturing, as wild type flying flies are difficult to contain. You can obtain a starter culture from most pet stores that cater to reptiles and fish, but they can be purchased on the internet through various sources, or obtained from biology labs at schools or research facilities. There are many different strains of D. melanogaster especially, and you will have the most choice if you purchase them online. If choosing one in person, make sure to pick a culture with lots of flies and no mold.

3. Next you will need containers to culture your flies in. There are many different types of containers that can be used. Glass or plastic jars and disposable deli cups are the most common. Special perforated insect container lids can be purchased for deli cups, but if you are using containers with solid lids, you must cut a hole in them in order to keep from suffocating your flies. Cover the hole by sandwiching a layer of screen or a paper towel between the lid and the container.

4. The next step is to prepare your medium. A simple recipe for medium is 1 part brewer's yeast to 10 parts potato flakes. In a separate container, mix either 1 gallon of hot water with four grams of methyl paraben or a half and half mixture of vinegar and water. Pour the dry medium in the bottom of your containers and add a pinch of baker's yeast. Then add liquid and stir until it is the consistency of pudding. Use at least 1" of medium for D. melanogaster or 2" for D. hydei.

5. The next step is to add your flies. Tap the container with the flies against something to make them fall down. Then open the lid and tap about 50 flies into the container with new medium and swiftly cap it with the lid before they can climb out.

6. The last step is to place them in a spot where they will get temperatures as close to 77F as possible and wait. The approximate life cycle of D. melanogaster is 8.5 days at this temperature, longer if higher or lower. At the same temperature, D. hydei is 30 days. It does not matter if there is light or not, so they can be kept in a cabinet or other dark place out of sight.

Tips & Warnings

• If a culture looks too soupy, then you can sprinkle the dry mixture on top to firm them up.
• If they look too dry and start to show cracks in the media, then add water.
• To keep the flies from drowning in case you need to add water, you can add folded coffee filters or excelsior to the medium before adding flies. Take about 10 coffee filters and fold them into a pyramid shape, then stick it point down into the medium. Excelsior can be purchased at many craft and hobby shops.
• Flies should not be exposed to temperatures over 90F (32C) as it makes them sterile.
• Discard any cultures that develop mold. Do not open them or use them to create new cultures.
• Keep an eye out for grain mites, which are nearly microscopic arachnids that live on the medium. If you see moving specks on the sides of your culture, you have mites. They can spread to other cultures since they are small enough to fit through even the tiniest gaps and can ride the flies into the new culture if you use a contaminated culture. You can get rid of them by using Tedion solution, and prevent their spread by using insecticidal shelf paper, or spraying products meant for bird mites on paper towels and sitting your containers on them.