Scientists have used fruit flies, or the scientific genus Drosophila, as an animal model for experimentation and the study of genetics for a long time for many reasons. You too can catch, learn to raise and study Drosophila. Fruit flies offer an exceptional opportunity to learn about insect lifecycles, how to maintain cultures of insects, genetics and animal behaviors. [NOTE: I know that this is not a fruit fly, but Popillia japonica Newman]
Expected Time Requirement
This experiment could last several days to several months or more depending on the involvement.
Materials
- Overripe/rotting fruit
- Jars or small tubes with tight fitting lids
- #150 or #200 mesh screen
- home-made or commercial media
- glass Petri dish
- freezer
- magnifying glass or low power microscope
- fruit flies
How to Identify Drosophila
Fruit flies are the small (1/10th to 1/16th inch; 1 to 2 mm) flies that we often see around overripe fruit, banana peels, or sometimes yeast rich breads. They typically have red eyes and distinctive black bands around the abdomen. They often have wings but can be wingless. An online resource which might help if you have a question if the flies you see are indeed Drosophila would be FlyBase
Obtaining Drosophila
Probably the best way to get fruit flies is to catch your own. A very simple method of trapping fruit flies would be to use a jar with a paper funnel with the end pointing in the jar you can use some rotting fruit or a few drops of cider vinegar to attract the flies. Other more elaborate traps are possible as well.
If you have liquid in the bottom you might want some fine screen that stands off the bottom of the jar to prevent the flies from drowning. While sticky traps are good at catching flies of all kinds, the flies are stuck to the trap and cannot be recovered for study (except as damaged dead specimens). Check your traps regularly and make sure you only keep them out as long as you need to catch a sufficient number of flies to start your culture. This helps prevent the breeding of unwanted insects like mosquitoes and prevents contamination of your flies with bacteria and fungi.
Alternatively you could purchase cultures from a variety of sources. Many amphibians and reptiles eat fruit flies as food so you can try a local pet shop that sells amphibian related supplies. Or you can order online from suppliers like this one.
You might also talk to a research fly supplier like the Tucson Drosophila Stock Center.
Keeping Drosophila
Like any other animal drosophila need appropriate food and shelter. Your first thought should be what you will keep your flies in. Small jars and milk bottles are just fine if you clean them properly and make sure that they are sterilized before you use them. You can make a 10% household bleach solution which will sterilize well cleaned bottles. Don’t bake your bottles in your oven to sterilize them, most are not made of glass that can take being heated in the oven and will likely break not while you are heating them but when you go to take them out of the oven!
Another way to go is to buy vials that are designed for keeping and breeding fruit flies from a vendor .
The advantage is that they already have a tight fitting lid with a porous plug that allows air (oxygen) to enter the vial. If you decide to use your own bottles, remember that you will need to make some holes to allow air in BUT that won’t let small files escape. You could use hot glue to carefully seal some screening to the top making sure that there are no gaps. A mesh size of #150 or #200 is probably a good size, remember these flies are SMALL.
Some people suggest that you place something into the container on which the flies can pupate, others say that the flies will pupate just fine on the walls of the container. Anything that you put into the container should be clean and sterilized before you do so. Things like paper probably should be avoided as they can start to rot easily.
You also need to feed your flies. Fruit flies actually eat yeast that is growing on overripe or decaying plant material, that is why you see them often on spoiling fruit. Fruit has a lot of sugars, and the sugars make it easy for yeast to thrive. There are a variety of commercial mixes and preparations that you can buy from places like here , here , or here .
You can also make your own media, there are many recipes that are used by researchers around the world you can find some here or here. The liquid in the media is the only supply of water for your flies and is where they lay their eggs, it may take some trial and error to get the amount of water right so that you don’t wind up with a mess.
Anesthetizing Flies
From time to time you may need to take some of your flies out of the container that they are in perhaps to move them to a new container or to separate them out if you plan to try crossbreeding them. A great suggestion found here tells us that we can simply cool the flies in the freezer for a few minutes and then we can transfer them without having to worry that they might fly away. You can even transfer them onto a cooled surface, like a glass Petri dish with a piece of coffee filter on the bottom that has been placed onto an ice or cold pack if you want to study them for short periods of time.
Ideas for Experiments
An excellent activity would be to record the life cycle of the fruit fly. Fruit flies undergo complete metamorphosis (egg, larva, pupa, adult). You can record the length of time spent in each of these stages. Use a magnifier and observe the flies, draw pictures of each life cycle stage.
Observe the mating behaviors of the fruit flies. Can you learn to distinguish between male and female flies? What are their courtship behaviors? How long does courtship last? Do fruit flies provide care for their young?
Using a cooled Petri dish and a magnifier or microscope, study cooled fruit flies carefully. As you raise fruit flies look for flies with unusual physical characteristics. When you find one, separate this fly from the others and try to raise offspring from this fly. Place a single female fly into a fresh tube with a single male fly. With what frequency do you find this mutation to occur in the offspring from these flies?
How long do flies live? Separate out individual adult flies into fresh tubes as soon as possible after you observe them emerge from their pupa state. Do you see any difference between the males and females for lifetimes? If you put a male and female into the same tube is there a difference in their lifespan? How about several males or females?
Other resources
Because fruit flies are so widely used in research, there are great resources available on the internet to help you obtain, keep and study Drosophila.
The Bloomington Drosophila Stock Center
The WWW Virtual Library: Drosophila
The University of Arizona Center for Insect Science Education Outreach (Fruit Fly Rearing)
Flygrower’s Supply Company – Culturing Fruit Fly FAQ
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