Thanks for your question about flies. You chose an interesting experiment. Many people are studying how flies are attracted to different scents, because flies are a model system for studying the sense of smell. If we can learn how flies sense smell, it will help us to learn how humans sense smell. Your choice to study perfumes and colognes is a good one. Although they are not natural substances in a fly's environment, they contain something that is: alcohol. Flies like to feed on rotting fruit (that's why some flies are called "fruit flies"). When fruit rots, wild strains of yeast feed on the fruit and result in fermentation, which results in the production of alcohol. The flies are attracted to the smell of the yeast and the alcohol produced by the fermentation. In fact, in the laboratory, flies prefer food with yeast in it.
In your experiments, you may want to use a piece of fruit (like a ripe banana) or a paste made from adding a few drops of water to some bread yeast (the kind in the packets at the supermarket) as a positive control. The flies should respond to these attractants, and you can compare their response to these natural odorants with their response to perfumes. There have been many experiments done to determine things that attract flies. The book Biology of Drosophila edited by Milislav Demerec ( Cold Spring Harbor Press, 1994; Library of Congress Catalog number 94-68751) has a chapter starting on page 538 describing things that attract flies. The types of fruit to try are: banana, pineapple, tomato, and peach. You can even add some yeast to the fruit to start the fermentation process. Try comparing fermented fruit to fresh fruit out of the refrigerator. Also, try comparing bananas at various stages of ripeness to see which ones the flies prefer. If you need to collect flies for your experiment, that book chapter explains how to make a trap. If you need more information, let us know.
--David Miller
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