Do Fruit Flies Like Germinated Grain Better Than Fruit?

We had fruit lying around our kitchen, and, eventually, we brought fruit flies in with them. One day, when we set out some grain to germinate, we noticed something very intriguing. Instead of hanging around our fruits, the fruit flies began hanging out in mass numbers around our germinating grain. We set up an experiment to test whether it was just a fluke, or whether something was actually going on.

After you’ve watched the video, check out the article below for a more in-depth description of the experiment.

After first noticing the fruit flies preferring the germinating grain in our kitchen vs fruit, we felt that if we can prove that drosophila look for the same things that we ourselves need in our food, that they can be considered as “living” detectors for good food. Andrei did his research, and his hunch was right; fruit flies will look not just for fruit, but for any food with the right carbohydrates, protein, and fats, as well as signs of microbiological activity, like that of bacteria or yeasts.

In order for this experiment to be legitimate, we needed to gather two things:

1. A lot of fruit flies

2. A place where there was no other food besides what was being tested

3. A way for fruit flies to land on whatever they liked best without influence from other nearby food or previous drosophila activity

To breed the drosophila, we looked up standard laboratory methods and procedures for breeding them. Using food grade agar agar, yeast, and sugar, we made a suitable environment for the drosophila larvae to hatch and grow. We attracted them inside the jars with lemons, fruits, and germinated grains, and after there was a sufficient population in our 3 jars, we carefully sealed whatever drosophila that was sitting inside by stretching a piece of cloth over the opening and holding it there with a rubber band.

Then, we waited. 2 weeks later, we had a lot of fruit flies. Our estimation is that there were at between 100-200 flies per jar.

We transferred them to our library which was on the other side of the house from the kitchen, and which had no previous presence of drosophila or food. We placed ripe, cut fruit and germinated grains (rye, wheat) in separate wine glasses, in relatively similar amounts in each wine glass. Then, we let the drosophila free into the library. After their release, we gave them completely free will to land absolutely wherever they wanted. Maybe out of shock, they first just flew around or landed on any available surface. Slowly and surely, however, they began to move in, on, and around the fruits and germinated grain in the glasses.

We then waited for 6 hours, and carefully, gently, trapped all the drosophila in the all glasses simultaneously using a closing device (a straight piece of steel with 6 flat pieces of plastic taped to it that sealed the top of each glass.) Andrei would then expertly count the amount of drosphila in each glass. Afterward, we’d slowly release the closing device… and wait another 6 hours before closing the glasses and counting again. We did this a total of 3 times; so once 6 hours after release, once 12 hours after release, and once 18 hours after release.

Below are the results for the counts we made:

As you can tell, the amount of drosophila that joined in on the party increased as time went on, so it’s hard to tell what relative amount of drosophila preferred which grain. This also makes standard deviation calculations difficult, as the numbers fluctuate significantly between counts.

Below is the same data, but with each count transformed into a percentage of the total drosophila counted for that count. So if there were a total of 100 drosophila counted on all fruits and grains during a round, and there were 5 drosophila counted on the apples, they’d make up 5% of all the drosophila.

This table shows the percentage of all counted drosophila that constituted each glass. All grain in “Organic Grain” was germinated. Percents 1, 2, and 3 refer to the relative percentages of the counts made in the same table above. The Average % refers to the percentage per glass. The 1 St. Dev. refers to how much these percentage values varied from one count to another. The final column on the right refers to the average percentage of drosophila that preferred some kind of fruit vs some kind of germinated grain.

Now that we have the counts as percentages, we can tell if there was a relative increase or decrease in the numbers of drosophila for each glass. What the data tells us is that the drosophila consistently preferred germinated grain, in similar percentages.

Below is a graph visualizing the “Average %” and “1 St. Dev.” columns in the table above:

As you can see in the graph above, drosophila significantly prefer germinated rye and wheat.

We then immediately switched out all the wine glasses for fresh, new clean ones (to remove any pheromones or indications of previous drosophila presence), and placed in newly cut pieces of fruit (cut from the same fruit as before however), and placed germinated pinto (gray) beans and white beans into separate glasses. We followed the same protocol as before; waiting 6 hours between counts and doing a total of 3 counts.

Below is the data we collected for the germinated beans.

This table lists the counts that were made:

This table lists the relative percentages of drosophila:

Below is a graph visualizing the “Average %” and “1 St. Dev.” columns in the table above:

This graph again shows us that the Drosophila significantly preferred the gray and white beans vs the ripe cut fruit.

Additionally, the drosophila were much more active and mobile in the glasses with germinated grain/beans than in the glasses without. We don’t really know what this means, but we think it’s interesting to point out.

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In conclusion, this tells us that:

     1. Drosophila melanogaster may possibly serve as a “living” detector of high quality, biologically active food

     2. Germinated grains and beans attract Drosophila significantly more than ripe fruits

     3. Germinated grain may have more enzymatic activity, “biological activity”, and “correct” microorganisms than freshly cut fruit

     4. Drosophila were much more mobile and active once trapped in the germinated grain glasses than in the fruit glasses

As a last addendum to this experiment, while we had our germinated grain out on display at the Zilker Gardens Festival, not only drosophila came by to inspect and take something from the grain, but bees and butterflies also visited. This makes sense for bees, as they need yeast and bacteria to help them ferment pollen and nectar into “bee bread”. Butterflies may be getting something they need from it as well!

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