Why does one choose a burger over a carrot? How much is it possible to change that choice? What can Drosophila tell us about it?

I wanted to study Drosophila spontaneous behaviour regarding their food preferences and how malleable it is, so I can then try to condition it – and one should notice that those are “preferences” and therefore not neutral CS to begin with, as usual.
For that I used wild type Drosophila starved for 24 hours.
Drosophila likes the sweetness and the nutritional value of sucrose and does not like the bitter taste of quinine. Vinegar is a well-known attractant and benzaldehyde a well-known repellent.
To test the food preferences I simply add different food colouring to the food, test the flies in Petri dishes with alternated 10µL food drops and then, after 2h at 25°C and without light, I freeze them and count the number of flies based on the colour of their abdomen:

Here I present my first results:

(n = number of trials, each using 40 flies.)

As an illustration, here I have a short video showing a few flies during their initial food exposure:

And here the results with food in the presence of odours:

(The odours were placed in a small piece of filter paper inside the Petri dish.)

Next I would like to see if I can change their preferences (using these foods or sucrose vs fructose, etc.) through conditioning (as in the Garcia effect). Suggestions are welcomed.