Taste Preference Assay: A Method for Measuring Feeding Behavior in Drosophila

- To perform the taste preference assay, use a chamber, for example, a Petri dish divided into equal sections. If measuring the choice between two solutions of different tastes, label one in red and the other in blue using tasteless food coloring agents. Then place equally spaced drops of each solution along the edge of the dish across alternating sections.

Now add anesthetized and previously starved flies to the middle of the chamber and cover the dish. Perform the experiment in the dark to exclude potential color bias, and incubate at 25 degrees Celsius over a set time period. When given a choice between two solutions, more subjects prefer to consume solutions whose taste is more attractive, for example, sweet, while avoiding aversive options such as bitter solutions. Stop the experiment by moving the chamber to a freezer.

To measure feeding behavior and taste preference, compare the number of flies with different colored abdomens. In the example protocol, we will see a demonstration of the taste preference assay that measures the choice between various sucrose solutions.

- To begin the experiment, saturate a cotton ball with water at the bottom of a standard fly vial. Next, collect flies in sets of 100 animals on a CO2 pad, and then add the flies to a prepared vial. Use a cotton ball to secure the vials closed. Then, place the vials on their side in an environmentally-controlled incubator. Prepare the control tastant of 1 millimolar sucrose by combining 10 microliters of 100 millimolar sucrose solution, 13 microliters of red food coloring, and 977 microliters of water.

Next, prepare the experimental tastant of 5 millimolar sucrose. Then, create the assay chambers by obtaining a 100 millimeter by 15 millimeter plastic Petri dish and placing three 10 microliter drops of control tastant as close to the edge of the plate as possible at the 12 o'clock position. At the 3 o'clock position, place three 10 microliter drops of experimental tastant as close to the edge of the plate as possible. Place another three drops of the control tastant at the 6 o'clock position. Then place another three drops of the experimental tastant at the 9 o'clock position.

Next, empty one vial of 100 starved flies onto a CO2 pad just long enough to anesthetize all animals. Brush the animals into the middle of a prepared assay chamber and cover it with the dish lid. Place the assay chamber into an opaque cardboard box. Then label the outside of the box with the condition and genotype being tested. Move the entire setup into an incubator. After two hours, place the assay chambers, still contained within cardboard boxes, directly into a negative 20 degrees Celsius freezer until they are ready for quantitation.