The CApillary FEeder (CAFE) Assay: A Method to Track Food Consumption and Preference in Drosophila

- To prepare for the Capillary Feeder, or CAFE assay, insert graded or marked glass capillaries filled with colored, liquid food, bottom end first, through the pipette tips on top of a preassembled experimental vial. Ensure the capillaries are securely placed at the same height and are not in contact with the apparatus.

Mark the starting level of the meniscus in each capillary. Then house the vials in a temperature-, humidity-, and light-controlled environment for the duration of the experiment while replacing capillaries as needed. During the CAFE assay, mobile flies are unrestrained and have free access to the bottom open end of the micropipette. Flies feed voluntarily as they extend their proboscis and intake the liquid, reducing the medium inside the capillary.

To track food consumption and preference for a set time period, record the descent of the meniscus from the starting mark to the level at the end of that period from qualifying capillaries. In the example protocol, we will see the CAFE assay with the assembly modified to achieve reduced evaporation from the liquid-filled capillaries.

- Carefully remove the pipette tip that is closing one of the outer openings, and insert