Feeding Test: Assessment of Feeding Preferences in Drosophila melanogaster

This protocol is an excerpt from Bovier et al., Methods to Test Endocrine Disruption in Drosophila melanogaster, J. Vis. Exp. (2019).

1. Feeding Assay

NOTE: This assay is recommended to test if the presence of the selected EDC in the medium could affect feeding of flies.

1. Put 15 young flies in vials containing Cornmeal medium (CM) supplemented with different concentrations of the selected EDC and a coloring food. Allow flies to feed on the media for 1 day.
   NOTE: For example, use red dye no. 40 (1 mg/mL).
2. Put 15 young flies in vials containing CM supplemented with the solvent alone and a coloring food for control. Allow flies to feed on the media for 1 day.
3. Anesthetize individually each group of flies with ether.
   1. Transfer flies of each group to a cylindrical glass container (etherizer) with a funnel inserted into the open end, inverting the vial over the funnel and gently tapping the two containers together to make the flies fall into the etherizer.
      NOTE: The funnel will prevent them from getting out of the etherizer.
   2. Knock flies down by gently tapping the etherizer on a soft surface, such as a mouse-pad, and quickly replace the funnel with an ether-soaked cotton and gauze plug.
   3. Wait about 1 min until the flies fall to the bottom and stop moving.
      NOTE: Do not exceed the time or the flies will die.
4. Put immobilized flies under a stereo-microscope and compare the abdominal coloring of each treatment group with respect to the control group.