Tests were performed between 12:00 and 16:00 hrs. Using forceps, we transferred flies by their hook and fixed them to a magnetic clamp, which was then attached to a rack. This treatment established free movement of the flies’ tarsi and proboscis and was a modification from a previously described PER assay Scheiner 2014Scheiner 2004, itself derived from similar assays developed for honeybees Jr 1998Scheiner 2014Scheiner 2004, itself derived from similar assays developed for honeybees Jr 1998. The modifications were designed to prevent unnecessary stress and pressure on the abdomen of the flies. A group of six to eight flies was tested in parallel. A filter paper soaked with sucrose solution was presented for 5 s to all six tarsi but not the proboscis. Seven different concentrations (0, 0.1%, 0.3%, 0.6%, 1%, 3%, and 30%) were presented in series with an inter-stimulus interval of 80 s. The proboscis extension response was recorded. Finally, the proboscis was stimulated by 30% sucrose solution. Flies not responding to this last stimulation or responding to the first stimulation (water only) were discarded from the analysis.