Figure 1. The preference for ethanol containing food is independent of nutrient value.

(a) Canton-S (CS) flies were analyzed in the CAFE assay for a preference for liquid food containing ethanol at the indicated percentages. CS flies display a significant preference for food containing 5%, 10% and 15% ethanol. (b) The daily food consumption of CS flies over a four day period was determined for the indicated liquid foods that also contained 5% yeast extract. In this experiment, the flies were allowed access to only one kind of food if without ethanol in food, or were tested in the standard two choices CAFE assay. Although CS modulates the amount of food consumed per day based on the sucrose content, they did not alter food consumption based on ethanol concentration. (c) The caloric value consumed by each fly daily for each food substrate was determined. In this assay, CS flies balanced the energy intake from sugar, but failed to make a similar adjustment to calories provided by ethanol, because the daily energy intake from each kind of ethanol-containing food was more than these of three kinds of non-ethanol food. (d) The ability of CS flies to utilize ethanol as an energy source was examined through a survivorship assay. CS flies fed with 0.7% ethanol survive significantly longer than completely starved flies, but significantly shorter than flies fed with 0.89% sucrose. Since 0.7% ethanol contains similar caloric content as 0.89% sucrose, the shorter survival time on ethanol as a food source compared to sucrose suggests that Drosophila cannot use a majority of the calories present in ethanol for sustenance. Data are means ± S.E.M. “N.S.” means no significance. ***P<0.001.