  Factors that mediate ethanol preference in Drosophila melanogaster are not
well understood. A major confound has been the use of diverse methods to
estimate ethanol consumption. We measured fly consumptive ethanol preference on
base diets varying in nutrients, taste, and ethanol concentration. Both sexes
showed ethanol preference that was abolished on high nutrient concentration
diets. Additionally, manipulating total food intake without altering the
nutritive value of the base diet or the ethanol concentration was sufficient to
evoke or eliminate ethanol preference. Absolute ethanol intake and food volume
consumed were stronger predictors of ethanol preference than caloric intake or
the dietary caloric content. Our findings suggest that the effect of the base
diet on ethanol preference is largely mediated by total consumption associated
with the delivery medium, which ultimately determines the level of ethanol
intake. We speculate that a physiologically relevant threshold for ethanol
intake is essential for preferential ethanol consumption.
