Abstract
Although the Drosophila melanogaster (fly) model is a popular platform for investigating diet-related phenomena, it can be challenging to measure the volume of agar-based food media flies consume. We addressed this challenge by developing a dye-based method called Consumption-Excretion (Con-Ex). In Con-Ex studies, flies consume solid food labeled with dye, and the volume of food consumed is reflected by the sum of the dye inside of and excreted by flies. Flies consumed-excreted measurable amounts of FD&C Blue No. 1 (Blue 1) and other dyes in Con-Ex studies, but only Blue 1 was readily detectable at concentrations that had no discernable effect on consumption-excretion. In studies with Blue 1, consumption-excretion (i) increased linearly with feeding duration out to 24 h at two different laboratory sites, (ii) was sensitive to starvation, mating status and strain, and (iii) changed in response to alteration of media composition as expected. Additionally, the volume of liquid Blue 1 consumed from capillary tubes was indistinguishable from the volume of Blue 1 excreted by flies, indicating that excreted Blue 1 reflects consumed Blue 1. Our results demonstrate that Con-Ex with Blue 1 as a food tracer is a useful method for assessing ingestion of agar-based food media in adult flies.
Highlights
The fruit fly (Drosophila melanogaster) has emerged as a powerful model for investigating the effects of diet on both physiological and disease-like states
Several related ideas influenced the method we developed: (1) many inexpensive food dyes are commercially available; (2) when flies consume food medium labeled with dye, accumulation of dye inside flies plateaus over time because dye intake is quickly balanced by excretion of the dye as waste[31]; (3) dye in excreted waste should accumulate over time within vials in which flies are housed; and (4) at the conclusion of a feeding experiment, the sum of the dye found inside flies and the dye excreted from flies should reflect food intake
Major experimental steps in Con-Ex studies include (i) placing adult flies in empty food vials containing a single removable feeder cap that contains solidified food medium labeled with dye (Fig. 1A,B); (ii) allowing flies to consume food from the feeder caps and excrete waste in the vials for prescribed periods of time (Fig. 1C); (iii) at the conclusion of food exposure, extracting the dye inside flies (Internal dye, INT) and the excreted dye (ExVial, ExMedium) (Fig. 1D); (iv) quantitating the dye in these extracts via spectrophotometry (Fig. 1E); (v) converting the dye absorbance to volume via interpolation from standard curves of pure dye (Fig. 1F); and (vi) calculating the consumed-excreted volume of media (Fig. 1G)
Summary
The fruit fly (Drosophila melanogaster) has emerged as a powerful model for investigating the effects of diet on both physiological and disease-like states. It can be challenging to determine the volume of media flies consume under routine housing conditions[30] This lack of clarity greatly undermines the causal connections that can be drawn between diet, dietary intake and physiological measures in the fly model. A limitation of these two other approaches is that it is unclear if proboscis extension into food media or the proportion of flies feeding on food media equates with the volume of media consumed Another method called FlyPAD determines feeding behavior in individual flies based on their interaction with solid food medium[34]. The most promising approach for measuring solid food intake in flies under typical housing conditions described to date quantitates the consumption of dietary media labeled with a radioactive tracer. The Con-Ex method should be suitable for assessing consumption of solid food media in flies in a wide range of laboratories, especially those in which the use of radioactive food labels might be challenging
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
