See this paper, for example: https://www.nature.com/articles/srep20938

"Drug Feeding

Caffeine (Sigma-Aldrich) was mixed into melted sucrose/agar food at a concentration of 0.5 mg/ml for all experiments except for the dose-response experiment where 0.2, 0.5 and 1 mg/ml were used. L-DOPA (Tocris) was mixed into melted sucrose/agar food at a concentration of 3 mg/ml."

You can also get some interesting insights into feeding patterns when using bioluminescent flies: Method Monitoring fly feeding behavior and timing by beetle lucifer...

Michael Koksharov Thank you Michael for stopping by and responding to my query. It is a great help while I was searching for a protocol for reference, though I have used during my masters, I just did not have the citation and record of the scientific detail of the chemical (caffein) I used.

Sunil Kumar Birua

In Drosophila research conducted in India, commonly used caffeine is laboratory-grade anhydrous caffeine, often sourced from reputable chemical suppliers such as Himedia, SRL (Sisco Research Laboratories), or Merck. Researchers typically prefer caffeine in powder form due to its ease of handling, uniform dissolution, and consistent dosing when mixed with fly media.

To utilize caffeine in Drosophila media, it is advisable to first dissolve the caffeine powder in distilled water or ethanolto create a stock solution. The concentration can vary depending on the study design, but a common range is 0.1–5 mg/mL. Ensure the caffeine is fully dissolved by stirring or using mild heat if necessary, and then allow it to cool before mixing it with the fly food (usually a cornmeal or agar-based medium) once the food has cooled to about 50°C to prevent degradation or evaporation of volatile solvents.

Crystalline caffeine is chemically identical to the powdered form but may take slightly longer to dissolve. Therefore, for practical laboratory use, powdered caffeine is typically preferred for its faster solubility and ease of storage and weighing. Always filter sterilize the solution if required, especially for sensitive experiments, and store the stock in an amber container to avoid degradation by light.