Tech Tip: Fly Pad Fluorescence

Background – Fly Pad Fluorescence

Fly pad fluorescence can sometimes be a problem for researchers. At the 2018 Drosophila Conference in Philadelphia a scientist told us that he sometimes had trouble sorting his fluorescent flies because of background fluorescence from the fly pad itself. He recommended that we make a non-fluorescent fly pad. Rather than re-invent the wheel, I walked over to the Genesee Scientific (Flystuff) booth and talked to Ken Fry, the proprietor. I learned that Genesee already offers a black fly pad as an alternative to the customary white pad, but he did not know the fluorescence characteristics of either. I offered to test the relative fluorescence of the white and black pads, and he graciously sent me a package of each. (For anyone who has read this far who doesn’t know what a fly pad is and would like to find out, read the brief description at the end of this article.)

Alternative flypad surfaces from Genesee Scientific


Method

We investigated the fly pad fluorescence with all of the NIGHTSEA excitation/emission combinations for the stereo microscope and documented the results with a microscope camera and also with an Ocean Optics fiber optic spectrometer.


Results

To the eye it was clear that there was significantly less background fluorescence from the black fly pad surface than from the white surface.

The images below show the fly pads side by side under a stereo microscope under white light and fluorescing with excitation by Ultraviolet, Violet, Royal Blue, Cyan, and Green light, viewed through the matching NIGHTSEA barrier filter.

The graphs below show the relative fluorescence emission, as viewed through the barrier filter, for the five excitation sources.


What is a fly pad?

A fly pad is a working surface that Drosophila (fruit fly) researchers use for observing or sorting adult flies under a stereo microscope. Flies are maintained in stoppered vials with a food source on the bottom. If you let adults out of the vial they will do what flies are wont to do and fly away, which is fine for the flies but not a desirable outcome for science. Researchers anesthetize the flies in the vial with carbon dioxide (CO2), then tip the sleeping flies onto the fly pad. The pad is porous and is mounted on top of a box that is connected to a source of CO2. The CO2 seeping up through the pad maintains the flies in a state of restfulness.


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