Culturing Techniques and Handling of Flies

Drosophila, like other animals, requires an optimum temperature for its survival, growth, and breeding (20°–25°C). The temperature around and above 31°C makes the flies sterile and reduces the oviposition; it may also result in death. At lower temperatures, the life cycle is prolonged and the viability may be impaired. The routinely used food media for the maintenance of Drosophila is “cream of wheat agar” medium.

The ingredients of this media for preparing culture bottles are as follows:

• Distilled water – 1000 mL
• Wheat flour (rava) – 100 gm
• Jaggery – 100 gm
• Agar agar – 10 gm
• Propionic acid – 7.5 mL
• Yeast granules.

Wheat flour and jaggery are boiled in distilled water until a paste is formed. To that, agar agar and yeast granules are added after cooling. Propionic acid is added to avoid fungal infection of the medium.

Heat-sterilized bottles should be used for preparing cultures. Similarly, sterilized cotton has to be used to plug the bottles. As the condition of the medium deteriorates with time, the flies have to be transferred from the old to new culture medium at least once in 3 weeks.

Whenever the flies have to be analyzed, either for routine observations or for experiments, they have to be anaesthetized to make them inactive. The procedure is to transfer the flies from the media bottle to another empty widemouthed bottle, referred to as an etherizer. The mouth of this bottle is covered with a stopper and sprayed with ether. It takes about a minute to anaesthetize the flies. After this, the flies are transferred to a glass plate for observation under a stereo zoom microscope. If the etherized flies revive before the completion of the observation, they have to be re-etherized using a re-etherizer (ether-soaked filter paper fitted in a petriplate, which has to be placed over the flies on the glass plate). The overetherized flies will have their wings and legs extended at right angles to the body, and such flies are considered to be dead.

The flies should be handled with a fine painting brush. In the process of handling the flies, care should be taken not to damage them. The flies should be discarded after observation.