果蝇的饲养与保存

Drosophila fly food contains essential components: sugar and yeast, plus sterile water, soy flour, yellow cornmeal, agar for texture, corn syrup, and propionic acid to inhibit mold and bacterial growth. These ingredients are combined, heated, stirred, and distributed into vials using a pump. After filling, vials are plugged with cotton, wrapped, cooled at 4°C, and sterilized via autoclaving.

A container must be changed when approximately half of the pupae have eclosed, or left the pupal casing. To identify when this occurs, hold the container up to a light source and inspect the pupa—clear casings indicate eclosion. Flies are then transferred to vials with fresh media via a process called flipping flies, ensuring the new food is free from cracks, mold, or bacterial contamination.

Flipping flies is the preferred bulk transfer method. First, gently tap the vial on the counter to knock flies off the sides. Quickly remove the stopper and invert flies into a new container rapidly. This speed prevents flies from escaping, being crushed by the stopper, or loose flies entering the vial. Before flipping, always inspect media for integrity—flies cannot survive on cracked or contaminated food.

Chilling and carbon dioxide are the primary anesthetization methods. Chilling involves placing cultures in a -20°C freezer for 8-12 minutes or directly on a frozen surface. Carbon dioxide is preferred because it does not cause acute mortality or researcher danger. The CO2 system uses a tank, needle-tipped tube for vials, and a CO2 plate for microscopic analysis, allowing gentle fly manipulation with a brush or forceps.

Normal storage conditions for flies are 25°C and 60-65% relative humidity. Incubators control the environment and can hold hundreds of vials and bottles. Proper labeling and documentation are essential to maintain the integrity of fly lines and experiments. Vials typically contain 50-100 adults, while bottles house 300-600 adults for larger cultures.

Fly diet can be supplemented with specific reagents to study particular biological processes. For example, all-trans-retinal can be added to the food by melting it and incorporating the reagent, enabling light-activated ion channels to function. This allows researchers to observe specific responses, such as escape behavior, when flies are exposed to blue light that activates the channel and induces measurable behavioral responses.

Negative geotaxis is the fly's natural response to move upward against gravity. Researchers study this behavior using a power tower machine that continually rises and drops, challenging flies to climb. Performance is measured using a Rapid Iterative Negative Geotaxis assay, or RING assay, where flies in empty vials are tapped and distances climbed are recorded by camera to assess activity levels.