Observing the Development
of Drosophila in Apple Juice Agar
1994 Woodrow Wilson Biology Institute
In this lab investigation you can easily see the development of the Drosophila fly. The Drosophila fly takes two weeks to develop from an egg to an adult. It goes through 4 stages: egg, 3 larval instars, pupa and adult. This lab is designed to allow you to observe the first two stages - the egg and the 3 larval instars. One day after an egg is laid, the first instar hatches. This instar soon goes through a molting during which it sheds its cuticle, mouth, and hooks. This produces a second instar which eventually also goes through a molting process producing a third instar. During the lab, you may see three different instars in your cultures. Be observant and differentiate the three different larval instars. If at the end of the observations you see a larva with a hardened, dark cuticle, this may be the beginning of the puparium. The fly will spend six days in the pupa before changing into an adult.
Directions for the Lab
- Sex flies from a culture provided by your teacher. Practice handling and sexing the flies. Separate out 3 - 5 females on an index card.
- Place the females in a Petri dish prepared with apple juice agar medium while they are still anesthetized.
- Leave the females in the Petri dish for 1 day at room temperature. During this time they will lay eggs. As the eggs develop you will be able to see the larvae through the transparent medium.
- After 1 day, release the adult females. Seal the Petri dish around the edge using tape or parafilm. Avoid opening the culture again because bacteria and fungi from the flies' bodies will be growing in your culture also.
- Observe the culture every day for 8 days using a stereo dissecting microscope. The clear medium will allow you to see the larvae moving and eating under the microscope. Look for all stages of growth: the egg and the three instar larvae. Refer to the information and/or drawings provided by your teacher.
- Keep a log of your observations, noting any changes in the number of larvae, size, appearance, or color.
- At the end of the lab, return your cultures to your teacher for proper disposal.
- This lab serves as an excellent way to introduce Drosophila handling techniques and the sexing of flies before doing genetic crosses. It can serve as a bridge between the study of development and genetics. Teachers will need to give thorough directions for this part of the lab. (See "Itsy and Bitsy Discuss Dinner.")
- Introduce the life cycle of the Drosophila fly to the students before the lab or early in the first few days. Diagrams and pictures would be helpful. A good resource is: Carolina Drosophila Manual, ISBN 0-89278-027, pages 7-8 and figures 4-6 (available from Carolina Biological Supply Company, 1-800-334-5551).
- The Drosophila culture can be an old one of any hardy variety - as long as there are gravid females.
- Prepare the apple juice agar plates before the lab. They can be stored in the refrigerator.
- Once the cultures have started, you may keep them in the refrigerator if needed to slow the growth of contaminating organisms. Unfortunately, this will also slow the growth of the flies. If the Drosophila larvae are not growing, put the cultures at 21 degrees Celsius.
- After the completion of the lab, leave the cultures taped. Autoclave and dispose of them properly. If Autoclave is not available, a bleach solution may be used as an alternative method of disposal.
The Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281