Additional Laboratory Notes for BIO 3001

© John H. Wahlert, 2 April 2010

Division Eukarya
Kingdom Animalia
Phylum Arthropoda
Class Insecta

Insect Life Cycle—Fruit Flies

examining fruit flies

The fruit fly, Drosophila melanogaster, has been a key laboratory organism in genetics research. In this laboratory exercise you will learn to identify morphological features of the wild type, to handle the flies in a manner that permits experimentation, and to observe an insect life cycle.

You will be given a vial containing many live, wild type fruit flies. They occupy a laboratory habitat vial that consists of a gelatinous food medium at the bottom, a structure for the flies to rest on, and a cotton plug that keeps the flies in but allows gas molecules of air to circulate. I you are performing a cross, you will also be given a vial containing flies of a different phenotype.

You must anesthetize the flies to observe their characteristics with a dissection microscope:

  1. Gently tap the vial so that flies are knocked to the bottom.
  2. Dip the bristled wand into Fly Nap. Push it past the stopper, and insert it into the via so that it is above the flies. Put the lid back on Fly Nap.
  3. Tip the vial at a slight angle so that the food is higher than the stopper, and the Fly Nap wand is above the flies. The flies will stop moving in about 4 to 5 minutes (if you do this for too long and the wings move vertically over the body, indicating that the flies are dead).
  4. Dump the flies out onto a white card, and examine them under a dissecting microscope. Use a soft brush to move them around.
  5. Observations:

    • All flies show typical insect body regions head with antennae, compound eyes (crimson colored in wild type fruit flies) and mouth parts, thorax with wings and legs, segmented abdomen. Note the bristles on the body and legs.
    • Obvious gender differences: Mature females are much bigger than males. Males have solid black pigmentation at the tip of the abdomen (genital area) and the tip is rounded, whereas in females the abdomen is striped throughout, and it is pointed. In males, the first tarsal (foot) segment of the anterior pair of legs has a dark set of bristles called a “sex comb,” which is believed to have a role in courtship (this is very hard to see with a dissecting scope).

      fruit fly femalefruit fly male
      fruit fly photos by Julia Sesina

    sorting fruit flies
  6. Use a soft brush to separate the pairs of flies that you chose to be the parents of the F1 generation (select 3 to 5 pairs).
  7. Place them on the side of a fresh vial containing food and resting structure. Be careful that they do not fall into the sticky food while they are anesthetized.
  8. Insert a stopper in the top of the vial.
  9. You may dump left over flies into the morgue—a bottle of alcohol.

In future laboratories you will observe the fruit fly life cycle—egg, larva, pupa, and adult—and record your observations of the process.


To prepare a culture vial for the next generation of fruit flies:

  • Put one scoop of flaked medium into a vial;
  • Slowly fill and depress the pump to wet the medium;
  • Wait for medium to gel;
  • Add a strip of paper towel on one side, so that the flies have a rough surface to walk on;
  • Insert stopper.

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Last updated 24 April 2010 (JHW)