Getting to know your flies!

Part 1: A first look

Obtain a culture vial from your instructor. Note the behavior of the flies in the vial. What is their general movement? Gently tamp the tube on a soft surface. Note what happens to the flies. What occurs if you turn the vial upside down? Do all flies behave in the same way? Look carefully at the flies with your naked eye. Can you see any differences between flies? What else do you notice?

Part 2: A closer look

You will need a magnifier or stereomicroscope to see some of the features.

Looking at your vial, identify eggs, larvae, pupa and adults. To see the eggs, use a stereomicroscope and look for small white ovals with what appears to be two hairs sticking out from the top. You should be able to see these on the surface of the media. In your journal, draw an egg and larvae. Remember to include the magnification in all your drawings.

Part 3: Life cycle of the fruit fly

The fruit fly life cycle:
Day 0: Female lays eggs
Day 1: Eggs hatch
Day 2: First instar (one day in length)
Day 3: Second instar (one day in length)
Day 5: Third and final instar (two days in length)
Day 7: Larvae begin roaming stage. Pupariation (pupae formation) occurs 120 hours after egg laying
Day 11-12: Eclosion (adults emerge from the pupa case). Females and females are sexual mature 8-10 hours after eclosion

·Females can lay up to 300 eggs/day.
·Virgin females are able to lay eggs however they will be sterile.

In your journal, construct a drawing of this life cycle, including what the eggs, larvae and one adult looks like.

Part 4: Parts of the fly: external anatomy

To take a closer look at your flies, you will need to anesthetize them.

Take your culture tube and place it in the freezer until the flies show no movement. Record how long it takes to immobilize them. Remember that if you leave the tube in the freezer too long you run the risk of killing the flies and larvae. Once flies are anesthetized, place on the ice/petri dish setup and place under the stereomicroscope. You should have 10-15 flies.

Look at several flies and note the general physical appearance. Note the three distinct parts to this fly (as in all insects/arthropods): head, thorax and abdomen. Look carefully at each body part, and using the outline as a template, draw features you see on each segment. Do not worry about which sex it is, yet. Even if you do not know the names of some of the structures, draw them in anyway.

Part 5: How to tell males from females

Abdomen: notice the coloration pattern on the dorsal (back) side of the abdomen. Look carefully at the banding pattern – note some flies are completely black in the last 1/5 of the abdomen, while others continue the striped banding pattern to the end. The solid black at the end are male, the others females.

Look at several male and female flies – describe other characteristics besides abdomen banding to distinguish between the two. It is very important that you are able to tell the difference between males and females in order to set up the correct crosses!

Write down your descriptions, including the one given (put into your own words!) on how to tell the difference between males and females. Make a drawing of each abdomen, detailing the differences in the genitalia.

After you finish your drawings, take about 20 flies and sort them by sex.

Mix the flies up and have a member of your group sort them by sex. After each member has done this, compare your numbers. Everyone must know how to sex flies. If you are having trouble, ask your instructor for help.

Part 6: Culturing flies

Obtain a fresh culture tube. If there is no media in the bottom, your instructor will tell you what to do next. Pour your anesthetized flies into the fresh vial, using the funnel, and then plug the top. Remember to label this vial with type of fly, today’s date and your name or symbol after you put them in the new vial.

You can do the same if the flies are not anesthetized. To do so, place the empty vial with funnel on a pad. Take the tube with the flies and gently tamp the bottom on a soft surface. All the flies will fall to the bottom. Quickly take the top off the vial and invert the vial into the funnel. Gently tamp the vial-funnel system on the soft surface so flies will fall to the bottom. Quickly invert the vial and plug both.

Place your cultures of flies as instructed by your teacher.

Part 7: Self assessment

At the end of this lesson your journal should contain:

1. Pages numbered after the table of contents
2. A drawing of the life cycle of Drosophila
3. A drawing and description of an adult fly showing the structures on the fly body
4. At least 5 questions you came up with written in the back of your journal.
5. Descriptions of the differences between male and female flies.

At the end of this lesson you should be able to:

1. Tell the difference between male and female flies
2. Be able to anesthetize the flies
3. Feel comfortable working with flies
4. Be able to make new cultures of flies
5. Know the appearance of a typical fruit fly

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