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
can lay up to 300 eggs/day.
In your journal, construct a drawing of
this life cycle, including what the eggs, larvae and one adult looks
females are able to lay eggs however they will be sterile.
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
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
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
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
At the end of this lesson you should be
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
5. Descriptions of the differences between male and female flies.
1. Tell the
difference between male and female flies
2. Be able to anesthetize the
3. Feel comfortable working
4. Be able to make new cultures
5. Know the appearance of a typical fruit fly