Name: ________________________________________________
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AP Lab 12: Fruit Fly Behavior
Introduction
Drosophila melanogaster, also known as the fruit fly, has been studied by scientists for just over 100 years. Now it’s
your turn to study not their genetics, but their behavior. What environmental factors trigger a fruit fly response?
Background
The fruit fly can be found throughout the world and feeds on ripe or rotten fruit and the fungi growing on rotting fruit.
Despite Drosophila’s small size, fruit fly studies have enlightened many areas of scientific understanding. Drosophila
exhibit many interesting physical and behavioral characteristics. Its genome has been sequenced, its physical traits have
been documented and mutated, and its behavior has been well chronicled. Because of all of their scientific applications,
Drosophila are considered a model organism for geneticists and behaviorists.
Drosophila obtained its name based on observations of its characteristics. Fruit flies follow circadian rhythms that
include sleeping in the dark and emerging as adults from pupa in the early morning. The latter behavior gave rise to the
name Drosophila which means “lover of dew.” The explanation for the species name melanogaster is based on physical
features – Drosophila have a black abdominal area.
Physical Characterization
Like all insects, Drosophila have three main body parts – the head, the thorax, and the abdomen
(see Figure 1). The major structures of the head of the wild-type fruit fly are the large red
compound eyes, the olfactory antennae, and the mouth. Between the eyes are two antennae
the fly uses to sense odors. The mouth is a proboscis – the fly lowers it to suck up food like a
vacuum cleaner. The thorax has six legs, two wings and, on the dorsal (top) side, a number of
long dark bristles.
Figure 1: Drosophila
Sexing Flies
Identification of sex is most reliably done by examination of the genital organs with the aid of magnification. The
external reproductive organs of both the male and the female are located on the ventral-posterior part of the abdomen.
The male genitalia are surrounded by heavy, dark bristles which are not present in the female (see Figure 2, Part A). This
characteristic is quite distinct even in a fly that has just emerged from the puparium.
As flies age, the posterior portion of the abdomen becomes very dark in males and considerably lighter in females. The
tip of the abdomen is rounded in males and more pointed in females. Generally, male fruit flies tend to be smaller than
females but this is not a reliable characteristic to sort the sexes. Females have stripes on every segment of their
abdomen. Males have shorter abdomens, and the last few segments of the abdomen are solid black. Males also have a
set of brown anal plates on the ventral (bottom) side of the abdomen. The front legs can also be used to distinguish
sexes. There are sex combs on the front legs of the male fly (see Figure 2).
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Transferring Flies between Vials or Culture Tubes
Sometimes it becomes necessary to transfer flies from one vial to another. Reasons can vary from moldy media to
simply wanting to increase stock. To transfer flies from one vial to another, first tap the vial containing the flies down so
that the adults are gathered near the bottom. Quickly remove the foam stopper and invert the tube on top of the
second vial containing fresh media. Note: A funnel may be placed in the receiving vial to reduce chances of the flies
escaping. Tap the vials on the table so that the flies fall into the new vial and then quickly stopper the vial (see Figure 3).
Behavior Terminology
A taxis (from Greek taxis meaning to arrange) is an automatic, oriented movement towards or away from a stimulus.
Animals move in response to a variety of stimuli. A chemotaxis is the movement in response to a chemical stimulus.
The organism may move towards or away from the stimulus. Think about how an organism benefits by responding to
chemicals differently in their environment. Phototaxis is a protactic response to light. A geotactic response is a
movement in response to gravity.
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Experiment Overview
Determine fruit fly behavior and preferences for certain environmental factors over others by giving them options within
a choice chamber.
Pre-Lab Questions
1. Fruit flies tend to lay eggs on fruit that is not yet ripe. This is an example of behavior that has been naturally
selected to improve the survival of offspring. Why is it they might choose unripe fruit?
2. Fruit fly media is susceptible to bacterial and fungal infestation. Why?
Materials
Drosophila melanogaster, 30-40
Dissection pins, 2
Cotton balls, 6
Choice chamber tube
Foam plugs for choice chamber, 35-44 mm diameter
Permanent marker
Ruler
Preparation of the “Choice Chamber”
1. Using a ruler, determine the distance that is half-way across the transparent plastic cylinder, approximately 6”
from the end.
2. Using a permanent marker, draw a line at this half-way point as shown in
Figure 4.
3. Label one side of the chamber “A” and the other side “B.”
4. To test different substances, place 5 drops of water on a cotton ball. Add the
solution being tested to the cotton ball. Note: Do not add so much solution
that it drips down the side of the choice chamber.
5. Insert a dissection pin through the center of the cotton ball.
6. Attach the cotton ball to the foam plug as shown in Figure 5. Note: Solid pieces of fruit or
other food may be attached directly to the foam plug with a dissection pin.
Procedure
Part A. Baseline Activity
1. Using the transferring procedure as described in the Background section, carefully transfer
10-20 fruit flies into the behavior chamber.
2. Hold the chamber vertically. Which direction are the fruit flies traveling?
3. Turn the chamber over and wait 30 seconds. Observe the flies again and note their direction of travel.

Describe observations regarding the direction the fruit flies moved in the chamber. What possible explanation
might there be for this behavior?
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Part B. Opportunities for Inquiry
In this portion of the activity you will investigate fruit fly movement using a choice chamber that exposes fruit flies to
different substances. Flies are very common in households. What types of foods or condiments found in households
might attract or repel the fruit fly? Design an investigation to determine commonalities in substances that attract and
repel fruit flies, their reaction to light and gravity. Directions for building the choice chamber are listed on page 3.
1. Consider the following questions while reflecting upon your knowledge of taxis and Drosophila.
a. How does the age of the fruit fly relate to the flies’ tendency to be attracted or repelled to it?
b. How might Drosophila react to dilute acids or bases?
c. Is one taxis stronger than another taxis?
2. Plan, discuss, evaluate, execute and justify an experiment to test a question regarding taxis and Drosophila.
a. Decide upon one question your group would like to explore (you are not limited to the questions listed
above).
b. Develop a testable hypothesis.
c. Discuss and design a controlled experiment to test the hypothesis using the behavior chamber.
d. List all materials required and research their safety precautions that will be implemented to keep
yourself, your classmates and your instructor safe during the experimental phase of the laboratory.
e. Determine how to collect and record data.
f. Determine how the data will be analyzed to test the hypothesis.
g. Review your hypothesis, safety precautions, procedure and proposed data analysis with your instructor
to be approved prior to beginning the experiment.
h. Once the experiment and analysis are complete, evaluate your hypothesis and justify whether or not the
hypothesis was supported by your data (NOT PROVEN CORRECT).
i. Identify possible errors and how they impacted your results.
j. Make suggestions for a revised or new experiment to modify or retest your hypothesis.
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