Reproduction Of Drosophilia Melanogaster

Introduction
 
I will be conducting an experiment to figure out whether or
not the amount of medium in a vial will affect fruit fly
reproduction. During the experiment I will be counting the
number of fruit flies at one week intervals and observing
the following: 

1. are a greater number of fruit flies in the vials with a
larger amount of medium,
 2. are a greater number of fruit flies in the vials with
lesser amount of medium, 
3. is the number of fruit flies in the vials the same,
regardless of the amount of medium.
 
There is a great importance in this experiment. During the
1970's and 80's, the Mediterranean fruit fly invaded the United States. This fruit fly drills its sharp ovipositor
into ripe plants, and then deposits her eggs there. After
about a week or two these eggs develop into larva, which
burrow through the fruit, damaging the fruit and making it
unable to be sold. This badly damaged the United State's
agricultural economy. Soon after, worldwide quarantines
were put on the rapine fruit fly (Foote, 1993). Therefore,
the importance of this experiment is to determine whether
or not the amount of food available for the fruit fly
increases their reproduction. I will ascertain this by
keeping the red-eyed pomace fly, Drosophilia Melanogaster,
(Mediterranean fruit flies are illegal to keep in the
United States) in varying heights of medium, 3/4 inches and
1 1/2 inches. 

If there are more fruit flies in the 3/4 inch vials, then
we know that the less food equals more fruit flies. If
there are more fruit flies in the 1 1/2 inch vials then we
know that more food equals more fruit flies. Or, if there
are equal amounts of fruit flies in both heights of vials
then we know that it doesn't matter how much food there is,
there will still be the same amount of fruit flies. By
using this information, farmers may be able to stop further
fruit fly invasions. 

Fruit flies belong to the order Diptera and constitute the
family Tephritidae (Webster, 1988). They are two-winged
flies, whose larvae feed on fresh or decaying vegetable
matter. The Drosophilia Melanogaster lays its eggs on
decaying fruit and therefore has no need for a sharp
ovipositor and doesn't cause agricultural destruction
(Encarta, 1995). 

The reproductive cycle of Drosophilia Melanogaster, from
egg to larva to adult, lasts about two weeks (Highnam,
1963). It all begins in the ovary. Each ovary has sixteen
ovariolees, which are egg assembly lines (see Figure 1A).
Each ovariole has a germarium, which is the place egg
chambers develop (see Figure 1B). Each egg chamber has a
large nucleus called an oocyte, around fifteen nurse cells,
and 1000 follicle cells, which protect and nourish the egg.
During the development of the egg chamber an eggshell,
called the chorion, forms (see Figure 1C). On the exterior
of the anterior part of the egg two dorsal extensions form.
These will assist the fruit fly embryo in breathing once
the egg is fertilized. Just below the two extensions is the
operculum. This is the exit for the embryo, once it has
reached the larval stage. Underneath the operculum is the
micropyle, which is the entryway for the sperm (see Figure
1D). 

Once the egg chambers are fully developed they leave the
germarium and move posteriorward in linear order. Most
developed to least developed, with the aid of rhythmic
muscular contractions from the ovarian wall and end up the
uterus (see Figure 1B) (Bate and Arias, 1993).
 
Figure 1
 
If the egg isn't fully developed while sexual intercourse
is occurring between the male and female fruit flies, then
the sperm will be kept in a minute space in the forward
portion of the uterus (Engleman, 1970). Once the egg is
fully developed and ready to be fertilized the sperm are
released. After the egg has been fertilized the female
deposits the eggs on the rotten fruit or vegetable
(Kaulenas, 1992) (see Figure 2). Within around a week, a
larva crawls out of the egg and burrows through the rotten
matter and begins to molt. It will molt twice while inside
the medium (Sonnenblick, 1965). Four days later, the larva
crawls out of the medium, attaches itself to a dry surface
and forms into a pupa. After three more days an adult or
imago D. Melanogaster will emerge (Ward's lab, 1994).
 
Figure 2
 
The objective of my experiment is to determine whether or
not the amount of medium (food) in a vial affects the
reproduction of fruit flies. My hypothesis is that there
will not be a difference in the quantity of fruit flies. I
believe that here will not be a difference because the
fruit flies cannot eat 1 1/2 inches of medium, let alone
3/4 of an inch of medium. They will not need that much
medium, and therefore will technically have the same amount
of medium.
 
Materials and Methods
 
The first step involves the preparation of the fruit fly
medium. To make 7.5cm of medium, place a 113.4gram. vial,
base down, next to a ruler and add 3.75cm of Ward's instant
Drosophilia medium into the vial. Do this by dipping a
spoon, does not have to be sterile, into the jar of Ward's
instant Drosophilia medium and putting into the vial. After
each spoonful of medium, tap the vial until the medium is
relatively flat. After there is 3.75cm of medium in the
vial, add 3.75cm of distilled water into the vial (see
Figure 1).
 
Figure 1
 
Repeat these steps for three other vials. To make 15cm of
medium, perform the same steps but use 7.5cm of instant
medium and 7.5cm of distilled water. After all of the vials
have medium in them, 4 vials with 7.5cm of medium in them
and 4 vials with 15cm of medium in them, allow them to sit
overnight to let the medium soak up the distilled water. 

The second step in my experiment was to introduce the fruit
flies into the vials containing the medium. First, place
one vial of wild type fruit flies or yellow white fruit
flies into the freezer until all fly motion has ceased
(around 5 minutes)(see Figure 2).
 
Figure 2
 
Remove the vial from the freezer, uncap it, and turn it
upside down and let the fruit flies out onto a white
surface. Working as quickly as possible put 20 live fruit
flies into a vial with 7.5cm medium by moving them
carefully with a camel's hair brush. The fruit flies are
dead if they carry their wings vertically. If the fruit
flies are alive they carry their wings horizontally. If
there aren't enough flies for that vial, use flies from
another vial until there 20 in that vial. If there are
extra flies, use them in another vial. After there are 20
fruit flies in a 7.5cm vial put that vial aside. Repeat
these steps except put 10 fruit flies in a vial with 7.5cm
medium in it. Repeat these steps for the vial with 15cm
medium in it. Repeat the preceding steps for the
yellow-white fruit flies. The vials have 10 fruit flies and
others have 20 fruit flies to see if the fruit flies need a
higher or lower population to breed more successfully.
After all 8 vials have the according number of fruit flies
and height of medium in them (4 vials with 7.5cm medium and
4 vials with 15cm medium in them) label them with the
amount of fruit flies in them, the height of the medium,
and the date the flies are put into medium.
 
At weekly intervals the flies should be put into the
freezer, counted on a white surface, and returned to their
vials. Record the number of fruit flies in vial on a chart
that is similar to Figure 1 (also make one for the
yellow-white fruit flies). One chart for the Wild Type
fruit flies and one for the Yellow-White fruit flies.

 Drosophilia Population Count 
 Wild Type (+) Fruit Flies 
 Date: Week 1 Week 2 Week 3 Week 4 
Week 5 Week 6 
 7.5cm media 
 5 pr 
 10 pr 
 15cm media 
 5 pr 
 10 pr 
 
Figure 3 

Continue this for eight weeks, 4 generations of fruit
flies, always making sure the intervals between counting is
the same. The vials should be stored in a safe place that
does not receive direct sunlight for long periods of time
and has a constant temperature of around 39 degrees Celsius
such as styrofoam vial holders I used (see Figure 4).
 
Figure 4
 
A thermometer should be kept by the fruit flies and checked
every day. It is does not hurt the fruit flies to be
exposed to total darkness.
 
Figure 5-some necessary materials. From left to
right:Styrofoam vial holder, instant drosophilia medium,
magnifying glass, 113.4 gram vial cap, styrofoam plug,
113.4gram vial, camel hair brush and fruit flies
 
Results
 
In this experiment to find whether the amount of medium
affects Drosophilia Melanogaster reproduction, the data
collected reveals that the amount of medium does affect
Drosophilia Melanogaster reproduction. Chart 1 shows the
exact data. In the vials with 3/4" medium the Drosophilia
Melanogaster population drops slightly between the first
and second week, then as the first new generation hatches
the Drosophilia Melanogaster population jumps upward. The
fly population then drops between the third and fourth
weeks, except in the case of the vials with 5 pairs of
Yellow-White fruit flies. By the fifth week the 3/4" fruit
fly population is dwindling, and by the sixth week all of
the fruit flies have perished. In the vial with 1 1/2"
medium there was an immediate jump in the 5 pair
Yellow-White fruit flies and a very slight drop in fruit
fly population from first week to the second week. With the
Wild-Type fruit flies their population continued to rise
until the fifth week, when a slight population drop
occurred. From the fifth week to the sixth week the
population continued to rise. With the 5 pair Yellow-White
fruit flies their population their population rose from
Week 1 to Week 6. With the 10pr Yellow-White fruit flies
their population continued to increase nonstop from Week 1
to Week 6.

 Drosophilia Population Count 
 Wild Type (+) Fruit Flies 
 Date: Week 1 Week 2 Week 3 Week 4 
Week 5 Week 6 
 3/4" media 
 5 pr 10 9 53 21 9 0 
 10 pr 17 13 49 35 19 0 
 1 1/2" media 
 5 pr 6 22 44 47 41 68 
 10 pr 14 12 41 56 43 61 
 
 Yellow-White Fruit Flies 
 Date: Week 1 Week 2 Week 3 Week 4 
Week 5 Week 6 
 3/4" media 
 5 pr 9 8 19 32 1 0 
 10 pr 11 10 36 22 11 0 
 1 1/2" media 
 5 pr 6 15 28 29 43 45 
 10 pr 15 13 32 37 46 54 

Chart 1
 
Drosophilia Population Graphs