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The Effect of Citrus Oils on Fruit Flies

1994 Woodrow Wilson Collection


Fruit flies can be a nuisance to humans. Oddly enough, citrus oils have been shown to be toxic to the fruit flies. The question that arises is how could citrus fruits be toxic to fruit flies when fruit flies live on fruit? This was the basis of a research project for high school student Catherine Shih of Milburn High in New Jersey. The literature revealed that fruit flies live and reproduce within citrus fruits. They lay their eggs within the peel and between oil glands. If, however, the eggs are laid in the oil glands, they die. These citrus oils are toxic to other insects such as other flies, ants, fleas, wasps and crickets.

Materials and Methods:

Wild type fruit flies, Drosophila melanogaster
Instant Drosophila media
Fly vials(25ml) or disposable bottles(100 mls) (oils are toxic)
Vial plugs (cotton)
Four citrus fruits: fresh or prepackaged oils
  • lemon (5g per 20 ml of food)
  • grapefruit (5g per 20 ml of food)
  • lime (5g per 20 ml of food)
  • orange(5g per 20 ml of food)
  • Drosophila anesthetizer
    Fly Nap
    index cards
    camel hair brushes
    marking pencils
    dissecting scopes

    Part I:Determining Effectiveness of Four Citrus Fruits (per group of students)

    1. (If prepackaged oils are not available) Prepare the citrus blends by taking 5g of finely diced peels, blending with 20mls of prepared instant Drosophila media (1:1distilled water to instant medium). Label the prepared bottles.

    2. If prepackaged oils are available, for prepared oil, add 1 drop per 100 mls of prepared food.
    3. Prepare instant food in each container according to the package directions. (Add appropriate fruit oils to food mixture.)

    4. Prepare the following groups of vials: Each vial should contain 10 female flies and 10 male flies.

      A. 2 control tubes
      B. 2 grapefruit
      C. 2 lemon
      D. 2 lime
      E. 2 orange

    5. In Trial 1 you will observe the effects of oils on the viability of parental generation by counting the number of flies that survive in the various mediums A-E. Suggested time is 7 days.

    6. At the end of 7 days, count live adult flies and dispose of them into a morgue.

    7. In Trial 2 you will observe the effects of oils on the viability of the second generation by counting the number of surviving flies after the allotted time period has elapsed.

      Suggested time an additional 7 days.

    8. At the end of this phase count the F1 adults. Dispose of them and the cultures.


    Student handout

    Part II: Results

    TABLE 1: P VIABILITY AFTER 7 DAYS
    Treatment Number Living Interpretation
    A. Control
    B. Grapefruit
    C. Lemon
    D. Lime
    E. Orange

    TABLE 2: F1 VIABILITY
    Treatment Number Living Interpretation
    A. Control
    B. Grapefruit
    C. Lemon
    D. Lime
    E. Orange

    Part III: Analysis

    1. Determine the percentages of viable P for each treatment and rank from high to low for effectiveness as a toxin.

    2. Determine the number of viable F1 flies for each treatment and rank from high to low for effectiveness as a toxin.

    3. Compare the effects of the treatments on adults (P1) to the F1. Offer reasonable explanations for differences based on the life cycle of the fruit flies.

    4. How might other variables relate to experiments you propose?

    5. If oranges had no defenses against fruit flies, the oranges would be wiped out. If the defense mechanisms of oranges against flies are so severe, then all the fruit flies die or would avoid oranges. A stable evolutionary relationship has resulted between oranges and fruit flies. What evolutionary advantages do the fruit flies give the oranges? Suggest and explain.

    TEACHER NOTES

    The Effects of Citrus Oils on Fruit Flies

    1. Except for citrus oils, all supplies are available from Carolina Biological 1-800-334-5551. Prepared oils are somewhat difficult to find, but are available from local bath/beauty shops. This ought to be a telephone search: make sure the oils are not synthetics.

    2. Bottles for culturing the flies are recommended. See the exercise for collecting earlier in this module for the type of bottle and the fruit fly medium.

    3. Another phase of the project could be to steam distill the oil after using a fruit or garlic press to extract juices from the peels. If a steam mantle is not available try the sand bath as shown below.


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