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Drosophila
Nature Bulletin No. 576 October 17, 1959
Forest Preserve District of Cook County
Daniel Ryan, President
Roberts Mann, Conservation Editor
David H. Thompson, Senior Naturalist
DROSOPHILA: THE FRUIT FLY
Have you noticed any tiny flies in your kitchen or around the fruit
bowl? They are so small that they come through ordinary screens into
homes, stores and restaurants. From midsummer until the killing frosts
of autumn, swarms of them cluster wherever ripe or fermenting fruit is
exposed -- outdoor markets, tomato canneries, garbage cans, melon
patches, vineyards, and apple, pear or peach orchards. At this season,
hordes of them are found around cider mills where they breed in the
cakes of pressed apple pulp or pomace. A few adults and young survive
the winter in basement drains and other protected places with food and
warmth.
These Fruit Flies are strongly attracted by the sour or yeasty odors that
come from rotting fruit and other fermenting substances. Yeast is the
main food of both adults and young. Because of these preferences they
are also called Vinegar Gnats and Pomace Flies. Dozens of species are
known, all much alike in habits and appearance. By far the most
common and best known is Drosophila melanogaster, the one reared in
bottles on a large scale for school use, research, and as food for small
aquarium fish, captive spiders and other insect-eaters.
Fifty
years ago, the fruit fly was discovered to be an almost ideal
laboratory animal for the study of heredity -- usually called genetics.
Among its advantages is the fact that they breed the year around, and
twenty or more generations a year are easily obtained. Each pair of
parents can produce a hundred to several hundred offspring in a small
milk bottle with some fermenting banana or specially prepared food.
They are clean, inexpensive to rear, require little care, and a hundred of
these bottles can be kept in the schoolroom or laboratory.
Over the years, geneticists have found hundreds of different heritable
variations or mutations in Drosophila and have traced in detail their
methods of inheritance. Breeding experiments between pure-bred
pedigreed races of fruit flies with different eye colors, body colors,
wings, and dozens of other characteristics, are widely used by students
in schools and colleges for exciting studies of heredity Leaflets
describing the methods for rearing fruit flies and for carrying out some
of these experiments may be had free of charge from the General
Biological Supply House, 8200 South Hoyne Avenue, Chicago 20,
Illinois.
The adult wild fruit fly, seen through a hand lens or low-power
microscope, has large bright red eyes and a tan-colored head and
thorax. The abdomen of the female is crossed by dark lines. That of the
male has a black tip. In addition, each of his front legs bears a
conspicuous jet-black "sex comb" having several teeth. By their second
day of adult life, these flies are sexually mature. Then the male begins
his "courtship dance". Facing the female, he shifts from side to side,
flirts his wings up and down, and does his best to show off.
Against a dark background the elongate white eggs are barely visible to
the naked eye. Within two days, at room temperature, tiny white
glistening larvae hatch. These feed constantly and reach full size in
about six days. Then they form into straw-colored pupae, shaped like
little wheat grains, which rest for five more days before the adults
emerge.
Consequently, students can repeatedly observe the entire life history of
fruit flies, learning about insect biology, as well as heredity, from them.
That mote in your eye may be a fruit fly.
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Update: June 2012
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