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Fly
lab
report
p
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2


ABSTRACT
To feed on materials that are healthy for them, flies (order Diptera) use taste
receptors on their tarsi to find sugars to ingest
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To do this, we attached
flies to the ends of sticks and lowered their feet into solutions with different concentrations
of these sugars
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The flies responded to sucrose at a lower concentration than they did of glucose, and they
didn’t respond to saccharin at all
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They didn’t feed on saccharin because the
saccharin we use is actually the sodium salt of saccharin, and they reject salt solutions
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INTRODUCTION
All animals rely on senses of taste and smell to find acceptable food for survival
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Studies of sensory physiology have often used insects as
experimental subjects because insects can be manipulated with ease and because their
sensory-response system is relatively simple (E
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Flies
are able to taste food by walking on it (Dethier, 1963)
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These traits enable them to
find necessary nutrition
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In this experiment we tested the ability of the blowfly Sarcophaga bullata to taste
different sugars and a sugar substitute, saccharin
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Because saccharin is also sweet tasting to
people, I expected the flies to respond positively and feed on it as well
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Then we made a dilution series of glucose, maltose, and sucrose in
one-half log molar steps (0
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01M, 0
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1M, 0
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We tested the flies’ sensory perception by
giving each fly the chance to feed from each sugar, starting with the lowest concentration
and working up
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We counted a positive response whenever a fly lowered its proboscis
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See the lab handout Taste Reception in Flies (Biology Department, 2000) for
details
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The threshold concentration required to elicit a positive response from at
least 50% of the flies was lowest for sucrose, while the threshold concentration was highest
for glucose (Fig
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Hardly any flies responded to saccharin
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the lab groups together, there was a major difference in the response of flies to the sugars
and to saccharin (Table 1)
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46, df = 8, p <
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Also, the response of two flies to saccharin was
not statistically different from zero (t = 1
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s
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Flies show a selectivity of response to sugars based on
molecular size and structure
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The threshold value of glucose was the highest in this experiment
because a higher concentration of this small sugar was needed to elicit a positive response
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It has been shown that flies respond better to alpha-glucosidase derivatives
than to beta-glucosidase derivatives (Dethier 1975)
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This might also be the reason why sucrose tastes so
sweet to people
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The sweetener people use is actually the sodium salt of saccharic
acid (Budavari, 1989)
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Two flies
did respond positively to saccharin, but the response of only two flies is not significant,
and the lab group that got the positive responses to saccharin may not have rinsed the flies































Fly
lab
report
p
...

Flies taste food with specific cells on their tarsal hairs
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The membranes located on the tarsi
are the actual functional receptors since it is their depolarization that propagates the
stimulus to the fly (Dethier, 1975)
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More specifically, a fly will reject food if the substrate fails to stimulate the sugar
or water receptors, stimulates a salt receptor, or causes a different message from normal
(e
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, salt and sugar receptors stimulated concurrently) (Dethier 1963)
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This selectivity is a valuable asset to a fly because it helps the
fly recognize potentially toxic substances as well as valuable nutrients (H
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Substances such as alcohols and salts could dehydrate the fly
and have other harmful effects on its homeostasis (Dethier, 1976)
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ACKNOWLEDGMENTS
I thank Prof
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LITERATURE CITED
Campbell, N
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, & J
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Reece
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Biology, 8th ed
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6


Francisco
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, et al
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The Merck Index
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, Rahway, NJ
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2000
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Biology 101 Laboratory Manual,
Hamilton College, Clinton, NY
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G
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The Physiology of Insect Senses
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, London
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G
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The Hungry Fly
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Dethier, V
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, & E
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1989
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Physiological Entomology 14:127-136
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The average number of flies in each lab group that fed from 0
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The mean + standard deviation is shown
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2 + 1
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8 + 2
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6 + 2
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2 + 0
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7


Fig
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Taste response curves of flies to different concentrations of the sugars glucose,
maltose, and sucrose
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2
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Glucose
is a monosaccharide and is shown as part of each of these molecules

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