Charlotte St. Romain
1991 Woodrow Wilson Biology Institute
|6 flies||source of CO2|
|6 2 inch insect pins||styrofoam block (to hold flies)|
|very sticky glue or wax||forceps|
|distilled water||Petri dish|
|6 triangle-shaped strips of paper cut from the corners of index cards|
|paper discs (made from filter paper by using a hole punch)|
|test solutions (different concentrations of sucrose, lemon juice, etc.)|
In order to test a fly's responses, it must first be "captured". The most effective way to do this is to anesthesize the flies with CO2 only long enough to keep them from escaping. After they have been exposed to the gas long enough to stop moving, carefully clip one of the wings in case they begin to wake-up too soon. Obtain 1 fly at a time from the CO2 source, place a drop of glue on the paper point, press the point onto the fly's back between its wings so that the paper point is parallel to the fly's body. Run each of the 6 pins through the broad end of a paper point and move the paper towards the blunt end of the pin until it is about 3/8 inch from the blunt end. (see diagram). Once the fly is immobilized, stick the pin into the styrofoam block so that the fly's feet are pointed downwartd. Repeat for all 6 flies.
Before beginning the actual testing procedure, clean the flies' tarsi (feet) by exposing them to a dish of distilled water. Begin the testing by using forceps to offer a distilled water-soaked disk to each fly's legs, letting them hold the disk and drink until they no longer extend their mouthparts. Repeat this procedure immediately after each solution used. Dip a paper disk into each solution for each of the 6 flies, beginning with the most dilute solution, which is contained in tube # 1. Offer a disk soaked with each test solution to all flies. Repeat the procedure using tubes in the following sequence: 2, 3, 4, 5, and finally 6. Observe the behavior of each fly based on the following responses:
Record the response of each fly for each solution tested. If the fly responds at level 1, remove the paper disk immediately before the fly has a chance to drink much of the fluid. Flies which respond at levels 2 or 3 should have the disks taken away after 10 sec. Always, after removal of the disk, you will want to "clean the flies' palates" by giving them a fresh disk saturated with distilled water. Rinse forceps as well. If the observer notes that the fly is no longer responsive to the solutions, it is advisable to test fresh flies. Then try to determine what will make a fly reject sugar. It is also possible to test other substances that have the same effects on the flies, such as artificial sweeteners, alcohol, caffeine, and insect repellent. Combine data collected by all groups in the class and determine the lowest concentration of sucrose that flies respond to.
Dini, M. and Harris, J. (1991). "Taste Reception in Flies." Animal Physiology Update Workshop Manual. LSU Baton Rouge.
Oakley, B. and Schafer, R. (1978). "Feeding Behavior: Taste Reception in Flies." Experimental Neurobiology: A Laboratory Manual. The University of Michigan Press.
Pentz, Lundy (1989). "Perception and Behavior." The Biolab Book (Second edition). The Johns Hopkins University Press. Baltimore.
Houseflies (Musca spp.) can be used, but blowflies (Phormia spp.) are suggested. Obtain about 40 pupae or larvae per group per laboratory period. They can be obtained from entomology departments, researchers, and biological supply houses. Order pupae which have just pupated. Place them on a thin layer of slightly moistened vermiculite in an enamel pan. Cover with more vermiculite and moisten slightly. Do not let the vermiculite dry out. The pan should be placed in a fly cage screened on four sides and one end. Tacked around the perimeter of the other should be a cloth (old piece of nylon panty hose works fine) which is long enough to twist and tie securely with a string. When you are ready to remove flies, insert your hand and trap the flies into a small bottle. Place a petri dish containing dry table sugar in the cage along with a jar of water inverted on two pieces of filter paper in another petri dish. Food and water sources are essential for the flies as soon as they emerge. It will take a period of approximately two weeks for all the flies to emerge. If the adults need to be kept longer, store them at 4 degrees C in a container covered with a plastic bag. Deprive the flies of food (but not water) for 48 hrs. at room temp. prior to testing. Testing two or more days after mounting on paper strips provides even better results. Feed the flies before placing them in cold storage (4-10 degrees C) until using them again.