A Simplified Method of Drosophila Culture for the Classroom

Abstract

Many high school and college instructors have attempted to use the common fruit fly, Drosophila melanogaster Meigen, in the elementary biology classroom, usually to illustrate some simple Mendelian ratios. Many have also given up after one such attempt and advised others to avoid the beasts. The purpose of this article is to describe and illustrate some simplifications of technique and equipment which have, in the author's experience, eliminated many objections to the use of Drosophila in the general biology class. One of the greatest barriers has been the preparation of the food media. The difficulty has resulted from the very refinement of the techniques used in advanced college and research laboratories. The teacher who has had a laboratory course in genetics has been taught that these animals must be fed on a special formula. Those who have prepared Drosophila media know that making a baby's formula is simple by comparison. The synthetic food media, while they do have a legitimate place, are out of place in the general biology laboratory. Any teacher, or student, can make first-rate fly food in a few minutes with only three ingredients, all of which are available at any grocery. One needs: 1. A banana, preferably barely ripe and with no soft spots that could contain fly larvae; 2. A five-cent envelope of dried, granulated yeast; 3. A box of facial tissue. Select the glassware to be used (more on this point later), making sure that it is clean. Peel the banana, discard the skin, and mash to a soupy pulp. Spoon the banana mash into the glassware, to a depth of l2' to 34?. Make a wad of tissue large enough to occupy about one-fourth of the bottom of the container, and push it into the banana mash at one side. The paper soaks up excess moisture and provides a resting place and site for pupation. Then shake a few grains of yeast, not more than 3 or 4 per square inch of food area, on to the mash. A cotton plug in the mouth of the container completes the process. The result is a few containers of the most nutritious fly food available (Figure 1). Care should be taken in the selection of the bananas, for one fly larva in a soft spot could contaminate a carefully kept strain and render it useless. For most laboratory strains of flies the contamination would not be too catastrophic but would require careful attention to the strain for a couple of generations. Why isn't this method used in research laboratories? It is and has been used. It is the method generally used during the first few years of laboratory research with Drosophila. It is being used in research in genetics and