Transferring flies from one vial to another Flies should be transferred every 10 to 14 days. Students should maintain a backup culture of their flies, and the instructor should maintain backup stock cultures of all fly strains. There are two basic ways to transfer flies when forming new cultures. One requires no anesthetizing but quick hands.
A) Place a funnel in the mouth of a fresh culture vial that already has media added. In the old vial (the one with flies in it), gently tap the flies down by softly tamping the vial on a soft surface, such as a mouse pad. The flies will fall to the bottom and remain there for a few seconds (no more than that!), enough time to quickly take the plug off the vial, invert it into the funnel, and gently tamp, together, the two vials to force flies down into the new vial.
B) An alternative way is to put the flies in the freezer for about 8 minutes. This will cause the flies to fall into a state of stupor. After placing a funnel on the new vial, invert the vial with motionless flies into the funnel. This is not as much fun, but you won’t have any flies flying around the classroom.
Sexing flies It is pretty easy to tell males from females, and with a bit of practice, students will become confident of their ability to do so. Notice that males are generally smaller and have a darker and more rounded abdomen. The coloration of the abdomen is the easiest to recognize. In addition, males have tarsal sex combs on their first pair of legs. These are black and very distinctive but can only be seen under relatively high magnification. With a bit of practice, by looking at the abdomen, students will become proficient in accurately sexing flies. Sexing flies is critical when making crosses, so be sure students are confident in identifying the difference between the sexes. For students to feel comfortable sexing flies, give or have them obtain 25 or more mixed-sex flies and allow them to sort the flies into two piles, male and female. Other students in the group and the instructor should verify the sorting. Each member of the group should be able to sex flies.