How to Breed Fruit Flies

"Anesthetize them with carbon dioxide. Sort males from females. Use virgins.

“Make sure you use flies that haven’t bred before,” says Christina Lim, 28, who spent years breeding and feeding fruit flies at the NASA Ames Research Center near Mountain View, Calif., in preparation for the insects’ 2017 flight to the International Space Station. Data from those flies showed that spaceflight caused serious structural and biochemical changes to their hearts.
Female fruit flies become sexually active eight to 10 hours after they hatch. To control the mating process, you need to use virgins. First, anesthetize them all with carbon dioxide. Sort their sleeping bodies on a flat surface under a microscope using a small paintbrush. Males are smaller and darker. Virgin females are pale and slightly shinier; Lim says they look almost wet, “like a puppy after it’s born.”
In many ways, fruit flies resemble humans at a cellular and genetic level. The insects have long been an essential part of genetic research, and populations are bred continually in scientific labs around the world. After you sort them by sex and other biological characteristics (like white or red eyes), put them back in closed bottles or vials to wake up. (Don’t leave them anesthetized for more than 20 minutes.) The vials should contain several weeks worth of food. Recipes vary, but Lim mixed ingredients like agar, soy flour, malt extract, yeast, molasses and cornmeal. Let the food harden in the container before adding the flies. “Don’t put the flies in while it’s still sticky,” Lim says.
When you’re ready to make more flies, anesthetize your flies again and add healthy males in with virgin females (usually in a one-to-three ratio). Fruit flies like to multiply; females can lay up to 100 eggs a day. For the spaceflight, the breeding had to be timed just right. Lim and the NASA Fruit Fly Lab team removed the adult flies before launch so that the vials contained just eggs, allowing for a new generation of winged creatures hatched in orbit.
The very first animals in space were fruit flies blasted in a rocket from the future White Sands Missile Range in 1947. Lim figures she has bred millions of flies. Such careful insect husbandry has given her a deep appreciation for an insect most people see as a pest. “I know how much information you can get from them,” she says."