To study 30 human generations, we would take 500 years or more. But by using the fruit fly, we can study 30 generations in a single year. In a few hours, a number of female fruit flies can lay enough eggs to produce a thousand new adults, all emerging on the same day. They lay their eggs only in fruit that has begun to rot or decay. When the young are born, they feed on the fermentation which the decaying fruit produces.
The fruit flies can be studied with the naked eye and surgical operations can be performed on them under a microscope, Most of our present knowledge of heredity has been gained from the study of fruit flies!
There are actually two different kinds of fruit flies. The Drosophila which is harmless. And the Mediterranean fruit fly, which looks somewhat like a housefly with orange and black markings. The Mediterranean fruit fly is one of the most destructive pests.