Abstract
Aggressive behavior of the western cherry fruit fly studied both under laboratory and field conditions indicates that males are extremely territorial, especially in the field, where they do not tolerate the presence of another fly on a cherry unless the invader is a mating partner. Under confined laboratory conditions, the sense of territoriality was markedly reduced. Aggressive behavior in this insect included a wing jerking display, head-on collision, and "boxing" (fight involving prothoracic legs).