Orchard studies clearly demonstrated that sexually mature female and maleRhagoletis pomonella(Walsh) respond positively to the odor of fresh-picked apples of susceptible varieties in a stage suitable for oviposition and larval development. Evidence suggests that the nature of the flies' response is one of attraction (in the loose sense of the word). No response was detected to the odor of fresh-picked fruits of a nonsusceptible apple variety or a nonhost species, choke cherry (Prunus virginianaL.). We discuss the potential utility of the unidentified attractive component(s) of the fruit odor in development of improved devices for monitoring fly populations and new, integrated methods of population management.