Mating behavior of the melon fly, Dacus cucurbitae COQUILLETT, was observed in a field cage. As a potential rendezvous site, a coral tree (non-host plant) with 60 leaves and 30 attached host fruits was placed in the cage. Several major characteristics of melon fly mating behavior in the field cage proved essentially the same as those observed in small laboratory cages in previous studies. However, considerable new information was obtained in the field-cage study : (1) Mating behavior was initiated principally on the tree leaves (bottom surface), with a lesser amount on the cage wall; (2) Very few males were located on the fruit and no matings were initiated there; (3) Both sexes concurrently moved from the tree to the wall 20-30 min before dusk, following which males returned to the tree (on leaves), when they emitted sex pheromone attractive to females-receptive females then returned to the tree and copulated with males; and (4) Our observations strongly suggested the existence of lek formation on tree leaves by the males.