For F 1 seed production in Brassicaceae crops, cross-pollination between the two parental lines is vital and is dependent on the visitation behavior of insect pollinators. In a radish F 1 seed production field using cytoplasmic male sterility system, visitation behaviors of different pollinator species and seed productivity of the recipient line were investigated in three stages during the flowering. As a result, honey bees (Apis mellifera and A. cerana) selectively visited either of two lines, while syrphid flies (various flies belonging to Syrphidae) tended to visit both lines. Despite the few observations of pollinator movements between the two lines, all flowers had received cross-pollen grains a few days after flowering. But in the late stage of flowering, increased cross-pollination by syrphid flies appeared to lead to an increase in the amount of crosspollen grains deposited on the stigmas. The percentage of pod set and the number of seeds per pod varied among the three stages of the flowering. These variations might be caused by shifts in the amount of crosspollen grains deposited on the stigmas due to the pollinators' selective visitation behaviors. The selective visitation behavior of insect pollinators could potentially result in unstable F 1 seed production through the insufficient cross-pollination.