Many plants show obvious floral adaptations to attract and facilitate pollination by nocturnal visitors. Many of these flowers also receive frequent diurnal visits, yet little is known about how these different visitors contribute to plant reproductive success. We studied the pollination biology of Manfreda virginica to measure the relative contribution of nocturnal and diurnal visitors to seed set, and test to what extent floral characters and visitation rates predict contribution to seed set. The pattern of nectar and pollen production indicated that M. virginica is adapted primarily to nocturnal pollination. Out observations of natural populations of M. virginica during two field seasons indicated nocturnal visitors consisted of medium sized moths and larger hawkmoths. The primary diurnal visitors were large bees. The results of exclusion experiments showed that diurnal pollination resulted in significantly less seed set than nocturnal and open pollination despite the frequency of diurnal visits. Visitor behavior and timing of anthesis appear to contribute to the reduced impact of diurnal visits to plant reproduction. These results suggest that while diurnal pollination contributes less to plant reproduction in some years, it may be important when considering the evolution of nocturnal pollination systems.