The white, tubular, fragrant flowers of Guettarda scabra (Rubiaceae), rough-leaved velvetseed, open in the evening and are visited by hawkmoths (Sphingidae). Flowers last for one day, and recent observations reveal that butterflies also visit these flowers. Hawkmoths hover over the flower and lower their proboscis into the corolla to collect the nectar. Butterflies land on the petals before inserting their proboscis and may transport pollen on their bodies as well as their mouthparts. We conducted an experiment to determine the importance of each of these guilds for pollination of G. scabra. We excluded day-time visitors from some inflorescences and night-time visitors from others on the same plants (with two controls: some open all the time and some bagged all the time). We maintained this regimen during the entire flowering period of the selected inflorescences over two months and compared fruit set among the treatments. The control-open inflorescences and the night-open inflorescences had substantially higher fruit set than day-open and control-bagged inflorescences. Mean fruit set of day-open plus night-open inflorescences approximated that of control-open inflorescences, and although the fruit set of day-open flowers was small, it differed from bagged controls. Fruit set in G. scabra is determined almost entirely by hawkmoths, but butterflies may be useful as secondary pollinators. As plants flower in months when afternoon and evening rains can extend into the night, morning pollinators may be important. This study provides additional evidence that diurnal pollinators can contribute to the reproduction of predominantly nocturnal pollinated plants.
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Vol. 86 • No. 1