In south Florida, the rough-leaf velvetseed, Guettarda scabra, is limited to fragments of the endangered pine rockland habitat. Its flowers exhibit traits typically associated with attraction of nocturnal hawkmoths (Sphingidae), although they are abundantly visited by diurnal lepidopterans. These observations question whether the sphingophilous nature of this species represents actual dependence on nocturnal visitors for sexual reproduction. A previous study found diurnal pollination in G. scabra; however, the results may have been skewed by extensive plant manipulations. To address this, we conducted a more comprehensive investigation to re-examine the role of diurnal visitors in the plant’s reproduction. We evaluated the relative contribution of diurnal and nocturnal flower visitors to female reproductive success of G. scabra in its natural habitat. We selectively exposed flowers to these visitor groups and identified all the lepidopteran visitors observed. We found that plants exposed exclusively to nocturnal visitors exhibited significantly higher fruit-set than those only exposed to diurnal visitors, whose fruit-set was minimal and equivalent to that of plants never exposed to visitors. These findings indicate that nocturnal visitors are essential for successful sexual reproduction of G. scabra. Our field observations revealed that at night, flowers of G. scabra are visited by the hawkmoth Xylophanes tersa, suggesting a specialized pollination system in which hawkmoths are effective pollen vectors of this plant. Contrary to earlier conclusions, we demonstrate that flowers of G. scabra are exclusively pollinated by nocturnal moths, despite more frequent legitimate visitation by diurnal lepidopterans, which therefore act as nectar and pollen thieves.
