Enhanced UV-B radiation, flower attributes and pollinator behaviour in Cistus creticus: a Mediterranean field study

The aim of this investigation was to examine the reasons for the higher pollination success in Cistus creticus under enhanced UV-B radiation (Stephanou & Manetas 1998). Thus, a selected array of floral attributes as well as the frequency and duration of insect visits were studied in the field under ambient or ambient plus supplemental UV-B radiation, simulating a 15% ozone depletion over Patras (38.3° N, 29.1° E). Video-recording revealed two categories of visitors, i.e. true pollinators (bees) and nectar thieves. The frequency of visits to both control and UV-B treated plants was the same and independent of whether the UV-B tubes were on or off during video recording. UV-B radiation had no effect on gross floral morphology (petal surface area, number of pollen grains, stamens and ovules, optical properties of petals and stamens), yet nectary size was almost doubled. In addition, the duration of insect visits was significantly longer on UV-B treated plants, provided that the UV-B tubes were off during monitoring. The differences were abolished during the part of the day that the tubes were on, indicating that the insects were annoyed by supplemental UV-B radiation. These results are consistent with the nectaries producing larger quantities of nectar, which caused the insects to stay longer on flowers of UV-B treated plants and improved pollination success.