Pollinator attendance and reproductive success in Cistus libanotis L. (Cistaceae)

We studied pollen flow and reproductive success in two different-density st ands of Cistus libanotis, a self-incompatible species. The pollinator spect rum comprised Hymenoptera, Coleoptera, and Diptera, but their relative freq uencies at the flowers differed between stands. The pollen loads carried by insect visitors were from a considerable number of plant species (up to 11 species) apart from C. libanotis. Hymenoptera showed the highest activity rate and the highest flower visitation rate and carried by far the highest number of both total pollen grains and C. libanotis pollen grains. These fa ctors indicate that Hymenoptera are the most effective pollinators and the major contributors to C. libanotis reproductive success. Nevertheless, cons idering the insect species, a dipteran, the syrphid Eristalis tenax appears to be more effective than some Hymenoptera on the basis of its C. libanoti s-pollen carrying ability. Fluorescent dust dispersal indicated that the ne ighborhood area for pollen dispersal was different among stands and could c hange during the flowering season. Considering the reproductive output over the flowering season, differences in pollinator spectrum and in pollen flo w among stands did not affect the reproductive success of C. libanotis indi viduals; both fruit and seed set were similar among stands.