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

We studied pollen flow and reproductive success in two different-density stands of Cistus libanotis, a self-incompatible species. The pollinator spectrum comprised Hymenoptera, Coleoptera, and Diptera, but their relative frequencies 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 factors indicate that Hymenoptera are the most effective pollinators and the major contributors to C. libanotis reproductive success. Nevertheless, considering the insect species, a dipteran, the syrphid Eristalis tenax appears to be more effective than some Hymenoptera on the basis of its C. libanotis-pollen carrying ability. Fluorescent dust dispersal indicated that the neighborhood area for pollen dispersal was different among stands and could change during the flowering season. Considering the reproductive output over the flowering season, differences in pollinator spectrum and in pollen flow among stands did not affect the reproductive success of C. libanotis individuals; both fruit and seed set were similar among stands.