The generalist pollination system and reproductive success of Calluna vulgaris in the Upper Ardenne

Although specialist pollination systems are often thought to be the outcome of selection, wide evidence exists for generalization within plant-pollina tor interactions. We studied the pollination system and reproductive succes s of Calluna vulgaris (L.) Hull over 3 years in an Upper Ardennes site in B elgium. A wide variety of insect visitors was recorded including Hymenopter a, Diptera, and Lepidoptera. Relative abundance of families and species of visitors varied markedly among years except for bees. Bumblebees and honeyb ees were the most efficient pollinators at the study site. Syrphid flies, m ainly large ones, acted as important co-pollinators because of their high r elative frequency. Calluna pollen was also dispersed by wind, and insect-ex clusion experiments demonstrated that wind pollination contributed to repro ductive success. Following open pollination, fruit set was high, ranging fr om 82.0 to 97.2% and independent of sampling location. Mean seed number per fruit was less than maximum potential seed number and varied strongly amon g sampling locations. We discuss this pollination system (generalist insect and wind) in terms of the ecological and geographical success of the speci es.