Entomophily of the cloudberry (Rubus chamaemorus)

Cloudberry (Rubus chamaemorus L.), a dioecious perennial plant of boreal circumpolar distribution, is greatly prized for its berries. We crossed two treatments, pollinator exclusion and supplementary hand-pollination, to determine i) the relative importance of insects as pollinators, ii) if pollinator activity was a limiting factor for the sexual reproduction of the plant, and iii) the relative contribution of diurnal vs. nocturnal visitors to pollination. The activity of natural pollinators resulted in 97.5 and 88.5% fruit set, along with 76.7 and 62.5% seed set in 1998 and 1999, respectively. When insects were excluded, fruit-set dropped significantly to 18.4 (1998) and 12.8% (1999) and seed-set to 5.4 (1998) and 5.0% (1999) showing the importance of mid- and large-sized insects as pollinators. Natural levels of insect activity were sufficient to ensure complete pollination in both years as supplementary hand-pollination did not significantly increase either parameter in plots where pollinators had free access. Nocturnal insects may serve as pollinators (fruit-set = 41%), although they were less effective than diurnal pollinators (fruit-set = 93%).