Entomophilous pollination of raspberry, red currant and highbush blueberry in a mountain area of Friuli-Venezia Giulia (North-eastern Italy)

In a mountain area of Friuli-Venezia Giulia region (north-eastern Italy), pollinators of cultivated raspberry, red currant and highbush blueberry were studied for three years in a commercial orchard. During the whole flowering period the insect species and the number of pollinators visiting the flowers at different times of the day were observed. The main groups of pollinators visiting the flowers were sampled at different times of the day and at different phases of flowering. Before the flowers opened, some branches (or shoots) were enclosed in netting bags to stop the entrance of insects. In this way fruit from branches with open pollination could be compared with that from covered branches, thus measuring the differences in fruit set, fruit drop, weight, diameter and number of seeds. On raspberry the most active pollinators were honeybees (Apis mellifera), bumblebees (Bombus spp.) and hoverflies (Volucella spp. and Blera fallax). Blueberry flowers were visited mostly by bumblebees (Bombus terrestris and B. pratorum) as the bell-shaped corolla prevents short tongue pollinators (such as honeybees and solitary bees) from reaching nectar glands. Entomophilous pollination of red currant was limited by nectar and pollen competition from wild species flowering at the same time; however, this crop was visited above all by the Hymenoptera of the genus Andrena spp. and Halictus spp. and by hoverflies. In raspberry and blueberry, even if the flowers are considered self-fertile, the effect of entomophilous pollination showed higher fruit set, lower fruit drop and greater fruit size. On red currant few pollinators were observed and no apparent effect on fruit set, drop and weight of fruits was noted comparing branches enclosed or not in netting bags.