Honey bee (Hymenoptera: apidae) pollination of rabbiteye blueberry Vaccinium ashei var. 'Climax' is pollinator density-dependent

In a 2-yr field study, mature orchard plants of rabbiteye blueberry (Vaccinium ashei Reade variety 'Climax'), plus potted pollenizers ('Premier') were caged with varying densities of honey bees (0, 400, 800, 1,600, 3,200, 6,400, or 12,800 bees plus open plot) during the bloom interval. The rate of legitimate flower visits tended to increase as bee density increased within a range of 400 6,400 bees; there were more legitimate visits in cages with 6,400 bees than in those with less than or equal to1,600 bees. Similarly, within a range of 400-6,400 bees there was a trend for a corresponding increase in fruit-set with means ranging from 25.0 to 79%. Fruit-set was higher in cages with 6,400 or 3,200 bees than in those with less than or equal to800 bees. Regression analyses showed that fruit-set increased linearly with the rate of legitimate bee visits. Mean weight of berries was unaffected by bee density but varied significantly between years. Within a range of 0-3,200 bees/cage the average seeds per berry tended to increase with increasing bee density; there were more seeds in open plots than in cages with 12,800 honey bees or less than or equal to1,600 bees. Sucrose content ranged from 12.1 to 16.7% and fruits tended to have more sugar in cages with lower bee densities. Speed of ripening tended to be higher in cages with higher bee densities. Earlier work has shown that the effectiveness of Apis mellifera L. as a pollinator of rabbiteye blueberry is variety-dependent. Our data indicate that the effectiveness of A. mellifera is also bee density-dependent.