Bee foraging behavior and pollinating activity on rabbiteye blueberry Vaccinium ashei Reade
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In this dissertation, based on research conducted in four years (2000 – 2003) at the University of Georgia, USA, are presented results of studies about bee foraging behavior on rabbiteye blueberry, an important commercial crop throughout the southeastern USA, interactions of honey bees (Apis mellifera L.) with carpenter bees (Xylocopa virginica (L.), and the use of honey bees as vectors of the biocontrol agent Bacillus subtilis (Ehrenberg) Cohn used to reduce the incidence of mummy berry disease. These results demonstrate that pollination efficacy of honey bees on rabbiteye blueberry was pollinator density-dependent. The data indicate that V. ashei var. ‘Climax’ responds positively to increases in honey bee density as measured by fruit-set, seed number, and speed of ripening. 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 to79 percent. This study suggests that rabbiteye blueberry is an important energetic resource for pollinators. Nectar standing crop and nectar production during 24 h were affected by age of flowers and increased significantly in flowers older than one day. Nectar standing crop varied as well over the blooming season. Average nectar volume per flower was 2.85 µl, with an average sucrose concentration of 29.45%. Following a 2-yr study conducted to assess how nectar robbing in honey bees affects fruit production in rabbiteye blueberry, it was concluded that under tent conditions the continuous presence carpenter bees results in nearly 40% incidence of A. mellifera robbery. This level of secondary nectar thievery does not reduce fruit-set but does reduce the number of seeds per berry. On average, honey bees spent more time and energy handling flowers during legitimate visits than during robbing, suggesting that an energetic advantage exists for honey bees that engage in secondary nectar thievery in V. ashei. Further this study confirmed the ability of honey bees to vector the biocontrol agent B. subtilis to blueberry flowers and suggests that application of Serenade (commercial formulation of B. subtilis) via hive-mounted dispensers is a promising strategy to reduce the potential for transmission of mummy berry disease when honey bees are used as blueberry pollinators. Overall this research increases our understanding of pollinating efficacy and behavioral interactions of bee visitors in rabbiteye blueberry.