Comparing Apis Mellifera and Bombus spp. Pollination Efficiencies on Willamette Valley Blueberry Farms

Abstract

With global honeybee populations declining there is a concern for the reproduction of plants that rely on biotic pollination, most notably food crops. The purpose of this study was to monitor the behavior and population size of bumblebees (Bombus spp.) and European honeybees (Apis mellifera) on Highbush Blueberry (Vaccinium corymbosum) farms in the Willamette Valley, Oregon. We evaluated the effects of farm size and bloom time on the pollination efficiency of each species. To make our assessments, we observed their floral handling rates, defined as the number of flowers visited per minute by a single bee, and took population samples, by walking systematically-sampled transects on each farm. Floral handling rate for bumblebees and honeybees was proportional across our two primary variables, with honeybees pollinating an average of 3.5 flowers per minute and bumblebees pollinating 11.2 flowers per minute. Across all farms, honeybees had a total of 1746 counts while bumblebees had only 300, providing a ratio of 5.8:1. Although honeybees were more abundant than bumblebees, there was only an apparent relationship between population counts and bloom time. Data from floral handling rates and abundance counts during mid bloom showed honeybees were three times more abundant than bumblebees, however, bumblebees were more effective pollinators, as measured by bee efficiency rate. Overall, the study indicated the essential role of bumblebees in the pollination of Highbush Blueberry plants.