How ‘loyal’ are honey bees in pollination of target crops?

Apis mellifera, the western honey bee, is a major pollinator of commercial crops. Crop producers rent honey bee hives that are placed within their fields during bloom. However, honey bees are not considered to be the most efficient pollinators in some crops, such as red clover (Trifolium pratense; Fabaceae) and blueberry (Vaccinium spp.; Ericaceae) due to the presence of a long corolla tube and the need for buzz pollination, respectively. While the economic impact of using commercial honeybee hives in these crops has not been fully quantified, producers of red clover seed and blueberries typically rent 1-5 hives per acre. The objective of this study was to evaluate foraging behavior of honey bees in these two crops by examination of pollen loads on workers returning to hives. Pollen samples were collected once a week by placement of pollen traps on commercial hives located in blueberry and red clover fields in the Willamette Valley of western Oregon. Samples were collected prior to, during, and after bloom. A subset of 50 pollen loads from each of the samples was processed using acetolysis, and identified to plant family. These results show that honey bees were frequently foraging on species of Rosaceae, Limnanthaceae, Brassicaceae, Anacardiaceae and non-target Fabaceae rather than target crops even during periods of full bloom. The results of the pollen analyses and implications of this research will be presented.