|Abstract or Summary
- Managed honey bee (Apis mellifera L.) colonies are important pollinators of many cultivated crops. Honey bee colony declines averaging 30% annually in the United States for the past 7 years have caused significant concern and hence have been a topic of intensive investigation. These declines are reportedly due to multiple factors. Poor nutrition, which may be a result of current migratory pollination practices, is one such factor. Migratory pollination is a common practice of beekeepers from the Pacific Northwest and involves the placement of managed honey bee colonies within a series of cropping systems. There is a gap in knowledge on how migratory pollination practices impact honey bee nutrition. To understand the potential impacts of migratory pollination on honey bee nutrition, it is critical to assess the diversity of pollen collected by bees when colonies are placed adjacent to these cropping systems.
In this study, we describe the diversity of pollen collected by honey bee colonies managed by beekeepers in the Pacific Northwest region of the United States when placed in seven major cropping systems. We quantified the percent of target crop pollen and overall diversity of pollen collected by honey bees when colonies were placed in these cropping systems. We collected and identified pollen in almond (Prunus dulcis (Mill.)), cherry (Prunus avium L.), highbush blueberry (Vaccinium corymbosum L.), meadowfoam (Limnanthes alba Benth.), white clover (Trifolium repens L.), radish (Raphanus sativus L.), and carrot (Daucus carota (Hoffm.)) cropping systems. We found
that pollen collected from colonies placed in almond cropping systems was predominately Prunus sp., and hence, low in pollen diversity. At the other end of the spectrum, pollen collected from colonies placed adjacent to blueberry cropping systems did not yield any target pollen types (Highbush blueberry, Vaccinium corymbosum L.), but was high in overall pollen diversity. The pollen collected from colonies placed in other cropping systems was largely intermediate in diversity between these two extremes. There were not many plant species in bloom when pollen was collected from colonies placed in almond cropping system, whereas more plants were in bloom when we collected pollen from colonies placed in blueberry cropping system. The results of this study demonstrate that honey bees collected pollen from plants in the surrounding environment and collected different degrees of pollen diversity across different cropping systems in which the colonies were placed.
We further determined if pollen diversity influences colony-level protein utilization and biosynthesis of protein in nurse bees by conducting a pollen feeding experiment. Pollen collected from four different cropping systems in the first study was used to formulate four different diets, each varying in pollen diversity. We measured protein consumption in experimental colonies and by sampling nurse bees from each colony to estimate hypopharyngeal gland protein content and proteolytic enzyme activity after five weeks of feeding on the experimental pollen diets. Experimental colonies fed on pollen collected from almond cropping system exhibited a high protein consumption rate. However, low protein content as found in hypopharyngeal glands of nurse bees in these colonies. The nurse bees in these colonies also had low proteolytic enzyme activity, which indicates a lower rate of protein digestion. Overall, these results suggest that the diet representing pollen collected from almond cropping systems had low digestion rate and may have resulted in lower nurse bee hypopharyngeal gland protein. However, we cannot say this with certainty, as there were other confounding factors involved, such as presence of pesticides in the pollen collected from the cropping systems.