Bee diversity increases blueberry yields

Honey bee declines from ominous forces like Colony Collapse Disorder are taking their toll. Across the U.S., beekeepers reported a 31.1 percent loss of colonies during the 2012 to 2013 winter — an especially startling statistic when you consider how bees pollinate the majority of the world’s crops. A new study reveals how, for blueberries at least, it’s not the number of bees that count, but the number of species. Blueberry plants produce more seeds and larger fruits when a diversity of bees visits their flowers.

To study the contribution of bees to crop productivity, a North Carolina State University team led by Shelley Rogers surveyed the bee community and measured pollination on three commercial blueberry farms in North Carolina. Using transects and little traps made of plastic soufflé cups, they observed 2,177 bees from five different families forage on highbush blueberry plants (Vaccinium corymbosum) during bloom season in two years.

And the researchers didn’t just look at openly pollinated flowers. To sample fruits resulting from individual bee visits, the team meticulously placed No-see-um mesh cages on branches with unopened flowers, and then removed them during bloom season. They observed the virgin flowers for visits by managed honey bees, Apis mellifera, and from a wild specialist, the southeastern blueberry bee (Habropoda laboriosa). To make sure no other bees visited the flowers, they caged the blossoms up right after. They collected the resulting fruits 50 days later and dissected them to count the seeds.

The team found that the abundance of domesticated Apis and the number of different species of wild bees are both equally important in pollination. With wild bees, however, species richness was a better predictor of pollination than abundance. They also found that various bees responded differently to weather: Apis bees were three times less abundant in inclement weather (when it’s overcast, with high winds, and 19 degrees Celsius or lower), while wild bumblebees, carpenter bees, and small native bees carried on rain or shine. Different bees coming at different times stabilizes the number of flower visits (and the resulting pollination) over time.

Farmers should enjoy more stability and productivity with diverse pollinator communities. The team even calculated an exact number: For each additional species present during bloom, fruits produced an average of 3.66 more viable seeds. This translates to $757 per hectare, or $1.4 million for all highbush blueberry grown in North Carolina each year. We know that bees provide ecosystem services; now it looks like their diversity offers biological insurance. — Janet Fang | 15 May 2014

Source: Rogers, S.R., Tarpy, D.R. & Burrack, H.J. Bee Species Diversity Enhances Productivity and Stability in a Perennial Crop, PLoS ONE (2014). doi:10.1371/journal.pone.0097307

Image: Hannah Burrack via NCSU