Beans Get a Bee Buzz

By Edith Munro, Contributing Editor

There’s a new buzz in the soybean field. Scientists now say natural pollinators like bees may also be important for self-pollinating crops, such as soybeans.

When colony collapse disorder began devastating bee populations in 2006, scientists started taking a closer look at all bees and pollination in general. While the honeybee has a reputation as a hard worker, it was native bees that turned out to be dominating pollination in a number of studies, says Steve Hendricks, a University of Iowa biologist.

“We found that most of the pollination at the produce farms we studied is by wild bees, even when honeybees are present,” Hendricks reports. “That has also been found in California watermelons and in studies in New Jersey. They are very effective pollinators.”

Increase soybean yield? At Iowa State University, entomologists are looking at how pollinators might affect soybeans—even though the crop has always been considered self-sufficient.

“If you had asked me a few years ago about the numbers of bees in soybean fields, I would have said very few,” says Matt O’Neal, ISU entomologist.

Then, O’Neal’s laboratory tried a different trapping system and captured close to 2,000 pollinators in central Iowa soybean fields over two years. Only four honeybees showed up in the sample that included some 30 species of pollinators.

“Some of the bees had soybean pollen on them,” O’Neal says, noting that studies in Michigan found a similar result in fields of corn. “I can’t emphasize how surprised I was. Most of what we’re finding is ground-nesting bees, green metallic bees and syrphid flies.

“We don’t know how much benefit the soybean plant gets, but this suggests that these beneficial insects may be helping us,” he adds.

ISU scientists are taking a closer look at how bees may affect bean yields by using a pollination-dependent soybean variety. They’ll be comparing fields with a large pollinator population versus fields with relatively few bees.

There is already some evidence bees can boost yields when they work soybean plants. A short-term Canadian study found the presence of bees was associated with much higher yields in food-grade soybeans. Australian research found increases of 10 to 40% in honeybee-pollinated soybeans compared to naturally self-pollinated plants.

A Brazilian project in 2005 looked at soybean seed production in cages with and without honeybee colonies. The cages with bees yielded 50% more seed soybeans.

“We clearly haven’t optimized their help,” O’Neal says of native bees. “Maybe by doing just a little bit more like offering them some habitat, we might be able to increase their impact.”

Habitat hints. Bee researchers are working to confirm that habitat along roadsides, field edges or on idled ground improves native bee numbers, and more work is ongoing to identify the most beneficial mix of plants for different regions. In Corn Belt states, recommended plants often include traditional prairie plants, such as bee balm, asters, wild indigo, prairie clover and purple coneflower.

For farmers interested in promoting native pollinators, a growing body of information is available from USDA’s Natural Resources Conservation Service (NRCS) and from web sites like the Native Pollinators in Agriculture Project (www.agpollinators.org), The Xerces Society for Invertebrate Conservation (www.xerces.org/pollinator) or USDA (www.nrcs.usda.gov/wps/portal/nrcs/site/national/home).

Encouraging native pollinators can mean higher payments per acre for new Conservation Reserve Program (CRP) contracts, and habitat projects may be eligible for Environmental Quality Incentives Program (EQIP) matching funds. For details on CRP and EQIP bee-related options, contact your local NRCS office. �

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