When it comes to producing oilseed, the more honeybees and other pollinators that visit a flowering field of Brassica carinata, the better.

This is one of the insights South Dakota State University researchers gained about the relationship between honeybees and native pollinators — such as bumblebees, butterflies, moths, wasps and flies — and Brassica carinata, a member of the mustard family. The oil extracted from carinata seeds can be refined into jet fuel or biodiesel.

“We found that yield is very positively affected by pollinators, and the more pollinator visitation we see, the higher the yield of the plants,” says Charles B. Fenster, who led the study. Fenster is a faculty member in the Department of Biology and Microbiology in the College of Natural Sciences and a researcher and interim assistant director for the South Dakota Agricultural Experiment Station.

The researchers assessed carinata seed production and pollinators at 36 1-acre plots within a 30-mile radius of Brookings. Cages prevented pollinators from accessing a specific number of plants in each plot. In addition, honeybee hives were added to half the sites.

The researchers identified 28 different species that carry pollen from carinata, according to postdoctoral researcher Henning Nottebrock, who previously worked on plant-pollinator dynamics in South Africa. In addition, he says, pollinators that travel among different plants bring higher quality pollen and increase seed set.

To relate pollinator visits to seed set, the researchers observed each of five 1-square-meter sites within a plot for 20 minutes, counting the pollinators and noting if the insects gathered nectar from flowers within the same plant or different plants. 

“We looked at focal plants and counted visits and later harvested the plants, counting the number of seeds per fruit and the number of viable seeds produced,” Nottebrock explains. The seed was viable if it had an endosperm.

“A high number of pollinator visitations can double the carinata seed set,” he says. These results are in agreement with other researchers’ findings on pollinators in canola, which showed a 46% seed increase.

“When we exclude the pollinators, it significantly lowers seed yield,” he says.

The researchers also looked at the effect of landscape diversity. They identified the different crops, bodies of water, marginal land and forest within approximately a 2-mile radius of each carinata plot.

“We generally found the greater the landscape diversity around the plots, the higher the seed yield and the higher the insect visitation,” Fenster says.

Neonic effects
At half the study sites, carinata seeds were treated with different types of neonictinoids before planting.

“These seed treatments modified plant-pollinator interactions, depending on the scale,” Noteboom says. “When carinata is treated with neonics, the pollinators do not like it.”

Other studies suggest that some of the chemical goes into the nectar and pollen.

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