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Where Bees Get Their Pollen and Pesticides

Urban gardeners and mosquito-abatement could be partly to blame for bee declines.

By Nathan Collins


(Photo: Philippe Huguen/AFP/Getty Images)

The decline in bee populations spells bad news for agriculture and, in turn, our food supply. Scientists strongly suspect that agricultural pesticides are playing a role in that decline, but, according to a new study, that isn’t the whole story: In some places, bees get most of their pollen from uncultivated plants like clover, and they pick up a diverse assemblage of pesticides in the process.

What’s happening with bees is complicated to say the least. As with many disappearing species, declining habitat and biodiversity is partly to blame. So are diseases and parasites. Of late, however, a class of insecticides called neonicotinoids have been getting the most attention, and not without reason: They’re ubiquitous in corn and wheat, stick around for a long time, and are generally pretty bad for bees.

The question is, what other pesticides might bees be picking up, and where are they picking them up in the first place?

Farmers aren’t the only ones to blame for bee declines.

To find out, Ohio State University entomologist Elizabeth Long and Purdue University entomologist Christian Krupke split six beehives between three separate sites in Indiana. Two of the beehives were placed in an open meadow with wildflowers, trees, and shrubs; another two at the edge of corn field planted with neonicotinoid- and fungicide-treated seeds; and two more at the edge of a corn field planted with untreated seeds. For 16 weeks in 2011, Long and Krupke gathered pollen from their bee colonies. After first classifying the pollen, they then analyzed it for its pesticides.

Honeybees, Long and Krupke found, did not feast primarily on pollen from cultivated plants, but rather from the Fabaceae plant family, which includes clover, alfalfa, and soybeans. Even bees living next to treated corn fields got about one-third of their pollen from clover and only about one-fifth from corn.

And the pesticides? “Surprisingly, although the pesticides used in agricultural production were consistently present as contaminants of honeybee-collected pollen, they were not the contaminants present in highest concentrations,” the researchers report. Neonicotinoids were fairly common, but the most commonly detected were fungicides and herbicides.

Of greatest concern, however, may be another group of insecticides called pyrethroids, which appear to affect bees’ ability to move and interact with one another. “Although a variety of agricultural pesticides were found at all sites, the contaminants likely to provide the greatest hazard to honeybees in our study were non-agricultural pyrethroid insecticides targeting nuisance pests such as mosquitoes,” Long and Krupke write.

In other words, farmers aren’t the only ones to blame for bee declines. “Our work demonstrates that the pest-management practices employed both within crop fields and beyond have implications for honeybee and other pollinator populations in the area,” Long and Krupke add, “as both urban and agricultural pesticides were relatively common in all types of pollen throughout the season.”