Sticky Situation on Bees

Honeybees Bring Home Cocktail of Pesticides

Pam Smith , Crops Technology Editor
A new study shows honeybees collect most of their pollen from sources other than corn and soybeans, but pesticides remain issue. (DTN photo by Pamela Smith)

DECATUR, Ill. (DTN) -- Midwest honeybees have a smorgasbord of dining options, but corn and soybeans are not their first choice of entrees. Instead, pollinators make a beeline for clovers or find flowering weeds along roadsides and ornamental plants in urban settings more to their taste.

These findings from a recent Purdue University study point to a broader responsibility for the plight of pollinators. The problem is bees still pick up an amazing array of pesticides even if they skip over commercial crops, said Purdue University entomologist Christian Krupke.

Krupke and fellow researcher Elizabeth Long collected pollen from Indiana bee colonies over a 16-week span from May to September to discover what kinds of pesticides honeybees actually do collect as they forage. Hives were placed in a non-agricultural meadow, the border of a cornfield planted with neonicotinoid-treated seeds and the border of a cornfield planted with non-treated seeds. The scientists waited to begin their collections until after growers had planted their crops to avoid contaminated dust that can arise when farmers use air planters to plant pesticide-treated seeds.

Krupke told DTN the resourcefulness of the bees in finding such a wide range of plants to forage on, even close to agricultural fields, was the surprise in the findings. He said the diversity and abundance of pesticides found in each sampling session throughout the season was also remarkable. "There was no break [in exposure] and the patterns did not match up with agricultural practices, such as foliar sprays for in-season pest problems," Krupke said.

Krupke found the pollen collected during the study contained a similar diversity of pesticides regardless of where the hives were placed. Pyrethroids were the predominant insecticide bees brought home to the hive, but the presence of those pesticides spiked in late-summer months.

Krupke said pyrethroid use increases in those months to control wasps and hornets and late-summer mosquito populations. "The pyrethroids we found at the highest levels are not widely used in agriculture, and in fact they don't even have labels for use in field crops," Krupke said. Pollen from all three sites also contained very low levels of DEET, the active ingredient in most insect repellants.

In total, the pollen samples contained pollen from 30 plant families and residues from 32 different pesticides spanning nine chemical classes. Fungicides and herbicides were the most prominent pesticides isolated in the pollen samples. Neonicotinoid insecticides, long targeted as a culprit in pollinator problems, were found among the mix, despite the fact the study was delayed to avoid the dust-off issue.

"The sheer numbers of pesticides we found in pollen samples were astonishing," he said. "Agricultural chemicals are only part of the problem. Homeowners and urban landscapes are big contributors, even when hives are directly adjacent to crop fields."

In a press release, Krupke said the study suggests that overall levels of pesticide exposure for honeybees in the Corn Belt could be considerably higher than previously thought. The researchers did not measure concentration or lethal doses of the pesticides found in the pollen. The study represents one year of data, and colony health was not part of the assessment.

Few studies have examined how non-crop plants could expose bees to other classes of pesticides. Looking at Midwestern honeybees' environment through this wider lens and over an entire season could provide more accurate insights into what bees encounter as they forage, Krupke said.

He added that little is known about how these diverse pesticides interact with one another to affect bees. The toxicity of insecticides, for example, can increase when combined with certain fungicides, themselves harmless to insects.

The study also brings up new questions on current efforts to plant pollinator habitat. "It does seem a wide range of plants will pick up pesticides, either by the pesticide landing on the plant or by picking up water-soluble pesticides through the soil," Krupke said.

"We don't know enough to talk about what a 'safe zone' would be, or how to implement that. One of the take-home messages from the work is that things like pollinator gardens will always just nibble around the edges of the problem. Seeing where we can reduce pesticide use is the key approach and this work highlights targets for that," he said.

The study was published in Nature Communications and is available at…

Pamela Smith can be reached at

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Pam Smith