Seed insecticides hurt honeybees

Honeybee populations have been in serious decline for years, and Purdue University scientists may have identified one of the factors that cause bee death around agricultural fields.

Analyses of bees found dead in and around hives from several apiaries over two years in Indiana showed the presence of neonicotinoid insecticides, commonly used to coat corn and soybean seeds. These insecticides were present at high concentrations in waste talc exhausted from farm machinery during planting.

The insecticides clothianidin and thiamethoxam were also consistently found at low levels in soil up to two years after treated seed was planted, and on nearby dandelion flowers and in corn pollen gathered by bees.

Key Points

Neonicotinoid insecticides are fatal to honeybees.

Nearly all corn seed, and about half of all soybean seed, is coated with insecticides.

Entomologists call for limiting or ending talc emission from planting operations.


“We know that these insecticides are highly toxic to bees; we found them in each sample of dead and dying bees,” says Extension entomologist Christian Krupke.

Greg Hunt, a Purdue professor of behavior genetics, says no one factor is to blame for declining bee numbers, though mites and insecticides are all working against bees.

Talc factor

The insecticide coatings are sticky. In order to keep them flowing freely in the vacuum system used in many planters, they are mixed with talc. Excess talc is released during planting and routine planter-cleaning procedures.

“Given the rates of corn planting and talc usage, we are blowing large amounts of contaminated talc into the environment,” Krupke says. “The dust is quite light and appears to be quite mobile.”

Krupke says corn pollen that bees were bringing back to hives later in the year tested positive for neonicotinoids at levels roughly below 100 parts per billion.

“That’s enough to kill bees if sufficient amounts are consumed, but it’s not acutely toxic,” he says. On the other hand, exhausted talc showed extremely high levels of insecticide — up to about 700,000 times the lethal dose for a bee.

“Whatever was on the seed was being exhausted into the environment,” he says. “This material is so concentrated that even small amounts landing on flowering plants around a field can kill foragers, or be transported to the hive in contaminated pollen. This might be why we found these insecticides in pollen that the bees had collected and brought back to their hives.”

Action needed

Krupke suggests efforts be made to limit or eliminate talc emissions during planting.

“That’s the first target for corrective action,” he says. “It stands out as being an enormous source of potential contamination, not just for honeybees, but for insects living in or near those fields.

“The fact that these compounds can persist for months or years means that plants growing in these soils can take up these compounds in leaf tissue or pollen,” he concludes.

Wallheiner writes for the Purdue University Ag Communications department.

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Contaminated talc: Entomologists suspect that talc contaminated with insecticide released into the environment at planting adds to honeybee deaths. Scrape out boxes instead of blowing them out, they suggest.

This article published in the March, 2012 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.