Seed treatments linked to bee deaths

Photo provided by Purdue University's Department of Entomology

By Matt Reese

Bees are big business, pollinating $15 billion in crops per year including apples, cherries and berries.

The dollar figures involved are generating significant concern as pollinator populations continue to decline worldwide. More people are demanding answers about the factors behind the colony collapse disorder blamed for bee deaths.

“We saw a 3% loss in hives per year from 2007 to 2012 in the U.S.,” said Christian Krupke, associate professor of entomology at Purdue University. “More and more of the arrows are pointing to pesticides in a more convincing way as a part of colony collapse disorder.”

Mites, weather and other factors are certainly involved in the decline in bee populations, but Krupke has found fairly conclusive evidence that the use of neonicotinoid insecticides in seed treatments for corn and soybeans is at least partially to blame in areas of production of those crops. Analyses of bees found dead in and around hives from several apiaries over two years in Indiana showed the presence of neonicotinoid insecticides.

“We do know that bees living near fields where treated seeds are planted have multiple routes of exposure to neonicotinoid through the spring and summer. Poncho dominates the annual crop market and a single Poncho-treated corn kernel has enough active ingredient to kill a couple hundred thousand honeybees,” Krupke said. “Analysis of dead bees in Indiana coincided with corn planting in the area. And, analysis of the dead bees revealed traces of neonicotinoid insecticides. Also, stored pollen from hives with dead bees outside had various levels of pesticides. This was lower in healthy hives. Nurse bees that stay in hive and don’t leave also had traces of pesticides.”

In contrast, though, the Ohio Department of Agriculture received dead bee reports in six counties in 2012, but no pesticides were found in any of the bee samples. All of the Ohio cases did occur near the time of corn planting, however.

Photo provided by Purdue University's Department of Entomology.

The next question, though, is how do the bees come into contact with pesticides in seed treatments. Krupke’s research showed that the insecticides from seed treatments were present at high concentrations in the waste talc that is exhausted from farm machinery during planting. The waste talc serves as vector to just about anywhere the wind will carry it, including dandelions, purple dead nettle and other plants at the field edge that are popular with bees.

“Whatever goes on the seed comes out in the talc in very high concentrations,” Krupke said. “Any honeybee that flies through that planter exhaust is not going back to the hive. That, of course, is not all that common.”

With this this in mind, Krupke and other researchers will be looking at how mobile the waste talc really is and at ways to reduce the problem.

“Industry was initially not receptive, but they have now decided to work with researchers to develop new methods of lubricating seed to avoid the use of talc,” Krupke said. “Farmers did everything right in each case of bee deaths we found, this is not the case of applicator error.”

It also brings up the question, is such widespread use of insecticides in seed treatments really necessary? In some cases, the insecticides have important yield benefits, but there is not much evidence that supports the current level of use, Krupke said.

“The benefits for yield and pest control are not clear. In our research, we did not see any significant differences in corn yields with seed treatments, though we did find positive trends in yield. Does this mean that seed treatments don’t work? No, that is not what it means. But it does mean we do not necessarily need these in every situation. I don’t think we see much benefit in treating every single seed in every single year,” Krupke said. “We have been using pesticides for a long time and we know that pesticides and bees can coexist.”

In addition to the insecticide, the fungicides in seed treatments are also harmful to bees.

“Fungicides do not acutely kill bees, but they are not great for them either,” Krupke said. “We need to quantify these things through more research.”

In the mean time, when planting time arrives, farmers can improve the situation by simply being aware of the problem and minimizing the chances for waste talc to drift. This includes proper planter cleaning and maintenance.

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One comment

  1. The biggest advance in this study is the acceptance of the word ‘drift’. No one was allowed to use that word, even when visual inspection clearly indicated it was the culprit. Perhaps we should consider that it is improper for colleges, etc. that accept huge amounts of largesse from seed and pesticide companies to be the persons to investigate claims.

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