Are Seed Coatings Killing Bees?

I subscribe to a number of lists about topics I am interested in, and recently saw some stuff about a class of chemicals that have recently been banned in the EU, and is still in use here in the United States.

Seed coatings are nothing new—they have been around for years.  Mom used to plant her garden every year, and the sweet corn she planted had a red powder coating.  I don’t know what that was, but it was probably an insecticide of some kind.

If you watch TV in Iowa you have probably seen ads for something called “Poncho VOTiVO”.  That is a product that can be used as a seed treatment for corn, soybeans, sorghum, and sugar beets.  It consists of a bacteria that kills nematodes (a nearly microscopic type of round worm) and a chemical called clothianidin, which is a systemic insecticide and belongs to the class of chemicals called neonicotinoides which have recently been banned by the EU.

So the first newsletter article I looked at was from the University of Arkansas.  It included a video from Dr. Gus Lorenz, taking about some tests conducted by his lab. They found corn pollen which had as high as 2.3 parts per billion clothianidin, and found none in soybean flowers and cotton nectar.  He said that these chemicals really are not showing up in any great amounts in areas where bees could be hurt. The article says that neonicotinoides are “barely found” in the pollen of seed-treated plants.

He does have a slide where the detection levels of these chemicals in the soil “pre-treatment” are shown.  The class of chemicals showed up in levels of greater than 1 part per billion in the majority of the crop fields—98% of the cotton fields.  So those detections represent residue from previous crops.


The problem is that this chemical, and the neonicotinoid class of chemicals in general, is extremely toxic to bees.  The LD50 for ingestion (the amount of the chemical that kills 50% of bees that ingest it within 48 hours) is 4 nanograms/bee.  If you take the average weight of a bee to be 100 milligrams, that means that 40 ppb kills bees by ingestion.  That is 40 parts of the chemical per billion parts of bees.  There is also an LD50 for contact that is about 10 times higher.  Simply contacting 440 nanograms of the chemical will kill 50% of the average worker honeybees.


So the doses Dr. Lorenz found were sub lethal, but close enough that there should be concern.  I found a report on a Purdue study  to be more credible.  They sampled pollen, nectar, and dead bees from apiaries and found high levels.  They also found detectable levels of clothiandin in fields that had not been planted with treated seeds for two years.  They sampled dandelions from around field edges and found detectable levels of neonicotinoids.  They found it in planter exhaust.

I think this is a bigger issue than “just” the loss of bees.


About the roused bear

Nature photographer from central Iowa.
This entry was posted in insects, Uncategorized and tagged , , , , . Bookmark the permalink.

2 Responses to Are Seed Coatings Killing Bees?

  1. theresagreen says:

    That is a beautiful photograph of the bee. It is incredible that ‘experts’ condone the use of chemicals that contain any element of risk of harm to pollinators. It makes you wonder if they ever actually step outside and see the natural world at all doesn’t it?

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