Beekeepers know that their hives are at risk when pesticides are sprayed anywhere nearby, and occasionally lose massive numbers of bees
to unanticipated spray programs. But the problem seemed to be manageable even in the 1950's and 1960's when large scale use of highly toxic pesticides was at its peak.
Colony collapse disorder is a syndrome - a cluster of symptoms - not actually a single disease, so far as we know. In the last decade many beekeepers have discovered that their colonies suddenly drop in numbers to the point of collapse. Sometimes the dying bees are found, as in this amateur blogger's
pictures. But it can be difficult to tell whether diseases, pesticides, or some other cause is responsible. What's clear is that there have been massive losses of honeybees for the last 10 years. This article
has a chart showing that losses more than doubled in most parts of Canada in the last 5 years. This summer I bought honey from a farmer near Creemore, Ontario who was so discouraged he was thinking of getting out of beekeeping. He had lost 85% of his colonies last winter.
In my last blog
I mentioned that a strange unintended consequence of large scale, industrial-level beekeeping may be serious harm to bumblebees. In this post, I want to talk about another unintended consequence of a well-intentioned change made by the pesticide industry about 20 years ago.
|Nicotiana alata by Carl E. Lewis - CC 2.0|
" pesticides were created 20-30 years ago to reduce harms to birds and mammals from pesticides. The name means new-nicotine-like and is descriptive. Tobacco plants make nicotine not for your smoking pleasure but because it is toxic to insects. In fact 100 years ago tobacco extracts were sprayed on greenhouse plants as a natural pesticide.
Nicotine, and the neo-nicotinoid pesticides, bind to an important receptor in nerves. Insect nerves are more disrupted by this than nerves of mammals or birds, making these compounds fairly safe for you, your cat, or your budgie. As such they were a great advance over the older generations of pesticides.
We humans are rarely content with just some improvement; we want more and more. So the chemists modified neonicotinoids to be persistent
(so a low dose would work longer) and soluble
in water. This meant an even smaller amount could be applied as a coating on seeds and soaked up by the sprouting seedling. This meant no spraying, and even protection of all parts of the plant. As a result neo-nicotinoid pesticides are now the most popular and widely used commercial pest control substance, with billions of $$$ in sales each year.
|treated corn seed|
As a result, corn growers now find it almost impossible to buy commercial quantities of high-yielding corn varieties that are untreated. Almost all seed (99.8%) sold is treated with a combination of a fungicide and a neonicotinoid.
That's why the findings of a team
led by Christian Krupke of Purdue University are so important. Prof. Krupke was called in when local beekeepers reported large bee die-offs around corn seeding time. Dead bees collected had measurable amounts of neonicotinoids. To determine if these could be a cause of death and how they might be getting into the bees, Krupke's team planted corn over two years using treated seeds and normal planting methods, as well as saved seed from the previous year (which was untreated).
Some of their results have been published online in the the journal PLoS One (available to anyone - click the link
). They discovered that a lubricant used to keep the coated seeds from sticking to each other - talcum powder! - ended up highly contaminated with pesticides. The contaminated talc is blown away and ends up coating spring flowers and plants near the fields. This is the first way bees are exposed.
|guttation drops, not dew|
The second exposure comes when the corn seedlings are just up. Many plants exude small droplets of sap from leaf tips at night when the humidity is high, called "guttation drops". To you or me they look just like dew, but bees know that they are sweet and will collect them just like nectar first thing in the morning. It's been known for several years now that guttation drops from treated corn seeds are so toxic they kill bees in just hours
. The risk to bees is highest in the first week after emergence
The third point of exposure is one of the least expected. When corn "flowers", that is when the tassels mature, vast amounts of pollen is available. Beekeepers have observed for years that bees will avidly collect corn pollen. Krupke's team found that foragers bees from hives near fields of treated corn were bringing back large amounts of corn pollen with significant levels of neonicotinoids in it. This pollen goes to feed new larval bees and newly emerged nurse bees in the hive. Over the life of one young bee in the hive, she would consume an amount of pesticide equal to 1/2 of the lethal dose for bees. This might or might not be fatal, but Krupke et al's analysis of dead and dying bees found near their hives showed much higher levels of neonicotinoids than from healthy bees.
The fourth exposure method is not discussed much in their recent article. However in a talk I heard Krupke give at the North American Pollinator Protection Campaign (NAPPC) 2011 conference, he told us that his colleagues found significant amounts of neonicotinoids in soils that had not been exposed to treated seeds for 2 years. Some estimates suggest these compounds may have a half-life of 15 years or more in the soil. This means that in fields planted with treated seed for 3 years out of a typical 4 year crop rotation, the "steady-state" level of neonicotinoids in the soil could end up several times higher than what is put on in any year.
So there's bad news and there's good news. The bad news is that even when the corn is long gone, the same fields may be producing flowers contaminated with neonicotinoids. The good news is that some of the contamination can be removed by improving seeding techniques - control that talcum powder!
|dead honeybees - Clement Kent, CC 2.0|
As one person at the NAPPC conference pointed out, the simplest, least debatable step would be for the manufacturers of neonicotinoids to tweak their formulas so that the pesticides are less persistent. This would give them something new to patent and help protect the environment. We can only hope that Bayer, Monsanto, Syngenta, and Dow take this message to heart, before we have converted much of our agricultural landscape into a toxic mess that will last a generation.
Krupke, C.H., Hunt, G.J., Eitzer, B.D., Andino, G., and Given, K. (2012). Multiple Routes of Pesticide Exposure for Honey Bees Living Near Agricultural Fields. PLoS ONE 7, e29268.