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|
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|
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 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|
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.