An Interesting Study of One Factor Causing Colony Collapse Disorder

The following is a summary of:

Pettis JS, Lichtenberg EM, Andree M, Stitzinger J, Rose R, et al. (2013) Crop Pollination Exposes Honey Bees to Pesticides Which Alters Their Susceptibility to the Gut Pathogen Nosema ceranae. PLoS ONE 8(7): e70182. doi:10.1371/journal.pone.0070182

A study published by the University of Maryland and the US Department of Agriculture in late July offers tantalizing evidence of the cause of Colony Collapse Disorder.

Researchers in the study gathered pollen from honey bee hives throughout the East Coast from Delaware to Maine. They analyzed the samples to determine if the pollen contained pesticides. They found that on average each sample contained 9 different agricultural chemicals. All pesticide levels were sublethal, and the two most common chemicals found were a fungicide, chlorothalonil, and an insecticide, fluvalinate, used by beekeepers to control Varroa mites.  Varroa mites are a common honeybee pest, and I will write another entry on them soon.

Researchers then fed health honeybees the contaminated pollen samples. They found that the honeybees lost their ability to fight off Nosema, a fungus that also affects honey bees, when they were fed the samples containing chlorthalonil. The results were surprising, and research Dennis vanEngelsdorp noted:

“We don’t think of fungicides as having a negative effect on bees, because they’re not designed to kill insects, Federal regulations restrict the use of insecticides while pollinating insects are foraging, he said, “but there are no such restrictions on fungicides, so you’ll often see fungicide applications going on while bees are foraging on the crop. This finding suggests that we have to reconsider that policy.”

The more I read on the topic, the more I am forced to conclude that there is not one smoking gun causing colony collapse disorder. I think there are probably a number of factors interacting to cause the colony collapses we have seen over the past decade.  And, while this study is not direct evidence on the cause of colony collapse disorder, it does offer an explanation for at least one of the factors that is causing stress on the honey bee populations.

See here for the original study published online.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0070182

All About Neonicotiniods

Neonicotiniods are the primary suspect in the investigation for the cause of Colony Collapse Disorder. The next several blog entries will discuss the investigation and the evidence. This blog entry will introduce neonicotiniods.

Neonicotinoiods were welcomed as a ground-breaking class of insectides when they were first marketed in 1991 by Bayer A.G. By 1995 they were the top selling insecticide in the world and generated $360B in annual sales.[i] The most common neonicotinoids in use are imidacloprid, clothianidin and thiamethoxam.

Neonicotinoids are acetylcholine agonists related chemically to nicotine. Acetylcholine is the most common neurotransmitter in the body and is found in both the central nervous system (CNS) and the peripheral nervous system (PNS). In the CNS, acetylcholine plays a major role in our sensory perceptions, making us more alert and sharpening our attention to details. In the PNS, acetylcholine plays a major role in muscle activation.[ii]  As an acetylcholine agonist, neonicotinoids block the site on neurons where acetylcholine will bind and prevent the neuron from firing. This will effectively stop neural transmissions, resulting in loss of focus, loss of muscular control, lethargy, and, ultimately, paralysis and death. What a great way to kill an insect!

Neonicotinoids are typically applied in what is called a seed treatment. Seeds are ‘dressed’ or coated in the insecticide prior to planting. The insecticide is then absorbed by the plant is it grows and develops, so the insecticide provides long lasting protection against pests. Seed treatments are generally considered more environmentally friendly since their precise application results in lower soil contamination from run-off and an overall lower amount of insecticide is applied to the environment.

The popularity of neonicotinoids can be attributed to three main reasons, as outlined by Randy Oliver on scientificbeekeeping.com:

1. They are far more toxic to insects than to mammals, making them much safer for humans.
2. They are absorbed by plants and translocated via the vascular system, giving effective control of sap sucking and boring insects which other sprayed insecticides might not contact.
3. They can be applied as seed treatments, thus being a solution to the longstanding problem that roughly 99% of sprayed treatments never actually hit a target pest, and thus are unnecessarily dumped into the environment.[iii]

In summary, when neonicotinoids were first introduced to the market in the 1990s, they were considered the important development in pesticide development over the prior 50 years due to lower environmental impact and lower toxicity to humans. They are currently the most commonly used pesticide on the market today.

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[i] Legocki, Jan, and Iwona Polec. “Contemporary trends in development of active substances possessing the pesticidal properties: neonicotinoid insecticides.” PESTYCYDY / PESTICIDES 1 (2008): 143-59. http://www.wydawnictwa.ipo.waw.pl/pestycydy/2008-1-2/Legocki.pdf. Institute of Industrial Organic Chemistry. 10 Feb. 2013.

 

[ii] Cherry, Kendra. “What Is Acetylcholine?” About.com Psychology. About.com. 10 Feb. 2013 <http://psychology.about.com/od/aindex/g/acetylcholine.htm&gt;.

 

[iii] Oliver, Randy. “ScientificBeekeeping.com.” Scientific Beekeeping RSS. Sept. 2012. ScientificBeekeeping. 10 Feb. 2013 <http://scientificbeekeeping.com/neonicotinoids-trying-to-make-sense-of-the-science-part-2/&gt;.

 

Killing Me Softly… Study in Science Journal Suggests Deadly Impact of Neonicotinoids

A study published in the journal Science and conducted by Mickael Henry of the French National Institute for Agricultural Research (INRA) in Avignon involved gluing microchips to the backs of honeybees so they could be tracked. Researchers then gave a portion of the bees a low dose of a neonicotinoid pesticide. Of course, some of the bees were not given any pesticide in order to serve as the control group. The activities of the two groups of bees were then tracked and compared. The results were not unexpected. The group that was treated with neonicotinoids were 2-3x more likely to die while away from the hive as compared to the control group. The scientists hypothesized that this was likely due to impairment of the honeybee’s navigational ability by the neonicotinoids. The bees were simply unable to find their way home and died.

A second study led by Dave Goulson of Stirling University in Scotland investigated the impact of neonicotinoids on a developing honeybee colony. Honeybee nests were weighed, including bees, wax, honey, grubs, and pollen, and then placed in an enclosed site that allowed bees to live under natural conditions for six weeks. Some of the hives were treated with low levels of neonicotinoids and others that served as the control group were not treated. After six weeks, the honeybee nests were weighed again. The group treated with neonicotinoids was 8-12% smaller than the control group and produced 85% fewer honeybee queens.

These findings are very significant, because most environment protection rules require application of pesticides at a level that is not toxic to bees. However, these studies show that even low, non-toxic levels might not immediately kill a bee but will still eventually lead to the death of a bee.

All information in this blog entry is from:

Kelland, Kate. “Studies Show How Pesticides Make Bees Lose Their Way.” Reuters. Thomson Reuters, 27 Mar. 2012. Web. 06 May 2013. <http://www.reuters.com/article/2012/03/29/science-pesticides-bees-idUSL6E8ET2JM20120329&gt;.