Study Claims Colony Collapse Disorder Caused By Insecticides

Jon Sullivan

A new study claims to have pegged neonicotinoids as the definitive cause of Colony Collapse Disorder. But does the data really justify the conclusions?

European honey bees are incredibly important pollinators. Unfortunately, they're disappearing at a rapid rate due to a phenomenon known as colony collapse disorder (CCD). What actually causes CCD isn't completely understood. CCD has confused scientists since it was first described, or had its name changed, in 2006. It is likely caused by a number of different factors, working together -  however, there has been a large focus on a certain group of insecticides known as neonicotinoids. In December of 2013, in an attempt to mitigate their involvement, the EU implemented a two-year memorandum on three commonly used insecticides in the neonicotinoid family. Many, including their own government, criticized the science behind the moratorium

There is a desperate need for new studies to accurately test the different variables involved in CCD. New research from Dr. Alex Lu attempts to peg neonicotinoid insecticides as the underlying cause of CCD. The study set up 18 hives to test the effects of two neonicotinoids, clothianidin and imidacloprid, from 2012-2013. Six colonies were selected from three different sites in central Massachusetts, and sublethal doses of each insecticide were given orally to treatment hives via a syrup solution. Six of twelve treated colonies abandoned their hives while only one of the six control hives abandoned theirs. Neonicotinoids obviously do not help bees, but whether this study has found them to be the ‘smoking gun’ isn’t exactly as clear as many are making it out to be. Only 18 hives were used in this study which is too small of a sample size to control for other variables and definitely too small to form a definitive conclusion as to the affects of neonicotinoids. The way he tests for CCD-like symptoms is not a definitive indication that is occurring. Hive abandonment is not automatically CCD. Honey bees may abandon their hives for any number of different reasons, and this study doesn’t control for any of them. 

Interested parties should be cautioned against making snap decisions and read Dr. Lu’s studies critically. One of his previous studies, which implied similar results, was also criticized for making comprehensive generalizations based off of a small sample size and administering inappropriate concentrations not commonly found in the field. Studies that make claims like this, if credible, should be in journals with a much higher impact-factor with more critical peer-reviewers. 

According to the USPA

“Until there are sufficient data to establish plausible adverse outcome pathways with consistent and reproducible linkages between molecular initiating events and key events across multiple levels of biological organization to an adverse effect at the whole organism/colony/population level, it is difficult to make use of sublethal effects other than in qualitatively describing potential adverse effects.”

In other words, there needs to be measurable biological responses to sublethal effects of neonicotinoids and they need to be able to get the same results again and again. Dr. Lu's study does not do this. 

It’s tempting to blame pesticides for any number of different things. They are formulated to kill things, and “chemical” has become a major buzzword, but the dose really does make the poison. Neonicotinoids may interfere with navigation; but are the doses force-fed to bees an accurate representation of when bees naturally forage and why does this matter? Imagine you are at a bar and have one shot of bourbon and then try to find your car. You’ll probably be fine. What if you had 10, 20, or even 50? You're probably not going to make it very far. It’s the same concept with insecticides, and it’s hard to accurately administer realistic doses in the lab and especially in the field. Using field studies where bees were able to naturally forage, researchers have not found reliable, direct evidence neonicotinoid treated plants are the primary underlying cause of CCD-like symptoms in honey bees. This of course doesn't rule out that they may be a contributing factor. In science, as in life, things are complicated. It's rarely as simple as 1 cause = 1 effect. Multiple factors are involved.

Another major problem with laying the blame of CCD solely at the feet of neonicotinoids is the fact Australia uses these insecticides, and they have yet to report a single case of CCD. The immediate noticeable difference in Australian hives is they remain free of the incredibly destructive Varroa mites. In the United States, managed hives dropped in number with the introduction of Vorroa mites in 1987 but are now actually increasing, even if overwintering hive losses have gone up.

So what is the cause of CCD? The long and short of it is the scientific community consisting of hundreds of entomologists, toxicologists, bee biologists and bee keepers don’t think it’s any one thing but a combination of multiple different variables. 

Possible but not limited to major causes of CCD:

Varroa destructor mites

Nosema apis and Nosema ceranae fungi

Bee nutrition and forage loss



Poor bee husbandry and moving bees

There are plenty of reasons for concern. Both pollinators and insecticides are integral in the safety and advancement of agriculture. Pollinators should be monitored and looked after carefully, and insecticides should be applied according to their label. There is a need for unbiased studies to monitor and observe the effects we have on beneficial insects, and there is a need for better research than Dr. Lu’s to make definitive judgments that may end up altering policy. 

Free review articles for additional reading:


Jake Bova is a graduate student at Virginia Tech. You can find him at his Facebook page, Relax, I'm an entomologist.

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