This was a big week for bee news!  New research on bees and pesticides was published, and a major white paper from the Xerces Society on the same topic was released.

The pesticides in question are called Neonicotinoids, since they are derived from nicotine (used as a pesticide since the 1700’s). “Neonics” are systemic insecticides, or insecticides that are taken up by a plant’s tissues and circulate within the plant. This makes these pesticides a highly effective and relatively safe insect control method, since only insects that eat the plant will be affected. It also is sometimes the only way to kill insects inside a plant; an insect boring into a tree, for example, can’t be sprayed directly.

Neonicotinoid pesticides can also be applied as a root drench or a seed treatment, so there is no pesticide sprayed into the air, or landing where it should not go.  Farmers love neonicotinoids, since they not only reduce “off-target” effects, they last a really long time–usually one application can last for months, and sometimes over a year.  That saves a lot of money.

The problem is…because the insecticide circulates in plants’ tissue, it shows up in flower nectar and pollen. And that’s what bees collect and concentrate, and take back and feed to their young.  What initially seemed to be a very environmentally-friendly group of insecticides is turning out to be a risk for bees.

Carl Zimmer’s excellent New York Times summary of the research on bees and pesticides is a must read:  Bees’ decline linked to pesticides.

“In Thursday’s issue of the journal Science, two teams of researchers published studies suggesting that low levels of a common pesticide can have significant effects on bee colonies. One experiment, conducted by French researchers, indicates that the chemicals fog honeybee brains, making it harder for them to find their way home. The other study, by scientists in Britain, suggests that they keep bumblebees from supplying their hives with enough food to produce new queens….The authors of both studies contend that their results raise serious questions about the use of the pesticides, known as neonicotinoids.”

Carl (I shook his hand once, so I can call him Carl, right?) does a great job of showing how the scientific community is still resolving how all this research adds up.  In a post on his blog providing supplimental information to the NYTimes story above, Carl discusses the difficulty of making sense of all this information:

I found this story to be especially challenging to sum up in a single nut graph. To begin with, these experiments came after many years of previous experiments and surveys, which often provide conflicting pictures of what’s going on with insecticides and bees. The experiments themselves were not–could not–be perfect replicas of reality, and so I needed to talk to other scientists about how narrow that margin was. As they should, the scientists probed deep, pointing out flaws and ambiguity–in many cases even as they praised the research.
At the same time, these two papers 
did not appear in a vacuum. Other scientists have recently published studies (or have papers in review at other journals) that offer clues of their own to other factors that may be at work. And, biology being the godawful mess that it is, it seems that these factors work together, rather than in isolation.

If Carl Zimmer–an exceptional science journalist with access to the actual scientists that are doing the research–is having trouble trying to create a coherent picture of the information about these pesticides, I KNOW that the rest of us regular schmoes are struggling too.

Here is the important thing to remember as you process this new bee research:  CCD, or colony collapse disorder in honeybees, does not have a single cause.  It’s likely that many different factors work together to create CCD.  It is a complex set of specific symptoms, and it’s been known since around 1900 by many other names. Additionally, not all observed bee declines (and deaths) are CCD. It’s hard out there for a bee.

There is clearly a pesticide problem with bees–even if we can’t fully quantify it right now.  The Xerces Society white paper, A Review of Research into the Effects of Neonicotinoid Insecticides on Bees, with Recommendations for Action, had this to say about CCD:

“There is no direct link demonstrated between neonicotinoids and the honeybee bee syndrome known as Colony Collapse Disorder. However, recent research suggests that nenonicotinoids may make honey bees more susceptible to parasites and pathogens….which has been implicated as one causitive factor for CCD.”

The Xerces paper is probably the best review of the recent research that you are going to find.  Not only is it written by Xerces scientists, who are folks what really know their bees, it also was reviewed by several other bee researchers I have a great deal of respect for.

Data table from the Xerces report showing...lots of gaps

Xerces thoroughly documents what we know about these pesticides and bees–and, unfortunately, we don’t know nearly enough. Most of the published research focuses on honey bees, rather than the native bee species in the US.  (Honey bees are an introduced species in North America).  That means we don’t have much data to work with to figure out how different bee species will be affected.

Personally, I found the most disturbing piece of the Xerces report to be their discovery of how many of these neonicotinoid insecticides are available over the counter to homeowners.  Calculating pesticide application rates is one of the toughest parts of farming (or pesticide applicator exams), and Xerces does the math to uncover some startling facts:

  • “Products approved for homeowners to use in gardens, lawns, and on ornamental trees have manufacturer-recommended application rates up to 120 times higher than rates approved for agricultural crops. 
  • Many neonicotinoid pesticides that are sold to homeowners for use on lawns and gardens do not have any mention of the risks of these products to bees, and the label guidance for products used in agriculture is not always clear or consistent.
  • Neonicotinoids can persist in soil for months or years after a single application. Measurable amounts of residues were found in woody plants up to six years after application.”

That is really scary.

Xerces raises some very important questions about what this means for our native bees that are already struggling with habitat loss and a spill-over of parasites and pathogens from introduced bee species. Butterflies, beetles, and flies also drink nectar and feed on pollen–pretty much any of our pollinators, including hummingbirds, could be affected if they feed on trees and plants treated with these insecticides.

bee photoI hope that new labeling is introduced so consumers know that these products have the potential to kill bees and other pollinators.  Unfortunately, because these pesticides are so very useful in agriculture, there are no easy answers. The things that make these compounds so very well suited for so many purposes–their ability to remain stable for a long time and spread through plant tissues–are also why they pose dangers for pollinating insects.

Additional Reading: 

Posted by Gwen Pearson

Writer. Nerd. Insect Evangelist. Have you heard the good news? BUGS!


  1. So, neonicotinoids are working their way up the food chain: from plants to insects and from them to birds and all the wildlife that feeds on insects. It is Silent Spring all over again. Sigh.

  2. Yes @Bug_Girl that’s right!!!
    The two Science papers address only one of the gaps of knowledge rightly pointed by Xerces, namely “What is the full extent of the sublethal effects of neonicotinoids on foraging, reproduction, and other behaviors of adult bees?”. Actually the papers do not even explore “the full extent” but only some of these effects, so far not studied as extensively as they now can be. The papers do not address the other gaps of knowledge on neonic effects that Xerces lists, and do also not address the other gaps of knowledge on bee decline (CCD or other). Indeed, in both papers the exposure step is very simplified and standardized in order to better focus on two difficult-to-detect, yet possibly significant at the colony level, effects on honey bee behavior and bumble bee reproduction. Therefore the authors of the papers (and I can better speak for the French ones here) do not claim that neonics are THE cause of bee decline, as journalists sometimes report too quickly (of course, conversely they also do not claim that neonicotinoids are some sort of vitamin for bees! insecticides kill insects…).
    The French study is part of a more ambitious program involving researchers (in ecology, genomics, toxicology etc.), beekeepers and agronomists to also look at diseases, habitat loss related to cropping systems, etc., taken separately or in combination, and in lab or field conditions. For instance last week INRA co-authored a paper in Nature Scientific Reports on the synergistic effects of another neonicotinoid and Nosema infection (
    Yet, in the view of last week’s results, the French government has already stated that it would reassess the risk of these chemicals and even, altogether, implement the risk assessment processes in relation to effects on bees.

  3. Thanks for this post, you have obviously done a lot of research. I find it especially sad that the general public feels the need to use pesticides in their gardens.

  4. It will be interesting to see how this plays out, but I’m sure those who care little for the science will grab it and run with it. It was good to see the Zimmer report had a picture of a honey bee and a thoughtful analysis (especially pointing out the problem with the honey bee study reliance on models) with attempts to seek a variety of views, but less objective reports will undoubtedly dominate (with bumble bee pictures, natch), e.g.:
    I suppose bees do collect corn pollen, but it is hard to see how that would help them get lost.

    The Goulson study is a worry, but the levels of insecticide used were extremely high and the results do not explain why some bumble bee species are declining and others not. Still, there are unintended consequences for most of our innovations and the way we tend to spread new miracle chemicals everywhere without much thought is a unfortunate character trait.

  5. James Salsman April 1, 2012 at 2:54 pm

    The Xerces Society review says, “There is no direct link demonstrated between neonicotinoids and the honey bee syndrome known as Colony Collapse Disorder.” The Schneider et al (2012) RFID study they cited and the more recent Henry et al RFID study published in Science last week both showed failure to return to the hive at low nanogram sublethal levels for two neonicotinoids. Failing to return to the hive is a unique signature of CCD, different than any other contemporary threat to bees, whether parasites, viruses, or other cumulative insecticides.

    What more would be necessary to demonstrate such a link?

  6. James–there are a specific set of criteria that must be met beyond just failing to return to the hive.

    Collapsed colonies
    1) complete absence of adult bees in colonies, with few or no dead bees in or around colonies,
    2) the presence of capped brood, and
    3) the presence of food stores (both honey and bee bread) that are not robbed by other bees or typical colony pests (small hive beetles, wax moths, etc.). If robbed, the robbing is delayed by a number of days.

    Collapsing colonies
    1) an insufficient number of bees to maintain the amount of brood in the colony,
    2) the workforce is composed largely of younger adult bees,
    3) the queen is present, and
    4) the cluster is reluctant to consume food provided to them by the beekeeper.

    Just having bees go away is not enough for a CCD diagnosis. Also, in the larger literature, neonicotinoids have a very inconsistent record–sometimes have an effect, sometimes not; sometimes not present in failed hives. That suggests a role, but not a causal one, for CCD.

  7. The single biggest trouble for the neonicotinoid/CCD connection is the lack of correlation in space between intensity of pesticide use and incidence of CCD. Here in Illinois, for instance, we’re drowning in pesticides but we don’t have reports of CCD.

  8. Exactly! There ought to at least be some sort of correlation–but there isn’t. It occurs with and without neonics. Which makes me think that Xerces has it right–it isn’t a primary cause, but can act as a synergist to make things worse.

  9. Midnight Rambler April 2, 2012 at 3:00 am

    Also, failure to return to the hive is not at all unique to either CCD or neonicotinoids. A presentation at the Entomological Society of America meeting last fall showed strong evidence that several common fungicides cause CCD-like symptoms (due to both the fungicides themselves and the “inactive ingredients” included in the formulations). Unlike most insecticides, these have often been sprayed without much regard to the presence of bees (after all, they’re not supposed to kill insects).

    But again, these are not likely to be the sole cause of CCD either. They’re used on things like apples, but many other crops don’t use them at all. Most likely, they’re one more synergist.

  10. Since I am getting this question a lot–what DOES cause CCD? There is a list of suspects; the first two on this list are usually found in hives with CCD:

    o–increased losses due to the invasive varroa mite (a pest of honeybees);
    o–diseases such as Israeli Acute Paralysis virus and the gut parasite Nosema;
    o–pesticide poisoning through exposure to pesticides for in-hive insect or mite control
    o–bee management stress;
    o–foraging habitat modification;
    o–inadequate forage/poor nutrition;
    o–potential immune-suppressing stress on bees caused by one or a combination of factors identified above; (including neonicotinoid pesticides)
    o–poor nutrition, drought, and migratory stress brought about by the increased need to move bee colonies long distances to provide pollination services.

  11. Thanx a lot! I am glad I could contribute a little color to your great scientific work. Keep it up.

  12. […] be thought of as ‘bee medical literature’–that early studies often do not pan out, especially when the underlying biology is multifactorial and complex. The other problem is that, based on the entomologists that I follow, the field really hasn’t […]

  13. […] Bug Girl, my favourite blogger on the subject of insects, turned up a telling piece of research that found insecticides approved for home use often have recommended application rates that are many hundred times higher than those recommended to farmers for agricultural use. (And that’s the recommended rate—how many people mix and apply the insecticides correctly?) […]

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