Clothianidin: Dangerous Compared to What?

I recently spent some time in the comments on a Mother Jones post that was ostensibly about how a Bayer-produced pesticide is causing Colony Collapse Disorder (mysterious disintegration of bee colonies) and seed companies are conspiring to force pesticide seed coating on farmers.

Some of the commenters were pretty challenging and I learned quite a bit about a particular neonicotinoid pesticide clothianidin. Like most pesticides it is actually pretty dangerous — and is increasingly looking particularly dangerous to bees — but like everything else in agriculture we have to ask how it’s being used and what it’s replacing.

Update on 7/09 09:45: Please also see a newer post that considers whether clothianidin is really worth the cost.

Clothianidin Exposure Routes

One commenter linked me to an article1 specifically about how clothianidin could be affecting bees more than previously expected due to unexpected exposure pathways. This was actually the first article I’ve read2 that was actually measuring real environmental exposures to a neonicitinoid pesticide. There have been several3 4 5 high profile studies recently that showed unexpectedly large harmful effects on bees. Two of these, however, are using estimated exposure rates based on other studies which seem somewhat problematic to me6 (the third is behind a paywall but does look like it might be actual measured exposure). They are still useful results — if a particular bee species gets this sub-lethal amount of a pesticide, then they have trouble with normal bee tasks. But a critical piece is exactly how much they are actually getting from agricultural use. All pesticides are going to have an effect on some animal, and often ones we don’t intend, so the goal is to find ways to minimize that exposure.

This study actually describes how a pesticide — added as a seed-coating so that it will continue to work against pests as the plant grows — may be exposing bees to more of the pesticide than expected. This is extremely interesting to me because a major advantage of seed-coating is that it reduces environmental exposure. Relatively small amounts coat the seed and they are translocated throughout the plant as it grows, ideally only affecting pests that eat the plant itself. The seeds studied here are corn (maize) which is wind-pollinated and it wasn’t expected that bees ate all that much of the pollen. What they found was first that bees were eating a lot more corn pollen than expected. Since the seeds were treated with clothianidin, the pollen had some clothianidin, specifically 3.9 parts per billion so the bees were consuming a fair bit of poison7.

Later in the season, when planting is largely complete, we found that honey bees will collect maize pollen that contains translocated neonicotinoids and other pesticides from seed. Translocation of neonicotinoids into pollen has previously been reported for maize grown from imidacloprid-treated seed [26], although the degree to which honey bees in our study gathered maize pollen was surprising.

More interesting to me is that the pesticide-coated seeds have to be coated in talc before planting to keep from jamming the equipment. The residue talc and dust was contaminated with pesticide (anywhere from around 3000 to 15000 parts per million) which they postulate could be falling on other flowers that bees forage on which the authors see as a significant risk of exposure.

Both soil and dandelion flowers obtained from the fields closest to the affected apiary (soybeans in 2010, unplanted when sampled in 2011) contained clothianidin (Table 6), therefore clothianidin in/on the dandelions could have resulted from translocation from the soil to the flower, from surface contamination of the flowers from dust, or a combination of these two mechanisms. Dandelion flowers growing far from agricultural areas served as controls; no neonicotinoids were detected.

Ban it! Ban it!

You might think from reading this that we should ban this pesticide immediately. But that seems premature to me. First, the authors themselves note that better handling of talc and dust residues could remove 99% of the risk from that exposure route.

A recently published review of the risks posed by planting treated seeds in the E.U. estimates that measures taken there may reduce the dust generated during planting by 99% [33]. In North America, different planting equipment is used and there are currently no guidelines for disposal of waste talc, nor are there devices for filtering exhaust material from the vacuum planting systems. Producers may be largely unaware that this material is highly toxic to pollinators. However, given the unprecedented levels of maize production across the United States, coupled with the increasing adoption of neonicotinoid seed treatments in other annual crops covering a wide area, including soybeans (31.3 million ha), wheat (24.7 million ha), and cotton (4.4 million ha, all figures 2010 planting) [9], it is clear that this material presents a risk that is worthy of further investigation and possibly corrective action.

Considering the talc measurements were the highest concentrations they found (all other measurements of pesticide concentration in pollen, nectar, soil, adjacent flowering plants, and bees themselves were below 15 parts per billion compared to more than 10,000 parts per million for the talc), this seems the most critical aspect to mitigate. The concentrations in maize pollen are much smaller though the authors note that the bees are eating a surprising amount of corn pollen:

Maize pollen was frequently collected by foraging honey bees while it was available: maize pollen comprised over 50% of the pollen collected by bees, by volume, in 10 of 20 samples.

So it’s pretty clear this pesticide is harmful to bees though (whether it’s strongly relatd to CCD or not is pretty unclear and this paper does not describe CCD effects). Clothianidin was definitely known to be harmful to bees when it was conditionally registered, though these methods of exposure were not. Do these exposure routes mean it should be banned?

Neonicotinoid pesticides only became common in the 1990s (clothianidin was only given conditional registration in the US in 2003). The alternatives are organophosphate, carbamate and pyrethroid pesticides (these are of course still used as well for many different uses). The neonicotinoids appears to be less toxic to a large numbers of animals, including mammals, which gives another reason to use them (a major risk of working in agriculture is significant and harmful pesticide exposure). Pyrethroids are extremely toxic to many aquatic organisms at very small concentrations. Organophosphate insecticides are extremely harmful to insects and humans. Both organophosphates and pyrethroids will kill bees merely on contact: unlike clothianidin the bees do not have to eat them to be harmed. Clothianidin was initially approved (partially) because it has lower risk to mammals and birds. Coating seeds with it is yet another way to reduce the harmfulness of what is applied (since there is far less of it) and because it’s less likely to run-off into waterways.

We haven’t as a society banned every other pesticide and yet many of the others still used are extremely harmful: to bees, to insects, to aquatic animals, and so on. Modern agriculture is very dependent on pesticides to maintain good yields with little damage to the crops. If corn seeds aren’t coated with this pesticide, then farmers will attempt to control the pests in other ways. This might involve spraying throughout the season, with greater amounts of pesticide and likely with more broadly harmful ones.

Another Way?

I see the last few decades of agricultural science as a period of finding ways to decrease harm while still producing truly staggering amounts of food. One of the ways we’re doing that is by creating plants that can fight off their own pests better. If you’ve never heard of “Bt corn” or the phrase “Cry1Ab protein” before, I recommend this primer.

So right now we only have plants that can fight off only a few organisms. The pesticides (proteins) generated by the plant are fairly specific but limited. They don’t harm humans when eaten or the environment with runoffs. Unlike seed-coating, there’s no contaminated dust or talc to contaminate other plants. We need more of these. But if you don’t like the idea of killing pest insects, researchers are finding ways to just “scare off” pests. But the common element of both these general techniques is that we apply less pesticides that affect broad swaths of animals, pests or not. If we increasingly target our pest control only against pests affecting our crops, then we’re less likely to affect other organisms.

We need to fix the known problems with clothianidin. But I can’t say from this evidence that we should stop using it entirely. The EPA has communicated what evidence they need to see to take it off the market. It reiterates that clothianidin is far less harmful than alternatives it replaces, both to bees and humans. But clothianidin isn’t really the point. The point is that we’re still mostly using broad-spectrum chemical pesticides when we should be targeting pest controls much more narrowly. Genetic engineering, as with Bt corn, is a technology we should be expanding.



  1: Krupke, C., Hunt, G. et. al. 2012. Multiple Routes of Pesticide Exposure for Honey Bees Living Near Agricultural Fields. PLoS ONE 7(1): e29268. doi:10.1371/journal.pone.0029268.


Since I’m not a scientist, don’t fully keep up with the literature and haven’t done a full literature search, this is pretty unsurprising. I was just glad someone in a thread actually pointed out something relevant! Actually measuring environmental exposure and contamination is a pretty critical piece of the puzzle.


Tapparo A, Marton D, et. al. 2012. Assessment of the environmental exposure of honeybees to particulate matter containing neonicotinoid insecticides coming from corn coated seeds. Environ Sci Technol. 2012 Mar 6;46(5):2592-9.


Henry M, Béguin M, et. al. 2012. A Common Pesticide Decreases Foraging Success and Survival in Honey Bees. Science. 2012 Apr 20;336(6079):348-50


Whitehorn P, O’Connor S, et. al. 2012. Neonicotinoid Pesticide Reduces Bumble Bee Colony Growth and Queen Production Science. 2012 Apr 20;336(6079):351-2


Whitehord P, et. al. chose 6 µg/kg of imidacloprid for pollen for their low end and 0.6 µg/kg for nectar based on Quantification of Imidacloprid Uptake in Maize Crops. J. Agric. Food Chem., 2005, 53 (13), pp 5336–5341. Unfortunately I can’t read it all, but the abstract mentions an average of 2.1 µg/kg in pollen and doesn’t mention nectar at all. I do wish Science would allow a little less brevity. Henry M, et. al. chose 1.34 ng thiamethoxam in 20 µl of sucrose solution but doesn’t, as far as I can tell, indicate how this was chosen or if anyone has estimated actual environmental exposure to this pesticide. These are still interesting results, of course, but perhaps say less about the real world than media reports gave them credit.


I suspect this is because I’m not good at this, but I can’t figure how many samples were collected to form this statistic.