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Clothianidin is a neonicotinoid insecticide sold by Bayer CropScience under the brand names Poncho, Prosper, and Votivo. Clothianidin and other neonicotinoids are suspected as the cause of Colony Collapse Disorder (CCD), a phenomenon in which entire colonies of bees mysteriously and rapidly die off.[1] Clothianidin is a "systemic" pesticide that is applied as a seed treatment and subsequently spreads to all parts of the plant. It was first used in the U.S. on corn and canola in 2003. In December 2010, following a leaked EPA memo, pesticide watchdog groups and beekeepers called on the EPA to issue "an immediate stop-use order on the pesticide while the science is redone, and redesigned in partnership with practicing beekeepers."[2] The half-life of clothianidin ranges from 148 to 1,155 days (roughly from just under 5 months to over 3 years).[3]

Clothianidin and Honeybees

Clothianidin is one of two neonicotinoids that is used on almost all corn planted in the United States (the other is thiamethoxam, which turns into clothianidin when honeybees metabolize it).[3] This is significant as corn is the "single largest use of arable land in North America."[3] It takes only 22 to 44 nanograms (billionths of a gram) to kill 50% of honeybees exposed. However, when administered to the bees orally, a mere 2.8 to 3.7 nanograms is sufficient to kill 50% of honeybees. One kernel of corn can contain enough clothianidin to kill 80,000 honeybees. While corn does not rely on honeybees for pollination (it uses wind), corn pollen is a significant food source for honeybees.

The Krupke Study

A study published in 2012 analyzed clothianidin and thiamethoxam in soils, pollen (both collected by honey bees and directly from plants), dandelion flowers, dead and healthy bees, and waste products produced during the planting of treated seed, defined below:

"Sowing of maize seed in North America is accomplished using tractor-drawn planters that employ a forced air/vacuum system and a perforated disc to pick up individual seeds and drop them into the planting furrow at the selected spacing. Because maize kernels are treated with neonicotinoids and other compounds (usually fungicides) they do not flow readily and may stick to one another, causing uneven plant spacing. To remedy this, talc (a common mineral composed of hydrated magnesium silicate) is typically added to seed boxes to reduce friction and stickiness and ensure smooth flow of seed during planting. Much of the talc is exhausted during planting, either down with the seed or behind the planter and into the air using an exhaust fan."[3]

The study found that "clothianidin was found on all the dead and dying bees we sampled, while the apparently healthy bees we sampled from the same locations did not contain detectable levels of clothianidin." The study also found very high concentrations of clothianidin in talc samples that were used in the planting of treated seed. Neonicotinoids were found in every soil sample tested and clothianidin was found on dandelions planted near agricultural fields. Clothianidin was found in half of the samples of pollen taken from fields and also in samples of pollen collected by bees. No clothianidin was found in nectar.[3]

The study found:

"These results demonstrate that honey bees living and foraging near agricultural fields are exposed to neonicotinoids and other pesticides through multiple mechanisms throughout the spring and summer. The potential for greatest exposure (and the period when mortality was noted), occurs during planting time when there is potential for exposure to extremely high concentrations of neonicotinoids in waste talc that is exhausted to the environment during and after planting. Furthermore, we show that bees living in these environments will forage for maize pollen and transport pollen containing neonicotinoids to the hive. Pollen contaminated with levels of neonicotinoids similar to those shown in our results has been known to impair pollinator health."[3]
"After sampling anthers directly and identifying maize pollen in our samples, we know that pollen originating from treated seed does contain clothianidin, although not at the levels found in some of the bee-collected pollen samples, indicating the likelihood of additional pathways or sources. The levels of clothianidin in bee-collected pollen that we found are approximately 10-fold higher than reported from experiments conducted in canola grown from clothianidin-treated seed."[3]

The study concluded that clothianidin is present on the surface of soil in a field long after seed treated with clothianidin is planted. Perhaps more significantly, it found:

"Of potentially greater concern are the very high levels of neonicotinoids (and fungicides) found in the talc that has been exposed to treated seed, since part of this highly mobile material is exhausted to the outside environment during planting and after planting. The large areas being planted with neonicotinoid treated seeds, combined with the high persistence of these materials and the mobility of disturbed soil and talc dust, carry potential for effects over an area that may exceed the boundaries of the production fields themselves. A key mechanism for honey bee exposure may occur during the period when maize is typically planted across much of the Midwest (mid- April through early May). At this time, the energetic requirements of honey bee colonies are increasing rapidly and pollen and nectar resources are being gathered for colony growth. Talc and soil dusts from planting are mobile and have the potential to contaminate any flowering plants that are commonly found in or near agricultural fields and are visited by honey bees, including dandelion (Taraxacum officinale), which has been shown to be a preferred pollen and nectar source for honey bees during this period, when floral resources are relatively limited."[3]

When corn pollen is present, bees use it as a food source, often consuming pollen contaminated with clothianidin. The study found that if a nurse bee is eating pollen with an average amount of clothianidin (based on the study findings), it would consume 50% of the LD50 (the dose that would be lethal to 50% of bees) of clothianidin each day. "Lethal levels of insecticides in pollen are an obvious concern, but sublethal levels are also worthy of study as even slight behavioral effects may impact how affected bees carry out important tasks such as brood rearing, orientation and communication."

Clothianidin Scandal Timeline

In the U.S., the EPA does not allow a pesticide on the market until it is registered. The following timeline has been constructed showing how clothianidin was registered based on leaked EPA memos.

  • February 2003: A leaked EPA memo from February 2003 shows that EPA scientists initially called for "a complete worker bee life cycle study (about 63 days) . . . as well as an evaluation of exposure to the queen" prior to allowing Clothianidin on the market, as they worried it "has the potential for toxic risk to honey bees."[4]
  • April 2003: A second leaked memo reiterates concern about clothianidin's toxicity to bees, but now agrees to conditional registration, with the requirement of a "chronic life cycle study that evaluates the sublethal effects of clothianidin to the hive over time."[5] The conditional registration allowed the product on the market, but required the study in order to complete the registration. The study was to include "an evaluation of two complete life cycles (~130 days), including egg, larvae, adult stages, and mortality of the honey bee colony;" "an evaluation of the exposure and effects to the queen during these life cycles;" "provide clothianidin residue analysis of the stored nectar, honey, and pollen at the beginning of the study, at periodic intervals during the study and at the end of the study;" and "the study must include replicated data with statistical comparison to controls." Following the study, the EPA planned to asses whether a strong warning label on the product would be required. They recommended the following text for the label: "This compound is toxic to honey bees. The persistence of the residues and the expression of clothianidin in nectar and pollen suggests the possibility of chronic toxic risk to honey bee larvae and the eventual stability of the hive."
  • May 2003: Clothianidin is given a conditional registration for use as a seed treatment on corn and canola, with the study to be performed by December 2004.
  • March 2004: A third leaked memo shows that Bayer requested and was granted an extension until May 2005 to complete their study and permission to make changes to the study. Before, they were to perform the study in the U.S., but now they were given permission to do the study in Canada on canola.[6] Canola is a minor crop in the U.S., compared to corn. Corn is a major source of pollen for honey bees.
  • August 2006: Bayer completes and turns in its study, over one year after the May 2005 deadline.[7]
  • November 2007: The EPA reviews the study and deems it "acceptable." Clothianidin's registration for seed treatments on corn and cotton is completed.[8]
  • 2008: Natural Resources Defense Council sues the EPA over their failure to provide the study in response to a FOIA request. Also, beekeeper Tom Theobald finds the missing study on the internet, along with the several EPA memos about the registration of clothianidin.[9]
  • July 2010: Theobald writes an article about the memos and the study for Bee Culture.[10] He says, of the EPA's assessment that Bayer's study is scientifically sound: "Scientifically sound? If you’re in 4th grade perhaps, but certainly not if you have a Phd after your name. They should be embarrassed, this makes a mockery of science."
  • November 2010: In a memo to the management the EPA's Environmental Fate and Effects Division, Joseph DeCant (an EPA ecologist) and Michael Barrett (an EPA chemist) assess whether to register clothianidin for seed treatments for both mustard and cotton.[11] They say: "Clothianidin’s major risk concern is to nontarget insects (that is, honey bees). Clothianidin is a neonicotinoid insecticide that is both persistent and systemic. Acute toxicity studies to honey bees show that clothianidin is highly toxic on both a contact and an oral basis." They also note the previous study, saying: "A previous field study (MRID 46907801/46907802) investigated the effects of clothianidin on whole hive parameters and was classified as acceptable. However, after another review of this field study in light of additional information, deficiencies were identified that render the study supplemental. It does not satisfy the guideline 850.3040, and another field study is needed to evaluate the effects of clothianidin on bees through contaminated pollen and nectar. Exposure through contaminated pollen and nectar and potential toxic effects therefore remain an uncertainty for pollinators."
  • December 2010: Theobald and Pesticide Action Network obtain the November memo and take the issue public. Pesticide Action Network and Beyond Pesticides issued a joint statement to the press, "calling for an immediate stop-use order on the pesticide while the science is redone, and redesigned in partnership with practicing beekeepers."[12]

Clothiandin Products

For Home Gardeners:

  • 12 Month Tree & Shrub Protect & Feed II: Made by Bayer. Contains Imidacloprid and Clothianidin. Registered for use on outdoor trees and shrubs and containerized plants but not plants grown for food. Used to kill Adelgids, Aphids, Borers, Caterpillars, Japanese Beetles, Leafminers, Scale, and Whiteflies.[22]

Articles and resources

Related SourceWatch articles


  1. EPA Hides Data on Pesticide Link to Bee Die-Off, Society of Environmental Journalists, September 10, 2008, Accessed December 8, 2010.
  2. Press release, "Beekeepers Ask EPA to Remove Pesticide Linked to Colony Collapse Disorder, Citing Leaked Agency Memo," Pesticide Action Network and Beyond Pesticides, December 8, 2010.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Krupke CH, Hunt GJ, Eitzer BD, Andino G, Given K (2012) Multiple Routes of Pesticide Exposure for Honey Bees Living Near Agricultural Fields. PLoS ONE 7(1): e29268. doi:10.1371/journal.pone.0029268
  4. Clothianidin Conditional Registration Timeline, Pesticide Action Network North America.
  5. Clothianidin Conditional Registration Timeline, Pesticide Action Network North America.
  6. Clothianidin Conditional Registration Timeline, Pesticide Action Network North America.
  7. Jill Richardson, Leaked Memo Sheds Light on Mysterious Bee Die-Offs and Who's to Blame, Alternet, December 10, 2010, Accessed December 15, 2010.
  8. Clothianidin Conditional Registration Timeline, Pesticide Action Network North America.
  9. Jill Richardson, Leaked Memo Sheds Light on Mysterious Bee Die-Offs and Who's to Blame, Alternet, December 10, 2010, Accessed December 15, 2010.
  10. Tom Theobald, Do We Have a Pesticide Blowout?, Bee Culture, July 1, 2010, Accessed December 15, 2010.
  11. Memo: Clothianidin Registration of Prosper T400 Seed Treatment on Mustard Seed (Oilseed and Condiment) and Poncho/Votivo Seed Treatment on Cotton, U.S. EPA, November 2, 2010.
  12. Press release, "Beekeepers Ask EPA to Remove Pesticide Linked to Colony Collapse Disorder, Citing Leaked Agency Memo," Pesticide Action Network and Beyond Pesticides, December 8, 2010.
  13. Poncho 600 label
  14. Poncho, Bayer, Accessed May 7, 2013.
  15. Poncho Beta label
  16. Poncho Beta, Accessed Marhc 7, 2013.
  17. Poncho VOTIVO.
  18. Crops, Accessed March 7, 2013.
  19. Overview, Accessed March 7, 2013.
  20. Prosper FX MSDS.
  21. Crops, Accessed March 7, 2013.
  22. 12 Month Tree & Shrub Protect & Feed II Label.

External resources

External articles