CAS number  YesY
ChemSpider  YesY
Jmol-3D images Image 1
Molecular formula C8H10ClN5O3S
Molar mass 291.71 g mol−1
Density 1.57 g/cm3
Melting point 139.1 °C (282.4 °F; 412.3 K)
Solubility in water 4.1 g/L
R-phrases R22
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N   YesY/N?)

Thiamethoxam is a systemic insecticide in the class of neonicotinoids. It has a broad spectrum of activity against many types of insects.


  • History 1
  • Mechanisms of action 2
  • Toxicity 3
  • Regulation 4
    • USA 4.1
    • European Union ban in 2013 4.2
    • Other countries 4.3
  • References 5


Thiamethoxam was developed by Syngenta; a patent dispute arose with Bayer which already had patents covering other neonicotinoids including imidacloprid. In 2002 the dispute was settled, with Syngenta paying Bayer $120 million in exchange for worldwide rights to thiamethoxam.[3][4]

Mechanisms of action

Thiamethoxam is a broad-spectrum, systemic insecticide, which means it is absorbed quickly by plants and transported to all of its parts, including pollen, where it acts to deter insect feeding. An insect can absorb it in its stomach after feeding, or through direct contact, including through its tracheal system. The compound gets in the way of information transfer between nerve cells by interfering with nicotinic acetylcholine receptors in the central nervous system, and eventually paralyzes the muscles of the insects.[5]:17

Syngenta asserts that thiamethoxam improves plant vigor by triggering physiological reactions within the plant, which induce the expression of specific "functional proteins" involved in various stress defense mechanisms of the plant allowing it to better cope under tough growing conditions, such as "drought and heat stress leading to protein degradation, low pH, high soil salinity, free radicals from UV radiation, toxic levels of aluminum, wounding from pests, wind, hail, etc, virus attack".[6]:16


The selective toxicity of neonicotinoids like thiamethoxam for insects versus mammals is due to the higher sensitivity of insects' acetylcholine receptors.[7]

The in vitro and in vivo toxicology tests.[5]:20

FAO described thiamethoxam as non-toxic to fish, daphnia and algae, mildly toxic for birds, highly toxic to midges and acutely toxic for bees.[5]:20 The Globally Harmonized System of Classification and Labelling of Chemicals (GHS) classification is: "Harmful if swallowed. Very toxic to aquatic life with long lasting effects".[5]:20



Thiamethoxam is approved for use in the US as an antimicrobial pesticide wood preservative and as a pesticide; it was first approved in 1999.[8]:4 & 14 As of 2014, it is approved for use in a wide range of crops.[9]

On September 5, 2014 Syngenta petitioned the EPA to increase the legal tolerance for thiamethoxam residue in numerous crops.[10] It wants to use thiamethoxam as a leaf spray, rather than just a seed treatment, to treat late to midseason insect pests.[11]

European Union ban in 2013

In 2012, several peer reviewed independent studies were published showing that several neonicotinoids had previously undetected routes of exposure affecting bees including through dust, pollen, and nectar; that sub-nanogram toxicity resulted in failure to return to the hive without immediate lethality, the primary symptom of colony collapse disorder; and showing environmental persistence in agricultural irrigation channels and soil. However, not all studies have found significant effects, and the studies carried out to date have not reached a clear conclusion on the impacts of neonicotinoids.[12] These reports prompted a formal peer review by the European Food Safety Authority, which stated in January 2013 that neonicotinoids pose an unacceptably high risk to bees, and that the industry-sponsored science upon which regulatory agencies' claims of safety have relied on may be flawed and contain several data gaps not previously considered.[13] In April 2013, the European Union voted for a two-year restriction on neonicotinoid insecticides. The ban restricts the use of imidacloprid, clothianidin, and thiamethoxam on crops that attract bees.[14]

Other countries

Thiamethoxam is approved for a wide range of agricultural, viticultural(vineyard), and horticultural uses.[5]:17


  1. ^ Thiamethoxam at Sigma-Aldrich
  2. ^ MSDS for Thiamethoxam
  3. ^ Syngenta AG has reached an agreement to pay Bayer AG $120 million to settle a dispute over neonicotinoid chemistry used in insecticides, February 1, 2002
  4. ^ Bayer (11 January 2002). "Syngenta and Bayer reach agreement on patent disputes". Retrieved 15 April 2012. 
  5. ^ a b c d e "FAO Specifications and Evaluations for Agricultural Pesticides: Thiamethoxam". 21 June 2000. 
  6. ^ Syngenta (2006). "Thiamethoxam Vigor Effect" (PDF). Retrieved 2011-10-11. 
  7. ^ Patrick H Rose (2012). "6.3.2.Selective Toxicity of Nicotine and Neonicotinoids,". In Marrs, Timothy C. Mammalian Toxicology of Insecticides. The Royal Society of Chemistry. p. 186.  
  8. ^ EPA Dec 21, 2011 Thiamethoxam Summary Document Registration Review Initial Docket Entire docket is available here
  9. ^ §180.565 Thiamethoxam; tolerances for residues.
  10. ^ Environmental Protection Agency (EPA) (5 September 2014). "Receipt of Several Pesticide Petitions Filed for Residues of Pesticide Chemicals in or on Various Commodities". Federal Register 79 (172): 53009–530013. Retrieved 13 September 2014. 
  11. ^ Britt E. Erickson (15 September 2014). "Syngenta Stands Firm On Neonicotinoids". Chemical & Engineering News (American Chemical Society) 92 (37): 7. Retrieved 13 September 2014. 
  12. ^ "Scientific opinions differ on bee pesticide ban". Retrieved 22 November 2013. 
  13. ^ European Food Safety Authority (2012) "Assessment of the scientific information from the Italian project 'APENET' investigating effects on honeybees of coated maize seeds with some neonicotinoids and fipronil" EFSA Journal 10(6):2792
  14. ^ "Bees & Pesticides: Commission goes ahead with plan to better protect bees". Retrieved 22 November 2013.