Neonicotinoid

Neonicotinoids are a class of insecticides which act on the central nervous system of insects with lower toxicity to mammals. Neonicotinoids are among the most widely used insecticides worldwide, but recently the uses of some members of this class have been restricted in some countries due to a possible connection to honey-bee colony collapse disorder, though no scientific evidence has been established confirming that connection.

Mode of action

The neonicotinoids are a class of insecticides with a common mode of action that affects the central nervous system of insects, causing paralysis and death. Under the WHO / EPA classification these compounds are placed toxicity class II or class III. Because the neonicotinoids block a specific neural pathway that is more abundant in insects than warm-blooded animals, these insecticides are selectively more toxic to insects than mammals. They bind at a specific site, the postsynaptic nicotinic acetylcholine receptor, and there are no records of cross-resistance to the carbamate, organophosphate, or synthetic pyrethroid insecticides, thus making them important for management of insecticide resistance. As a group they are effective against sucking insects such as aphids, but also chewing insects such as Coleoptera and some Lepidoptera.

All of the neonicotinoids were registered after 1984 and were not subject to reregistration. Some uncertainties have been identified since their initial registration regarding the potential environmental fate and effects of neonicotinoid pesticides, particularly as they relate to pollinators. Some of the compounds within this class have been demonstrated to persist for several years and residues have been detected in plants for several years following application. Studies conducted in Europe in the late 1990s have suggested that neonicotinic residues can accumulate in pollen and nectar of treated plants and represent a potential risk to pollinators. Adverse effects on pollinators (beekill incidents) have also been reported in Europe that have further heightened concerns regarding the potential direct and/or indirect role that neonicotinic pesticides may have in pollinator declines, though no evidence of a link to such incidences has been established. Recently submitted registrant data from studies conducted in Europe have supported concerns regarding the persistence of neonicotinoids; however, the translocation of residues into pollen and nectar of treated plants and the potential effect that these residues may have on bees remains uncertain.^[1]

According to the United States Environmental Protection Agency registration review docket for imidacloprid opened in December 2008, and the docket for nithiazine opened in March 2009. To better ensure a “level playing field” for the neonicotinoid class as a whole, and to best take advantage of new research as it becomes available, the EPA has moved the docket openings for the remaining neonicotinoids on the registration review schedule (acetamiprid, clothianidin, dinotefuran, thiacloprid and thiamethoxam) to 2012.^[1]

Use

Imidacloprid is possibly the most widely used insecticide, both within the mode of action group and in the worldwide market. It is now applied against soil, seed, timber and animal pests as well as foliar treatments for crops including: cereals, cotton, grain, legumes, potatoes,^[2] pome fruits, rice, turf and vegetables. It is systemic with particular efficacy against sucking insects and has a long residual activity. The application rates for neonicotinoid insecticides are much lower than older, traditionally used insecticides.

Thiamethoxam (TMX) is a second generation neonicotinoid insecticide, belonging to the thianicotinyl subclass. Thiamethoxam's chemical structure is slightly different from other neonicotinoid insecticides, making it highly water soluble and therefore readily translocated in plant tissue. TMX is systemic and penetrates into the plant cells where it also triggers various physiological reactions,^[3] 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;
• Low pH;
• High soil salinity;
• Free radicals from UV radiation;
• Heat stress leading to protein degradation;
• Toxic levels of aluminum;
• Wounding from pests, wind, hail, etc., and;
• Virus attack.

In 2001, the US Patent and Trademark Office ruled in favor of Syngenta when the company filed suit against Bayer to protect its patent on a class of neonicotinoid insecticides.

Environmental impact

There is controversy over the role of neonicotinoids in relation to pesticide toxicity to bees and imidacloprid effects on bee population. Neonicotinoid use has been strictly limited in France since the 1990s, when neonicotinoids were implicated in a mass die-off of the bee population. It is believed by some to account for worker bees' neglecting to provide food for eggs and larvae, and for a breakdown of the bees' navigational abilities, possibly leading to what has become generally known as Colony Collapse Disorder.^[4][5]

It was banned in Slovenia in 2003 due to Colony Collapse Disorder. Its usage has later been allowed, but microbiology experts believe the decision was based on a quick and incomplete government research by the ministry and was influenced by Monsanto, an agricultural biotechnology company. Independent studies show that while the photodergradation half-life time of most neonicotinoids is around 34 days when exposed to sunlight, it might take up to 1386 days for these compounds to degrade in the absence of sunlight and microorganism activity. Some activists are concerned that neonicotinoids applied agriculturally might accumulate in aquifers.^[6]

In 2008 Germany revoked the registration of clothianidin for use on seed corn after an incident that resulted in the death of hundreds of nearby honey bees.^[7] Investigation of the incident revealed that it was caused by a combination of factors, among which were the failure to use a polymer seed coating known as a "sticker"; weather conditions that resulted in late planting when nearby canola crops were in bloom; a particular type of air-driven equipment used to sow the seeds which apparently blew clothianidin-laden dust off the seeds and into the air as the seeds were ejected from the machine into the ground; dry and windy conditions at the time of planting that blew the dust into the nearby canola fields where honey bees were foraging.^[8]; and a higher application rate which had been authorized for a severe root worm infestation. Clothianidin was also restricted for a short period for use on rapeseed; however, after evidence had shown that the problems resulting from maize seed were not transferable to rapeseed, its use was reinstated under the condition that the pesticide be fixed to the rapeseed grains by means of an additional sticker, so that abrasion dusts would not be released into the air.^{[9] [10]}

In 2009 the German Federal Office of Consumer Protection and Food Safety decided to continue to suspend authorization for the use of clothianidin on corn because it has not yet been fully clarified to what extent and in what manner had bees come into contact with the active substances in the pesticides belonging to the neonicotinoid group (clothianidin, thiamethoxam and imidacloprid) when used on corn. In addition, on the basis of new findings, the question arose as to whether drops of liquid from plants which are taken in by bees pose an additional risk.^[11]

Neonicotinoid seed treatment uses are banned in Italy, but foliar uses are allowed. This action was taken based on preliminary monitoring studies showing that bee losses were correlated with the application of seeds treated with these compounds; Italy also based its decision on the known acute toxicity of these compounds to pollinators.^[12][13]

Sunflower and corn seed treatments of the active ingredient imidacloprid are suspended in France; other imidacloprid seed treatments, such as for sugar beets and cereals, are allowed, as are foliar uses.^[12]

The 2009 documentary Vanishing of the Bees suggests that a link between neonicotinoid pesticides and colony collapse disorder exists, although the experts interviewed indicated that analysis of the data does not confirm such a linkage.^[14]

On July 23, 2010, Dutch toxicologist, Dr Henk Tennekes had a scientific paper published in the journal, Toxicology (online) titled,Druckrey-Küpfmüller equation for risk assessment.^[15] He then authored and published a book in regards to his research called "A Disaster in the Making". The book explores the impact of neonicotinoids on the immune system of bees.

Active substances

Available neonicotinoid insecticides include:

• Acetamiprid
• Clothianidin
• Dinotefuran
• Imidacloprid
• Nitenpyram
• Thiacloprid
• Thiamethoxam

References

1. ^ ^{a b} "Basic Information | Pesticides | US EPA". Epa.gov. http://www.epa.gov/oppsrrd1/registration_review/highlights.htm. Retrieved 2011-10-11. 
2. ^ Potato insecticides by group and mode of action (PDF)
3. ^ "Thiamethoxam Vigor Effect (Syngenta)" (PDF). http://www.syngenta-us.com/media/emedia_kits/thiamethoxamvigorus/media/pdf/presentation.pdf. Retrieved 2011-10-11. 
4. ^ Copping, Jasper (April 1, 2007). "Flowers and fruit crops facing disaster as disease kills off bees". The Telegraph. http://www.telegraph.co.uk/news/uknews/1547243/Flowers-and-fruit-crops-facing-disaster-as-disease-kills-off-bees.html. 
5. ^ Mysterious Bee Deaths Linked to Pesticides^{[dead link]}
6. ^ "Interview with microbiologist: "This place is filled with multinational lobbyists"". Delo.si. 2011-05-14. http://www.delo.si/brez%20kategorije/intervju-z-mikrobiologom-ta-prostor-je-prestreljen-z-lobisti-multinacionalk.html. Retrieved 2011-10-11. 
7. ^ Alison Benjamin. "Pesticides: Germany bans chemicals linked to honeybee devastation | Environment | guardian.co.uk". Guardian. http://www.guardian.co.uk/environment/2008/may/23/wildlife.endangeredspecies. Retrieved 2011-10-11. 
8. ^ "EPA Acts to Protect Bees | Pesticides | US EPA". Epa.gov. http://www.epa.gov/oppfead1/cb/csb_page/updates/2008/bees-act.htm. Retrieved 2011-10-11. 
9. ^ "Press releases and background information - Background information: Bee losses caused by insecticidal seed treatment in Germany in 2008". BVL. http://www.bvl.bund.de/EN/08_PresseInfothek_engl/01_Presse_und_Hintergrundinformationen/2008_07_15_hi_Bienensterben_en.html?nn=1414138. Retrieved 2011-10-11. 
10. ^ "Background information: Bee losses caused by insecticidal seed treatment in Germany in 2008". German Federal Office of Consumer Protection and Food Safety (BVL). 2008-07-15. http://www.bvl.bund.de/EN/08_PresseInfothek_engl/01_Presse_und_Hintergrundinformationen/2008_07_15_hi_Bienensterben_en.html?nn=1414138. 
11. ^ "Maize seed may now be treated with "Mesurol flüssig" again". German Federal Office of Consumer Protection and Food Safety (BVL). 2002-02-09. http://www.bvl.bund.de/EN/08_PresseInfothek_engl/01_Presse_und_Hintergrundinformationen/2009_02_09_pi_Maissaatgut_Mesurol_en.html?nn=1414138. 
12. ^ ^{a b} "Colony Collapse Disorder: European Bans on Neonicotinoid Pesticides | Pesticides | US EPA". Epa.gov. http://www.epa.gov/opp00001/about/intheworks/ccd-european-ban.html. Retrieved 2011-10-11. 
13. ^ Brandon Keim (Dec 13, 2010). "Leaked Memo Shows EPA Doubts About Bee-Killing Pesticide". Wired. http://www.wired.com/wiredscience/2010/12/epa-clothianidin-controversy/. 
14. ^ "2009 documentary ''Vanishing of the Bees''". Vanishingbees.co.uk. 2011-02-03. http://vanishingbees.co.uk/. Retrieved 2011-10-11. 
15. ^ Tennekes, Henk A. (2010). "The significance of the Druckrey–Küpfmüller equation for risk assessment—The toxicity of neonicotinoid insecticides to arthropods is reinforced by exposure time". Toxicology 276 (1): 1–4. doi:10.1016/j.tox.2010.07.005. PMID 20803795. http://boerenlandvogels.nl/sites/default/files/Tennekes_2010_Toxicology_9.pdf.