Imidacloprid

Use

Imidacloprid is one of the most widely used insecticides in the world. Its major uses include:

• Seed treatment – Imidacloprid is a popular seed treatment insecticide in the world
• Agriculture – Control of aphids, cane beetles, thrips, stink bugs, locusts, and a variety of other insects that damage crops
• Arboriculture – Control of the emerald ash borer, hemlock woolly adelgid, and other insects that attack trees (including hemlock, maple, oak, and birch)
• Home Protection – Control of termites, carpenter ants, cockroaches, and moisture-loving insects
• Domestic animals – Control of fleas (applied to the back of the neck)
• Turf – Control of Japanese beetle larvae (exp. Grubs)
• Gardening – Control of aphids and other pests

When used on plants, imidacloprid, which is systemic, is slowly taken up by plant roots and slowly translocated up the plant via xylem tissue.

Application to trees

When used on trees, it can take 30–60 days to reach the top (depending on the size and height) and enter the leaves in high enough quantities to be effective. Imidacloprid can be found in the trunk, the branches, the twigs, the leaves, the leaflets, and the seeds. Many trees are wind pollinated. But others such as fruit trees, linden, catalpa, and black locust trees are bee and wind pollinated and imidacloprid would likely be found in the flowers in small quantities. Higher doses must be used to control boring insects than other types.

Use in the United States

The estimated annual use of the compound in US agriculture is mapped by the US Geological Service and shows an increasing trend from its introduction in 1994 to 2014 when it reached 2000000 lb. However, use from 2015 to 2019 dropped following concerns about the effect of neonicotinoid chemicals on pollinating insects. In May 2019, the Environmental Protection Agency revoked approval for a number of products containing imidacloprid as part of a legal settlement, although some formulations continue to be available.

History

On January 21, 1986, a patent was filed and granted on May 3, 1988, for imidacloprid in the United States (U.S. Pat. No. 4,742,060) by Nihon Tokushu Noyaku Seizo K.K. of Tokyo, Japan.

On March 25, 1992, Miles, Inc. (later Bayer CropScience) applied for registration of imidacloprid for turfgrass and ornamentals in the United States. On March 10, 1994, the U.S. Environmental Protection Agency approved the registration of imidacloprid.

On January 26, 2005, the Federal Register noted the establishment of the '(Pesticide Tolerances for) Emergency Exemptions' for imidacloprid. Its use was granted to Hawaii (for the) use (of) this pesticide on bananas(,) and the States of Minnesota, Nebraska, and North Dakota to use (of) this pesticide on sunflower(s).

Registrations

Imidacloprid is sold under several brand names, including Confidor (Bayer CropScience India), Marathon (OHP, US).

Biochemistry

Imidacloprid is a systemic insecticide, belonging to the class of chloronicotinyl neonicotinoid insecticides. It works by interfering with the transmission of nerve impulses in insects by binding irreversibly to specific insect nicotinic acetylcholine receptors. It is in IRAC group 4A.

As a systemic pesticide, imidacloprid translocates or moves easily in the xylem of plants from the soil into the leaves, fruit, pollen, and nectar of a plant. Imidacloprid also exhibits excellent translaminar movement in plants and can penetrate the leaf cuticle and move readily into leaf tissue.

Since imidacloprid is effective at very low levels (nanogram and picogram), it can be applied at much lower concentrations (e.g., 0.05–0.125 lb/acre or 55–140 g/ha) than other insecticides. The availability of imidacloprid and its favorable toxicity package as compared to other insecticides on the market in the 1990s allowed the EPA to replace more toxic insecticides including the acetylcholinesterase inhibitors, the organophosphorus compounds, and methylcarbamates.

Toxicology

Based on laboratory rat studies, imidacloprid is rated as "moderately toxic" on an acute oral basis to mammals and low toxicity on a dermal basis by the World Health Organization and the United States Environmental Protection Agency (class II or III, requiring a "Warning" or "Caution" label). It is rated as an "unlikely" carcinogen and as weakly mutagenic by the U.S. EPA (group E). It is not listed for reproductive or developmental toxicity, but is listed on EPA's Tier 1 Screening Order for chemicals to be tested under the Endocrine Disruptor Screening Program (EDSP). Tolerances for imidacloprid residues in food range from 0.02 mg/kg in eggs to 3.0 mg/kg in hops.

Mammals

Imidacloprid and its nitrosoimine metabolite (WAK 3839) have been well studied in rats, mice and dogs.

In dogs the LD50 is 450 mg/kg of body weight (i.e., in any sample of medium-sized dogs weighing 13 kg, half of them would be killed after consuming 5,850 mg of imidacloprid, or about th of an ounce). The acute inhalation LD50 in rats was not reached at the greatest attainable concentrations, 69 milligrams per cubic meter of air as an aerosol, and 5,323 mg a.i./m3 of air as dust.

In mammals, the primary effects following acute high-dose oral exposure to imidacloprid are mortality, transient cholinergic effects (dizziness, apathy, locomotor effects, labored breathing) and transient growth retardation. Exposure to high doses may be associated with degenerative changes in the testes, thymus, bone marrow and pancreas. Cardiovascular and hematological effects have also been observed at higher doses.

The primary effects of longer term, lower-dose exposure to imidacloprid are on the liver, thyroid, and body weight (reduction). Low- to mid-dose oral exposures have been associated with reproductive toxicity, developmental retardation and neurobehavioral deficits in rats and rabbits. Imidacloprid is neither carcinogenic in laboratory animals nor mutagenic in standard laboratory assays.

It is not irritating to eyes or skin in rabbits and guinea pigs.

In humans, similar effects are expected. Primary effects following acute oral ingestion include emesis, diaphoresis, drowsiness and disorientation.

Bees

Imidacloprid is acutely toxic to honeybees: its LD50 ranges from 5 to 70 nanograms per bee. Honeybee colonies vary in their ability to metabolize toxins, which explains this wide range. Imidacloprid is more toxic to bees than the organophosphate dimethoate (oral LD50 152 ng/bee) or the pyrethroid cypermethrin (oral LD50 160 ng/bee). The toxicity of imidacloprid to bees differs from most insecticides in that it is more toxic orally than by contact. The contact acute LD50 is 0.024 μg active ingredient per bee.

In laboratory studies, sublethal levels of imidacloprid have been shown to impair navigation, foraging behavior, feeding behavior, and olfactory learning performance in honeybees (Apis mellifera). In general, however, despite the fact that many laboratory studies have shown the potential for neonicotinoid toxicity, the majority of field studies have found only limited or no effects on honeybees.

In bumblebees, exposure to 10 ppb imidacloprid reduces natural foraging behaviour, increases worker mortality and leads to reduced brood development. The probable mechanism is that the mevalonate pathway is substantially downregulated by the chronic imidacloprid exposure, which can help to explain the imidacloprid impairment of the cognitive functions.

Birds

Imidacloprid is considered acutely toxic to birds, and to cause avian reproductive toxicity.

In bobwhite quail (Colinus virginianus), imidacloprid was determined to be moderately toxic with an 14-day LD50 of 152 mg a.i./kg. It was slightly toxic in a 5-day dietary study with an acute oral LC50 of 1,420 mg a.i./kg diet, a NOAEC of

Imidacloprid is highly toxic to four bird species: Japanese quail, house sparrow, canary, and pigeon. The acute oral LD50 for Japanese quail (Coturnix coturnix) is 31 mg a.i./kg bw with a NOAEL = 3.1 mg a.i./kg. The acute oral LD50 for house sparrow (Passer domesticus) is 41 mg a.i./kg bw with a NOAEL = 3 mg a.i./kg and a NOAEL = 6 mg a.i./kg. The LD50s for pigeon (Columba livia) and canary (Serinus canaria) are 25–50 mg a.i./kg. Mallard ducks are more resistant to the effects of imidacloprid with a 5-day dietary LC50 of 4,797 ppm. The NOAEC for body weight and feed consumption is 69 mg a.i./kg diet. Reproductive studies with mallard ducks showed eggshell thinning at 240 mg a.i./kg diet.

According to the European Food Safety Authority, imidacloprid poses a potential high acute risk for both herbivorous and insectivorous birds. Chronic risk has not been well established.

A 2014 observational study conducted in the Netherlands correlated declines in some bird populations with environmental imidacloprid residues, although it stopped short of concluding that the association was causal.

Aquatic life

Imidacloprid is highly toxic on an acute basis to aquatic invertebrates, with EC50 values = 0.037 - 0.115 ppm. It is also highly toxic to aquatic invertebrates on a chronic basis (effects on growth and movement): NOAEC/LOAEC = 1.8/3.6 ppm in daphnids; NOAEC = 0.001 in Chironomus midge, and NOAEC/LOAEC = 0.00006/0.0013 ppm in mysid shrimp.

Its toxicity to fish is relatively low;

Plant life

Imidacloprid has been shown to turn off some genes that some rice varieties use to produce defensive chemicals. While imidacloprid is used for control of the brown planthopper and other rice pests, there is evidence that imidacloprid actually increases the susceptibility of the rice plant to planthopper infestation and attacks. Imidacloprid has been shown to increase the rate of photosynthesis in upland cotton at temperatures above 36 degrees Celsius (97 degrees Fahrenheit).

Environmental fate

The main routes of dissipation of imidacloprid in the environment are aqueous photolysis (half-life = 1–4 hours) and plant uptake. The major photometabolites include imidacloprid desnitro, imidacloprid olefine, imidacloprid urea, and five minor metabolites. The end product of photodegradation is 6-chloronicotinic acid (6-CNA) and ultimately carbon dioxide. Since imidacloprid has a low vapor pressure, it normally does not volatilize readily.

Although imidacloprid breaks down rapidly in water in the presence of light, it remains persistent in water in the absence of light. It has a water solubility of .61 g/L, which is relatively high. In the dark, at pH between 5 and 7, it breaks down very slowly, and at pH 9, the half-life is about 1 year. In soil under aerobic conditions, imidacloprid is persistent with a half-life of the order of 1–3 years. On the soil surface, the half-life is 39 days. Major soil metabolites include imidacloprid nitrosimine, imidacloprid desnitro and imidacloprid urea, which ultimately degrade to 6-chloronicotinic acid, CO2, and bound residues.

In soil, imidacloprid strongly binds to organic matter. When not exposed to light, imidacloprid breaks down slowly in water, and thus has the potential to persist in groundwater for extended periods. However, in a survey of groundwater in areas of the United States which had been treated with imidacloprid for the emerald ash borer, imidacloprid was usually not detected. When detected, it was present at very low levels, mostly at concentrations less than 1 part per billion (ppb) with a maximum of 7 ppb, which are below levels of concern for human health. The detections have generally occurred in areas with porous rocky or sandy soils with little organic matter, where the risk of leaching is high — and/or where the water table was close to the surface.

Based on its high water solubility (0.5-0.6 g/L) and persistence, both the U.S. Environmental Protection Agency and the Pest Management Regulatory Agency in Canada consider imidacloprid to have a high potential to run off into surface water and to leach into ground water and thus warn not to apply it in areas where soils are permeable, particularly where the water table is shallow.

According to standards set by the environmental ministry of Canada, if used correctly (at recommended rates, without irrigation, and when heavy rainfall is not predicted), imidacloprid does not characteristically leach into the deeper soil layers despite its high water solubility (Rouchaud et al. 1994; Tomlin 2000; Krohn and Hellpointner 2002). In a series of field trials conducted by Rouchaud et al. (1994, 1996), in which imidacloprid was applied to sugar beet plots, it was consistently demonstrated that no detectable leaching of imidacloprid to the 10–20 cm soil layer occurred. Imidacloprid was applied to a corn field in Minnesota, and no imidacloprid residues were found in sample column segments below the 0–15.2 cm depth segment (Rice et al. 1991, as reviewed in Mulye 1995).

However, a 2012 water monitoring study by the state of California, performed by collecting agricultural runoff during the growing seasons of 2010 and 2011, found imidacloprid in 89% of samples, with levels ranging from 0.1 to 3.2 μg/L. 19% of the samples exceeded the EPA threshold for chronic toxicity for aquatic invertebrates of 1.05 μg/L. The authors also point out that Canadian and European guidelines are much lower (0.23 μg/L and 0.067 μg/L, respectively) and were exceeded in 73% and 88% of the samples, respectively. The authors concluded that "imidacloprid commonly moves offsite and contaminates surface waters at concentrations that could harm aquatic invertebrates".

Regulation

European Union

In the mid to late 1990s, French beekeepers reported a significant loss of bees, which they attributed to the use of imidacloprid. In 1999, the French Minister of Agriculture suspended the use of imidacloprid on sunflower seeds and appointed a team of expert scientists to examine the impact of imidacloprid on bees. In 2003, this panel issued a report which concluded that imidacloprid posed a significant risk to bees. In 2004, the French Minister of Agriculture suspended the use of imidacloprid as a seed treatment for sunflowers and maize (corn). Certain imidacloprid seed treatments were also temporarily banned in Italy, following preliminary monitoring studies that identified correlations between bee losses and the use of neonicotinoid pesticides.

In January 2013, a European Food Safety Authority (EFSA) report concluded that neonicotinoids posed an unacceptably high risk to bees: "A high acute risk to honey bees was identified from exposure via dust drift for the seed treatment uses in maize, oilseed rape and cereals. A high acute risk was also identified from exposure via residues in nectar and/or pollen." The EFSA also identified a number of gaps in the scientific evidence and were unable to finalize risk assessments for some uses authorized in the European Union (EU). Following the report, EU member states voted to restrict the use of the three main neonics, including imidacloprid, for seed treatment, soil application (granules) and foliar treatment in crops attractive to bees.

In February 2018, the European Food Safety Authority published a further report concluding that neonicotinoids posed a serious danger to bees.

United States

On July 1, 2022, the Commonwealth of Massachusetts in the United States banned commercial sales of imidacloprid and other neonicotinoids acetamiprid, clothianidin, dinotefuran, thiacloprid, and thiamethoxam to the general public for all outdoor uses. Licensed dealers will be able to sell only to pesticide-licensed and certified individuals. The states of Maryland, Connecticut and Vermont also restrict use of neonicotinoid pesticides.

References

References

1. "Pesticide Information Profiles: Imidacloprid Breaz". Extension Toxicology Network.
2. (3 August 2022). "Health product highlights 2021: Annexes of products approved in 2021".
3. Yamamoto, Izuru. (1999). "Nicotinoid Insecticides and the Nicotinic Acetylcholine Receptor". Springer-Verlag.
4. Casida, John E.. (2018-01-07). "Neonicotinoids and Other Insect Nicotinic Receptor Competitive Modulators: Progress and Prospects". [[Annual Reviews (publisher).
5. (2018). "Neonicotinoids: molecular mechanisms of action, insights into resistance and impact on pollinators". [[Elsevier]].
6. (2005). "Imidacloprid: Human Health and Ecological Risk Assessment. Final Report.". USDA Forest Service.
7. "Bayer seedgrowth".
8. (2009). "Insecticide options for protecting ash trees from emerald ash borer". North Central IPM Center Bulletin.
9. International Code Council Evaluation Service Report [http://treatedwood.com/uploads/ESR-1851.pdf ESR-1851], dated August 2011. {{Webarchive. link. (2018-12-12)
10. (2018-02-28). "Neonicotinoids: risks to bees confirmed {{!}} EFSA".
11. (2013). "Conclusion on the peer review of the pesticide risk assessment for bees for the active substance clothianidin". EFSA Journal.
12. US EPA, OCSPP. (2022-06-16). "EPA Finalizes Biological Evaluations Assessing Potential Effects of Three Neonicotinoid Pesticides on Endangered Species".
13. Carrington, Damian. (2018-04-27). "EU agrees total ban on bee-harming pesticides". The Guardian.
14. Milman, Oliver. (2022-03-08). "Fears for bees as US set to extend use of toxic pesticides that paralyse insects". The Guardian.
15. (13 November 2008). "Environmental Fate and Effects Division Problem Formulation for the Registration Review of Imidacloprid". [[United States Environmental Protection Agency.
16. Preston, Richard. (2007). "A Death in the Forest".
17. US Geological Survey. (2021-10-12). "Estimated Annual Agricultural Pesticide Use for imidacloprid, 2019".
18. (3 September 2013). "EPA Actions to Protect Pollinators".
19. (21 May 2019). "EPA Curbs Use of 12 Bee-Harming Pesticides". [[Bloomberg News.
20. Bayer. (April 2021). "Neonicotinoid insecticides".
21. link. (2018-09-20 - uspto.gov)
22. (July 27, 2011). "Index for Imidacloprid (Pc Code 129099) – Pesticides".
23. [https://archive.today/20120805000716/http://www.epa.gov/fedrgstr/EPA-PEST/2005/January/Day-26/p1438.htm Imidacloprid; Pesticide Tolerances for Emergency Exemptions] Federal Register: January 26, 2005 (Volume 70, Number 16), Page 3634-3642- epa.gov
24. "Insecticide-Confidor".
25. US EPA ([[United States Environmental Protection Agency]]). (2015-04-21). "Label Amendment – minor label revisions Product Name: Marathon 1% Granular Greenhouse and Nursery Insecticide EPA Registration Number: 59807-15 Application Date: March 17, 2015 Decision Number: 502678".
26. OHP. "MARATHON 1% Granular".
27. Canadian Council of Ministers of the Environment. (2007). "Canadian water quality guidelines: imidacloprid: scientific supporting document". Canadian Council of Ministers of the Environment.
28. [http://www.cdpr.ca.gov/docs/emon/pubs/fatememo/Imidclprdfate2.pdf Environmental Fate of Imidacloprid] {{Webarchive. link. (March 16, 2012 California Department of Pesticide Regulation 2006)
29. (February 9, 2006). "Imidacloprid: Risk Characterization Document – Dietary and Drinking Water Exposure". California Environmental Protection Agency.
30. [https://archive.today/20120801214520/http://www.epa.gov/endo/pubs/stakeholder/notices.htm Endocrine Disruptor Screening Program: Tier 1 Screening Order Issuing Announcement.] Federal Register Notice, Oct 21, 2009. Vol. 74, No. 202, pp. 54422-54428
31. USDA, Forest Service, Forest Health Protection (December 28, 2005). [http://www.fs.fed.us/foresthealth/pesticide/pdfs/122805_Imidacloprid.pdf Imidacloprid – Human Health and Ecological Risk Assessment – Final Report] "HUMAN HEALTH RISK ASSESSMENT / Overview. 3-1". ''[[United States Forest Service]]''. Retrieved July 30, 2013.{{Dead link. (July 2021)
32. (November 2001). "Discrepancy between acute and chronic toxicity induced by imidacloprid and its metabolites in ''Apis mellifera''". Environmental Toxicology and Chemistry.
33. (July 2000). "Characteristics of imidacloprid toxicity in two ''Apis mellifera'' subspecies". Environmental Toxicology and Chemistry.
34. (2001). "Imidacloprid-induced facilitation of the proboscis extension reflex habituation in the honeybee". Archives of Insect Biochemistry and Physiology.
35. Williamson, S.M.. (2013). "Exposure to multiple cholinergic pesticides impairs olfactory learning and memory in honeybees". Journal of Experimental Biology.
36. "Neonicotinoids".
37. (2012). "Combined pesticide exposure severely affects individual-and colony-level traits in bees". Nature.
38. (2013). "Chronic sublethal stress causes bee colony failure". Ecology Letters.
39. (2019). "Chronic exposure of bumblebees to neonicotinoid imidacloprid suppresses the entire mevalonate pathway and fatty acid synthesis.". J Proteomics.
40. (July 2014). "Declines in insectivorous birds are associated with high neonicotinoid concentrations". Nature.
41. (February 2018). "Toxicokinetics of the neonicotinoid insecticide imidacloprid in rainbow trout (Oncorhynchus mykiss)". Comp Biochem Physiol C.
42. (March 21, 2021). "Risk-benefit analysis of Bayer's imidacloprid".
43. (March 2012). "Possible connection between imidacloprid-induced changes in rice gene transcription profiles and susceptibility to the brown plant hopper Nilaparvatalugens Stål (Hemiptera: Delphacidae)". Pestic Biochem Physiol.
44. (2007). "Physiologic Response of Cotton to the Insecticide Imidacloprid under High-Temperature Stress". Journal of Plant Growth Regulation.
45. Flores-Céspedes, Francisco. (January 18, 2012). "Preparation and Characterization of Imidacloprid Lignin–Polyethylene Glycol Matrices Coated with Ethylcellulose". Journal of Agricultural and Food Chemistry.
46. Matthew Fossen. (2006). "Environmental Fate of Imidacloprid".
47. (2012). "Cloning of a novel 6-chloronicotinic acid chlorohydrolase from the newly isolated 6-chloronicotinic acid mineralizing Bradyrhizobiaceae strain SG-6C". PLOS ONE.
48. Hahn, Jeffrey; Herms, Daniel A.; McCullough, Deborah G. (February 2011). [http://pest.ca.uky.edu/EXT/EAB/Potential%20Side%20Effects%20of%20EAB%20Insecticides%20FAQ.pdf "Frequently Asked Questions Regarding Potential Side Effects of Systemic Insecticides Used To Control Emerald Ash Borer"] {{Webarchive. link. (2012-08-01 . University of Michigan Extension, Michigan State University, The Ohio State University Extension.)
49. (2012). "Detections of Imidacloprid in Surface Waters of Three Agricultural Regions of California, USA, 2010–2011". Bulletin of Environmental Contamination and Toxicology.
50. Comité Scientifique et Technique. (18 September 2003). "Imidaclopride utilisé en enrobage de semences (Gaucho) et troubles des abeilles: Rapport final".
51. (June 23, 2010). "Colony Collapse Disorder: European Bans on Neonicotinoid Pesticides – Pesticides – US EPA".
52. (2013). "Conclusion on the peer review of the pesticide risk assessment for bees for the active substance clothianidin". EFSA Journal.
53. McDonald-Gibson, Charlotte. (29 April 2013). "'Victory for bees' as European Union bans neonicotinoid pesticides blamed for destroying bee population". The Independent.
54. (27 April 2018). "EU to fully ban neonicotinoid insecticides to protect bees". Reuters.
55. "FREQUENTLY ASKED QUESTIONS, Pesticides Containing Neonicotinoids Registration Change".
56. "Massachusetts regulators to restrict consumer use of bee-toxic neonicotinoid pesticides".