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Pesticide Fact Sheet




Imidacloprid is an insecticide which is the first insecticide of its chemical family, neonicotinoids, which are modelled after nicotine, to be registered for use. Common trade names include Merit™, Admire™, Gaucho™ and Advantage™.

How It Works

Imidacloprid fits into the receptors meant to receive acetylcholine, which carries nerve impulses from one nerve cell to another. By blocking these acetylcholine receptors an excess of acetylcholine accumulates causing paralysis and eventual death.

Acute Health Effects

Effects of exposure to imidacloprid include apathy, difficulty breathing, loss of the ability to move, staggering, trembling and spasms. Studies on rats indicate that the thyroid is particularly sensitive to exposure of imidacloprid causing thyroid lesions.[1]

Chronic Health Effects

There are no publicly available chronic studies of commercial imidacloprid products. This is of concern because the absence of proof by no means indicates the absence of harm. Long term studies should be completed on a pesticide before it comes onto the market and such studies if they exist, they should be publicly available.

We do however know that imidacloprid affects reproduction in a variety of ways. In pregnant rabbits, imidacloprid fed between the sixth and eighteenth days of pregnancy caused an increase in the number of miscarriages and an increase in the number of offspring with abnormal skeletons.[2] Imidacloprid exposed rats gave birth to smaller offspring.

Environmental Effects - Wildlife

Imidacloprid is toxic to birds and wildlife and mildly toxic to fish. Imidacloprid use has been linked to eggshell thinning in birds[3], reduced egg production and reduced hatching success at exposures of 234ppm in food.[4] It is highly toxic to certain species including the house sparrow[5], pigeon, canary and Japanese quail[6].

Environmental Effects – Beneficial Insects

Imidacloprid is an insecticide, so it is not surprising that it is toxic to many beneficial insects such as honey bees to which imidacloprid is highly toxic.[7] Imidacloprid is acutely toxic to earthworms with an LD50 of between 2 and four parts per million in soil.[8] While extremely low doses of 0.2ppm and 0.5ppm have been shown to cause deformed sperm[9] and DNA damage respectively.

Imidacloprid has shown to severely limit the mobility of lady beetles, [10] as well as other predatory insects such as marid bugs and lacewings.[11] After marigolds were treated with the imidacloprid insecticide Admire, to kill spider mites, spider mite damage increased because the insect natural enemies of the spider mites were killed off by the imidacloprid.[12]

The widespread use of imidacloprid has been linked to colony collapse disorder, a phenomenon described by beekeepers, researchers and government officials when entire hive populations seem to disappear, apparently dying out. France has put restrictions on the use of imidacloprid (GauchoT) since the 1990s over concerns for the bee population.

Canada hasn't restricted use of the product despite warnings that similar impacts on bees were being felt here.

Prince Edward Island beekeepers have reported serious losses of bees which they believe since 1995 is linked to residues from imidacloprid. Potatoes on the island have been treated with soil applications of Admire (imidacloprid) to prevent Colorado potato beetle. It is believed that the rotational clover and canola crops have sublethal residues of imidacloprid in the pollen and nectar which cause slow death of bees in the colony.

Environmental Effects – Water Contamination

Imidacloprid has a high potential of leaching into groundwater. Although its persistence varies from the shortest half life of 107 days to concentrations which didn’t begin to decline until over a year after use,[13] there is little question about imidacloprid’s tremendous ability to move through soil.[14] Compared with 11 other popular pesticides Imidacloprid moved more quickly through soil than any of the other pesticides tested.[15] The other 10 pesticides tested included diazinon, chlorpyrifos and diuron which are widespread water contaminants.[16] It is classified by the EPA in category I as having the highest leaching potential.


Commerical imidacloprid, and many other pesticides have inert ingredients that do not undergo toxicity studies prior to the regulation of the product, and little information is available. However, additives that have been shown to be found in imidacloprid including: two proven carcinogens crystalline quartz silica and naphthalene.[17],[18]


Imidacloprid has been shown to cause acute health effects, including spasms, and thyroid lesions. No chronic toxicity tests have been made available to the public, but we do know that it has effects on mammalian reproduction. The reproductive health of birds is also affected with reduced egg production, and egg thinning. It affects a multitude of beneficial insects, as well as earthworms.


[1] Reference
U.S. EPA. Office of Pesticides. 1994. Toxoneliners: Imidacloprid. Washington, D.C., Jan. 3, p. 1.

[2] U.S. EPA Office of Prevention, Pesticides and Toxic Substances. 1993. Imidacloprid. Evaluation of toxicity data submitted and identification of outstanding toxicology data requirements.

[3] U.S. EPA. Office of Pesticide Programs. 1994. Pesticide fact sheet: Imidacloprid. Washington, D.C., Mar. 18.

[4] U.S. EPA. 1992. Data evaluation record: NTN 33893 MRID No. 420553-13. Washington, D.C., Aug. 24.

[5] U.S. EPA. Office of Pesticide Programs. 1994. Pesticide fact sheet: Imidacloprid. Washington, D.C., Mar. 18.

[6] U.S. EPA. Office of prevention, Pesticides and Toxic Substances. 1994. Imidacloprid, acian 6(a) (2) submittals. Memo from A.F. Mciorowski, Ecological Effects Branch, to D. Edwards, Registration Division, Washington, D.C.

[7] .S. EPA. Office of Pesticide Programs. 1994. Pesticide fact sheet: Imidacloprid. Washington, D.C., Mar. 18.

[8] Zang, Y. et al. 2000. Genotoxicity of two novel pesticides on earthworm, Eisenia foetida. Chemosphere 39:2347-2356.

[9] Zang, Y. et al. 2000. Genotoxicity of two novel pesticides on earthworm, Eisenia foetida. Chemosphere 39:2347-2356.

[10] Smith, S.F. and V.A. Krischik. 1999. Effects of systemic imidacloprid on Coleomegilla maculate. Environmental Entimology. 28:1189-1195.

[11] Mizell, R.F. and M.C. Sconyers. 1992. Toxicity of imidaclprid to selected arthropod predators in the laboratory. Flor. Entomol. 75:277-280.

[12] Scalr, D.C., D. Gerace. And W.S. Canrshaw. 1998. Observations of population increases and injury by spider mites (Acari tetranychidae) on ornamental plants treated with imidacloprid. Jour. Of Econ. Entomol. 91:250-255.

[13] Ref. #69, pp. 5-6 and attached pesticide environmental fate one line summary.

[14] U.S EPA Environmental Fate and Groundwater Branch. 1993. EFGWB review of imidacloprid. Washington, D.C. Jun 11, p. 3.

[15] Vollner, L. and D. Klotz. 1997. Leaching and degrqadation of pesticides in groundwater layers. Environmental Behaviour of crop protection chemicals. Vienna, Austria: International Atomic Energy Agency. Pp. 187-203.

[16] U.S. Geological Survey. 1999. The quality of our nation’s waters-nutrients and pesticides. Cicular 1225. Reston, VA:USGS. P. 60.

[17] International Agency for Research on Cancer. 1997. Silica.

[18] National Toxicology Program. Undated. Toxicology and carcinogenesis studies of naphthalene (CAS No. 91-20-3) in F344/N rats (inhalation studies).


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