Imidacloprid

Imidacloprid is an insecticide manufactured by Bayer Cropscience (part of Bayer AG). It is sold under a variety of trade names including Kohinor, Admire, Advantage, Gaucho, Merit, Confidor, Hachikusan, Premise, Prothor, and Winner.

Imidacloprid was first patented in the United States in U.S. Pat. No. 4,742,060, on May 3 1988, by Nihon Tokushu Noyaku Seizo K.K. of Tokyo, Japan.

In France, its use (as Gaucho) has become controversial in terms of a possible link to derangement of behavior in domesticated honeybees. See Imidacloprid effects on bee population.

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Biochemistry

A chlorinated analog of nicotine, the compound therefore belongs to the class of chloronicotinyl insecticides, and acts on the nicotinic acetylcholine receptor; the chlorination inhibits degradation by acetylcholine-esterase. Imidacloprid is notable for its relatively low toxicity to most animals other than insects due to its specificity for this type of receptor, which is found more often in insect nervous systems and zooplankton than that of other animals (exceptions exist; earthworms and a few species of fish, for example). This potentially allows for lower concentrations (e.g. 0.05–0.125 lb/acre or 55–140 g/ha) to be used for insect control than other neurotoxins (particularly organophosphates) and enabling its use in applications as diverse as flea treatments for pets, control of beetle larvae in lawns, eradication or prevention of termite infestation in buildings, and other uses where animals and people may be exposed. Imidacloprid is, for example, present as a main (or the sole) active ingredient in concentrations between five and ten percent in three out of the four most widely used flea treatment and preventative topical treatments for dogs in the United States; these manufacturers claim an effective killing persistence of at least four weeks. The compound is also used for flea treatment on cats, whose livers have only limited detoxification ability compared to dogs and humans.

Imidacloprid is rated as "moderately toxic" acutely by the WHO and the EPA (class II or III, requiring a "Warning" or "Caution" label), and a "potential" ground water contaminant. It is rated as an "unlikely" carcinogen by the EPA (group E), and is not listed for endocrine, reproductive, or developmental toxicity, or as a chemical of special concern by any agencies. It is not banned, restricted, cancelled, or illegal to import in any country. Tolerances for imidacloprid residue in food range from 0.02 mg/kg in eggs to 3.0 mg/kg in hops.

Animal toxicity is similar to that of the parent compound, nicotine; fatigue, twitching, cramps, and weakness leading to asphyxia. The oral LD50 (the dose which resulted in mortality of half of the test animals) of imidacloprid is 450 mg/kg body weight in rats and 131 mg/kg in mice; the 24-hour dermal LD50 in rats is greater than >5000 mg/kg. It is not irritating to eyes or skin in rabbits and guinea pigs (although some commercial preparations contain clay as an inert ingredient, which may be an irritant). 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/m³ of air as a dust. In rats subjected to a two year feeding study, no observable effect was seen at 100 ppm^[vague]. At 300 ppm^[vague] females showed decreased body weight gain and males showed increased thyroid lesions, while females showed increased thyroid lesions at 900 ppm. In a one year feeding study in dogs, no observable effect was seen at 1,250 ppm, while levels up to 2,500 ppm led to hypercholesterolemia and elevated liver cytochrome p-450 measurements. Reproductive studies in rats resulted in no observable effect at 100 ppm and decreased pup weight at 250 ppm; developmental toxicity studies in rats showed no observable effect at 30 (mg/kg)/day and skeletal anomalies at 100 (mg/kg)/day, while in rabbits no observable effect was detected at 24 (mg/kg)/day and skeletal abnormalities at 72 (mg/kg)/day. Imidacloprid was negative for mutagenicity in 21 out of 23 different laboratory tests, but was positive for chromosomal changes in human lymphocytes and for genotoxicity in CHO cells. No carcinogenicity was seen in rats fed up to 1,800 mg/kg of imidacloprid for two years. ^[2]

Imidacloprid has low vapor pressure. The chemical breaks down to inorganic molecules by both photolysis and microbial action, in the air and with a half-life of 30 days in water and 27 days in soil anaerobically. Although it is not "persistent" in the technical sense since it does degrade, it can have a half-life in soil under aerobic conditions of as long as 997 days, which is the cause of the concern over possible water contamination as it gradually leaches out of a hypothetical soil reservoir. The manufacturer maintains that, when applied according to instructions, such long-term contamination is only found as the result of "repetitive application over several years" and spread to beneficial insect populations is minimal. In the body, 96% of the chemical is eliminated within 48 hours; the most important degradation product in the body is 6-chloronicotinic acid, another nicotinic neurotoxin with similar properties. Imidacloprid has, however, been reported to degrade into toxic, persistent, 2-chloropyridine.

Uses

The most widely used applications for imidacloprid in California are pest control in structures, turf pest control, grape growing, and head and leaf lettuce growing. Other widespread crop uses are rice, grains/cereals including corn (maize), potatoes, vegetables, sugar beets, fruit, cotton, and hops. Target insects include sucking insects (e.g. aphids, whiteflies, leafhoppers and planthoppers, thrips, scales, mealybugs, bugs, psyllids, and phylloxera), beetles (e.g. longhorn beetles, leaf beetles, Colorado potato beetles, rice water-weevils, wireworms, grubs, and flea beetles), and others (e.g. lepidopterous leaf­miners, some diptera, termites, locusts, and fleas).

When used for seed treatments, it is sold under the trade names Akteur, Amigo, Baytan Secur, Chinook, El Hombre, Escocet, Gaucho, Gaucho Blé, Gaucho CS, Gaucho Maícero, Gaucho MZ, Gaucho Orge, Gaucho Primo, Gaucho T, Gaucho MT, Gaucho XT, Genesis, Faibel, Ferial Blé, Férial Orge, Imprimo, Manta Plus, Monceren Extra, Monceren G, Monceren GT, Montur, Prestige, Prestige M, Raxil Secur, Seed-one, Sibutol Secur, Yunta and Zorro FS 236.

When used on citrus, coffee, cotton, fruits, grapes, potatoes, rice, soybeans, sugarcane, tobacco and vegetables as an insecticide spray, it is sold under the trade names Admire, Confidor, Connect, Evidence, Leverage, Muralla, Provado and Trimax.

It is marketed as Premise for termite control and Advantage in the US and Europe for flea control on pets. It is also sold under the trade names Merit, Admire, Confidor and Winner, as well as Hachikusan (in Japan).

Proper use of Advantage

When using Advantage flea control on animals, make sure to use a soap-free shampoo. The company's question hotline states that it is necessary to use a pet soap-free shampoo, otherwise the poison will be removed. However, Bayer's website claims the product remains effective even after shampooing.^[3]

A systemic insecticide

Imidacloprid is taken up by plant roots and diffuses in the plant vascular system, where insects ingest it by sucking the plant fluids. The products Confidor and Admire are meant for application via irrigation, application to the soil, or on foliage, while Gaucho is intended for use as a seed dressing, applied to the seed before sowing.

Seed applied insecticides are often used to deal with numerous insects as they are easy to use and comparable in cost to most traditional insecticides used at sowing time. Some also indicate that it might be better for the environment because less chemical is required than for broadcast or banded applications, or at least because less chemical is sprayed in the air. However, some note that the use of seed-applied insecticides at each season implies the chemical is used whether there is need to fight insects or not.

Imacloprid is receiving increased attention as a possible factor in Colony Collapse Disorder, a mysterious condition that causes sudden death of honey bee populations. Mass die-offs of bees threaten pollination of food crops in the USA and Europe.

See also

• Colony collapse disorder
• Pesticide toxicity to bees
• Imidacloprid effects on bee population

References

Sources

• PAN Pesticides Database