Imidacloprid

Imidacloprid is a widely used insecticide with relatively low human toxicity. It has raised concerns because of its possible impact on bee populations, ability to cause eggshell thinning in birds, and reduced egg production and hatching success. 

Usage
Imidacloprid is a relatively new insecticide, having first been registered for use in the UK in 1993 and in the United States in 1994. It is a systemic insecticide, chemically related to the tobacco toxin, nicotine. It works by blocking the elements of the insect nervous system which are more susceptible to the toxic effects of imidacloprid than those of warm blooded animals.
    Imidacloprid is manufactured by Bayer CropScience. Since its launch in 1991, products containing imidacloprid have gained registrations in about 120 countries and are marketed for use on over 140 agricultural crops. With annual sales of more than 600 million Euro (2001), imidacloprid is one of the top selling products of Bayer CropScience4. It is 
marketed under a variety of names including Gaucho, Admire, Confidor and Winner.
    Imidacloprid has a wide range of uses – soil, seed and foliar. It is used to control sucking insects such as rice-, leaf- and plant hoppers, aphids, thrips and whitefly. It is also effective against soil insects, termites and some species of biting insects, such as rice water weevil and Colorado beetle but has no effect on nematodes or spider mites. It can 
be used as seed dressing, as soil treatment and as foliar treatment in different crops including rice, cotton, cereals, maize, sugar beet, potatoes, vegetables, citrus fruit, apples and pears, and stone fruit. In European countries such as France, UK, and Holland, imidacloprid is widely used as an insecticide in sugar beet crops.
    Imidacloprid can be phytotoxic (toxic to plants) if not used according to manufacturers instructions, and it has a tendency to reduce seedling emergence and crop vigour8.

Inert ingredients
All pesticides contain ingredients other than the active ingredient called ‘inert’ or ‘other’ ingredients, which assist in the physical delivery of the commercial product. The inert ingredient, crystalline quartz silica, found in the imidacloprid product Merit 0.5 G, is ‘carcinogenic to humans’ according to the International Agency for Cancer, and is ‘known to be a human carcinogen’ by the US National Toxicology Program (NTP). Another inert, naphthalene, found in the product Leverage 2.7, has been classified by NTP as having ‘clear evidence of carcinogenic activity’.

Acute toxicity
The imidacloprid active ingredient is considered by the World Health Organisation to be moderately toxic. In laboratory animals, symptoms of acute (short term) oral exposure to imidacloprid included apathy and laboured breathing which lasted for five days. The LD50 for imidacloprid (an oral dose that results in mortality to half of the test animals) is 450 
mg/kg body weight in rats and 131 mg/kg in mice. The 24-hour dermal LD50 in rats is >5,000mg/kg. It is considered non-irritating to eyes and skin from tests on rabbits.
    Symptoms following acute exposure to the agricultural imidacloprid formulation (imidacloprid and inert product) included reduced activity, lack of coordination, tremors, diarrhoea and weight loss. Some symptoms lasted up to 12 days after exposure, twice as long as the symptoms of exposure to the active ingredient imidacloprid alone.

Chronic toxicity
Chronic feeding studies with rats showed that the thyroid is especially sensitive to imidacloprid. Thyroid lesions were caused by doses of 17 mg/kg of body weight per day in males. Slightly higher doses of 25 mg/kg per day reduced weight gain in females. At still higher doses such as 100mg/kg per day, effects included atrophy of the retina in females.