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 , 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 a 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. 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