Assessment of Chronic Toxicity of Selected Insecticides to Honeybees

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Abstract
The chronic toxicity of eight insecticidal organophosphorus compounds (acephate, methamidophos, dimethoate, omethoate, parathion-ethyl, paraoxon-ethyl, parathion-methyl and paraoxon-methyl) to honeybees (Apis mellifera) was investigated by a simple laboratory method. Caged bees were provided with sugar syrup containing 0·25–2·00 ppm insecticide for 14 days. The intake of small amounts of insecticide resulted in increased mortality and reduced syrup consumption; parathion-ethyl was damaging at a level of 0·50 ppm, all other compounds at 0·25 ppm. For acephate, methamidophos and dimethoate the accumulated dose resulting in a corrected mortality of 50% was even lower than the acute oral LD50 (for 24 h). For the other compounds this accumulated dose was higher than or almost equal to the LC50.