Assessment of chronic toxicity of selected insecticides to honeybees

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.