Toxicity of neonicotinoid insecticides to honey bees: laboratory tests

Toxic effects on Apis mellifera L. of the neonicotinoid insecticides Thiametoxam, Clothianidin, Acetamiprid and Thiacloprid were tested in the laboratory. Commercial formulations, dispersed in sugar syrup and water, at the highest dose level marked on the label were used to carry out oral and indirect contact trials on each pesticide. Clothianidin and Thiametoxam caused higher mortality than the untreated controls and were also tested at decreasing concentrations until mortality was statistically insignificant in comparison with that of the control; the acute oral Lethal Dose50, the acute indirect contact Lethal Concentration50, and the related Hazard Quotient were calculated at 24, 48, and 72 hours from test initiation. On the contrary, Acetamiprid and Thiacloprid caused higher mortality than the untreated controls only in oral toxicity tests when honey bees, which had starved for two hours, were used. Honey bees that died during the trials were analyzed and the quantity of residues of insecticides determined. These quantities resulted much lower than the administered ones.