Quantitation of neonicotinoid insecticide residues in experimentally poisoned honey bees

Background: In cases of poisoning incidents, the standard procedures consider the sampling of dead honeybees to define the active ingredients (a.i.) involved and to determine if the quantity of the residue present can be considered responsible of the death. However one should verify the loss of residues in the period from the discovery of the dead honeybees to their analysis. Since honey bee mortalities due to neonicotinoid insecticides have been recently reported, thiametoxam, clothianidin, imidacloprid residues were determined in experimentally poisoned honey bees. Results: Oral and indirect contact trials were carried out for each pesticide, using commercial formulations. Honey bees that died during the trials were stored at -18 °C and analyzed through a LCMS/MS analytical procedure adapted from AOAC methods. The quantity of insecticide residues that were detected resulted much lower than the administered residues. Honey bees that did not die within six hours from the trial start were also analyzed and the quantities of insecticide residues resulted much lower than those found in the dead honey bees. Conclusion: On the basis of these results, the determination of the Subsequent Residue Level or of a similar index should be required during the normal procedures of authorization for the use of pesticides.