Investigations on neonicotinoids in guttation fluid of seed treated sugar beet: Frequency, residue levels and discussion of the potential risk to honey bees

Little is known about the likelihood of occurrence of guttation fluids in sugar beet, and the extent to which its occurrence is related to weather conditions. There is also uncertainty regarding the extent to which the concentration of neonicotinoid residues in guttation fluid of seed treated sugar beet represents an environmentally relevant route of exposure for honey bees. In our study in 2009 and 2010, guttation monitoring, sampling and analysis of neonicotinoid residues in guttation fluids were conducted on 31 field sites consisting of differing landscapes with frequent cultivation of sugar beet. High concentrations of neonicotinoids in the guttation fluid up to 9 mg clothianidin L−1 were recorded, levels that would result in lethal effects to honey bees consuming such droplets. However, we demonstrated that the occurrence of guttation in sugar beet was very rare especially compared to the occurrence of guttation in the vegetation adjacent to sugar beet fields or the occurrence of dew. Therefore, we concluded that guttation fluids from seed treated sugar beet might not be a preferred water source for water foraging bees. Thus, an exposure of honey bee colonies to neonicotinoids dissolved in guttation fluids of seed treated sugar beet is very unlikely.