The following study raises the issue of concentration of nectar in comb, which could lead to concentration of IMID. Having kept bees in citrus locations, I know quite well that they do not forage it exclusively when there are other nectar sources. Citrus is much less sweet than for example eucalyptus which often blooms at the same time.



Abstract



BACKGROUND: Field and tunnel cage studies were undertaken to determine the extent to which honey bees foraging on citrus blossoms were exposed to imidacloprid and its metabolites when citrus trees were treated with soil applications of the insecticide. Residues were measured by LC/MS/MS in nectar and pollen samples from trees treated up to 232 days prior to bloom.



RESULTS: Imidacloprid, imidacloprid olefin and 5-OH imidacloprid were detected in nectar and pollen sampled from the flowers of citrus trees treated with imidacloprid up to 232 days prior to bloom. In tunnel studies, where foraging was restricted exclusively to citrus, imidacloprid residues in nectar extracted from flowers and from bee crops were similar (< 10 ng ml-1) and below the established no observed effect limit; however, the residue levels were about 3-fold higher in nectar sampled from comb. Concentrations of imidacloprid in nectar were higher in trees treated with higher application rates.



CONCLUSIONS: Imidacloprid and its metabolites were detected in the nectar and pollen of citrus trees treated up to 232 days prior to the onset of bloom. However, based on published bioassay data, the imidacloprid concentrations in the floral nectar did not surpass levels that would compromise foraging activity under normal use conditions for imidacloprid. Further research is needed to assess the impact of elevated levels of imidacloprid within stored nectar in the comb.



A comparison of the tunnel study data, in which trees

were treated with the 1X rate, with the extrapolated 1X data for the open field study suggests

that the tunnel studies do not provide a true representation of the natural situation, but rather a

worst-case scenario where honey bees are forced to forage within an environment where

every nectar source has been treated. Under the open field conditions, the residue levels were

dramatically reduced and this may indicate the ability of honey bees to discriminate between

contaminated and clean nectar sources.



Based on available

toxicology data, reviewed during this study and discussed herein, bees foraging on

commercial citrus in California are unlikely to be negatively impacted through either chronic

or acute effects when trees are treated at the current maximum label rate or at rates below that

maximum. What remains to be clarified from the citrus system is the significance of the

increased concentrations of imidacloprid within the stored nectar. It is important to

determine the fate of imidacloprid residues in honey, not just as an endpoint, but also as a

temporal process during the time that bees within the hive could be exposed to contaminated

honey.



Byrne, F. J., Visscher, P. K., Leimkuehler, B., Fischer, D., Grafton‐Cardwell, E. E., & Morse, J. G. (2013). Determination of exposure levels of honey bees foraging on flowers of mature citrus trees previously treated with imidacloprid.Pest Management Science.





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