Neonicotinoids are widely used pesticides. Honeybees are exposed to neonicotinoid residues mainly through pollen and nectar, although they can also be exposed through contaminated water. Researchers in Argentina conducted an experiment to study the effects of imidacloprid on commercial honeybee (Apis mellifera) colonies.
In spring (September to October) 2014, the researchers artificially fed 30 colonies in the same apiary with syrups containing imidacloprid once a week for 7 weeks. Each colony was given 0.5 L of syrup containing 0, 15, 30, 120, or 240 µg of imidacloprid per kg of syrup, to mimic a realistic field situation. They sampled worker bees, larvae, honey, and beeswax to determine imidacloprid presence within hives. Colony strength was measured as the number of worker bees, number of sealed brood cells, number of cells with pollen and honey, and honey yield.
As expected, the highest concentrations of imidacloprid were obtained in adult bee bodies from the two treatments containing the largest doses of imidacloprid. Only 10% of the larvae sampled were found to contain residues, which suggests that the food supplied by nurse bees was not in contact with the pesticide. Imidacloprid was found in 87% of honey samples, with up to 60% of the total supplied parent chemical being stored in the honey. Treatment caused a dose-dependent decrease in honey stores. Imidacloprid was also detected in 60% of the collected beeswax samples.
Overall, the researchers detected no direct impacts on colony strength in terms of the number of adult bees, number of sealed brood cells, and number of cells with pollen. By contrast, honey reserves were significantly lower in colonies receiving the highest doses of imidacloprid. They also found that several colonies fed with imidacloprid syrups died, while there were no deaths in the control colonies.
The researchers call for additional research to further evaluate possible chronic and long-term effects of exposure.
Read the full paper:
Michlig, M.P., Pacini, A.C., Merke, J., Orellano,E.M., Brasca, R. & Repetti, M.R. (2023) Sublethal exposure to imidacloprid in commercial Apis mellifera colonies in early spring: performance of honey bees and insecticide transference between in-hiveproducts. Apidologie 54, 15. https://doi.org/10.1007/s13592-023-00993-2