Chronic exposure to a neonicotinoid pesticide and a synthetic pyrethroid in full-sized honey bee colonies

Abstract

In the last decade, the use of neonicotinoid insecticides increased significantly in the agricultural landscape and they are meanwhile considered a risk to honey bees. Besides the exposure to pesticides, colonies are treated frequently with various acaricides that beekeepers are forced to use against the parasitic mite Varroa destructor. Here we have analyzed the impact of chronic exposure to sublethal concentrations of the common neonicotinoid thiacloprid (T) and the widely used acaricide τ-fluvalinate (synthetic pyrethroid, F) - applied alone or in combination - to honey bee colonies under field conditions. Thiacloprid was administered in sugar syrup at a concentration of 2 mg/kg and in a frequency of 1 kg per week, no pollen was provided in addition. All colonies were kept on an organic farm and they were free to forage. The population dynamics of bees and brood were assessed in all colonies according to the Liebefeld method. Four groups (T, F, F + T, control) with 8-9 colonies each were analyzed in two independent replications, each lasting from spring/summer until spring of the consecutive year. In late autumn, all colonies were treated with oxalic acid against Varroosis. Under these specific conditions and with the doses tested, we could not find a negative impact of the chronic neonicotinoid exposure on the population dynamics or overwintering success of the colonies, irrespective of whether applied alone or in combination with τ-fluvalinate.

Keywords:

• Neonicotinoid
• thiacloprid
• pyrethroid
• τ-fluvalinate
• honey bees
• population dynamics
• overwintering success
• colony level

Acknowledgements

We would like to thank all anonymous reviewers for their helpful comments on this manuscript. Further, we appreciate the support of the LAB staff for helping with the artificial swarms and colony assessments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the 7th Framework EU Programme Grant “BEE DOC” under Grant number 244956 CP-FP. The preprint version of this article was included as part of the PhD thesis “Effects of chronic pesticide and pathogen exposure on honey bee (Apis mellifera L.) health at the colony level”, by Richard Odemer (2018).