A long-term field study on the effects of dietary exposure of clothianidin to varroosis-weakened honey bee colonies

Reinhold Siede,Ralf Schöning,Maria T. Almanza,Christian Maus,Ralph Büchler,Marina D. Meixner

doi:10.1007/s10646-018-1937-1

Reinhold Siede, Ralf Schöning + Show 4 more

Open Access

https://doi.org/10.1007/s10646-018-1937-1

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Abstract

Clothianidin is a commonly used systemic insecticide in seed treatments. Residues of clothianidin can occur in nectar and pollen as a result of within-plant-translocation. Foraging bees can collect contaminated nectar or pollen. Concerns have been brought forward that exposure to pesticide residues might affect colonies especially if they are weakened by varroosis. However, there are few scientific studies investigating such multiple-stressor scenarios in the context of the entire colony. To close this gapa field trial with 24 colonies was set up. The study design comprised four groups of six colonies each fed with uncontaminated sugar syrup ('C0'), or syrup spiked with 10 μg L−1 clothianidin ('C10'), 50 μg L−1 clothianidin ('C50') or 200 μg L−1 clothianidin ('C200'). C10 represented a residue concentration that may exceptionally occur and therefore a worst-case scenario, the higher dietary concentrations exceed and do not reflect fieldrealistic levels. A substantial load of 8 mites of Varroa destructor per ten gram bees in autumn was adjusted. The colonies were followed up for 328 days. The amount of brood and the strength of each colony were regularly assessed. Colony health, bee mortality, overwintering success, hive weights, and levels of in-hive residues were determined. Varroosis turned out to be the significant key factor for the endpoint colony strength. Clothianidin did not have a statistically significant impact on C0, C10 and C50 colonies. No statistical evidence was found for an interaction between varroosis andexposure to clothianidin.

Highlights

Clothianidin is an insecticide with a high efficacy against a broad spectrum of sucking and biting insects (Elbert et al 2008; Uneme 2011)
Honeybees might be exposed to clothianidin seed treatment in the first place through the uptake of systemic residues in nectar and pollen of seed-treated crops
Clothianidin residues were found in bee bread samples of the C10 and C50 group

Summary

Introduction

Clothianidin is an insecticide with a high efficacy against a broad spectrum of sucking and biting insects (Elbert et al 2008; Uneme 2011). Honeybees might be exposed to clothianidin seed treatment in the first place through the uptake of systemic residues in nectar and pollen of seed-treated crops. There are no confirmed cases of bee intoxication as a result of collecting guttation fluids and experts consider the risk for the whole colony as low despite gaps in our knowledge (Pistorius et al 2012; Thompson 2010). Another potential route of exposure was highlighted by an incident that occurred in Germany in 2008. The residue levels are in the order of magnitude of a few μg kg−1; typically they are far below 5 μg kg−1 (Cutler and Scott-Dupree 2007; Cutler et al 2014; Pohorecka et al 2012; Rolke et al 2016b; Woodcock et al 2017)

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