Guttation and the risk for honey bee colonies (Apis mellifera L.): a worst case semi-field scenario in maize with special consideration of impact on bee brood and brood development

Background: The possible risk of guttation for bees was investigated in two semi-field studies with maize treated with clothianidin. In a worst-case scenario set-up the effects on adult and brood mortality of bees with special consideration of the brood development of the bees were assessed.

Results: Due to the weather conditions in the first experiment guttation occurred only once, which caused a high mortality and a brood-termination rate of up to 100 % in the worst-case scenario without additional water supply but no clear increase of mortality or brood termination was observed when water was supplied. In the second experiment guttation in maize occurred on 5 of 10 days. The mortality in treated variants with water supply and control variants with untreated seeds was on a similar level and within normal range. The brood-termination rate was in the control below 16 %, in the treatment from 16 to 43 %.

Conclusion: In the first experiment in the variant with treated maize and no additional water supply, an artificial and extreme situation a high impact on mortality and also on the brood development was observed, indicating the sensitivity of the test system but representing an unrealistic worst case scenario. In variants with treated maize and additional water supply no clear effects on adult mortality and brood were observed in the first and the second experiment.