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 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 a chronic exposure to sublethal concentrations of the common neonicotinoid thiacloprid (T) and the widely used acaricide {tau}-fluvalinate (synthetic pyrethroid, F) - applied alone or in combination - to honey bee colonies under field conditions. 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. 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 {tau}-fluvalinate. This is in contrast to some results obtained from individually treated bees under laboratory conditions and confirms again an effective buffering capacity of the honey bee colony as a superorganism. Yet, the underlying mechanisms for this social resilience remain to be fully understood.