Chronic exposure to neonicotinoids reduces honey bee health near corn crops

This study was designed to replicate temporally and spatially realistic neonicotinoid exposures to honey bees in corn growing regions of Canada. Researchers found that honey bees received chronic exposures to neonicotinoids. They also found that the life spans of clothianidin-exposed larvae were reduced by 23 percent relative to unexposed bees. Colonies exposed for 12 weeks (matching the documented field realistic levels that diminished over time) exhibited reduced social immunity in that their hygienic behavior was less than that of unexposed bees. Clothianidin-exposed bees also could not rear replacement queens. To understand the impact of potential pesticide mixtures that were detected in the field, the researchers evaluated whether either the herbicide linuron or the fungicide boscalid increased the acute toxicity of the neonicotinoids thiamethoxam and clothianidin. The acute toxicity of both of the neonicotinoids doubled in the presence of boscalid, the commonly-found fungicide.  The herbicide linuron did not influence the median lethal dose of either clothianidin or thiamethoxam.