I haven't seen a pre-print, so I will not presume to comment, other than to note that these fellows introduce what may be a new one for Bee-L readers - the "nanoMolar"concentration ("nanomoles/liter"), nM,  or ×10^−9 M

http://www.fasebj.org/content/early/2015/01/28/fj.14-267179.full.pdf+html
http://tinyurl.com/nu3nu8y

"The global decline in the abundance and diversity of insect pollinators could result from habitat loss, disease, and pesticide exposure. The contribution of the neonicotinoid insecticides (e.g., clothiandin and imidacloprid) to this decline is controversial, and key to understanding their risk is whether the astonishingly low levels found in the nectar and pollen of plants is sufficient to deliver neuroactive levels to their site of action: the bee brain. Here we show that bumblebees (Bombus terrestris audax) fed field levels [10 nM, 2.1 ppb (w/w)] of neonicotinoid accumulate between 4 and 10 nM in their brains within 3 days. Acute (minutes) exposure of cultured neurons to 10 nM clothianidin, but not imidacloprid, causes a nicotinic acetylcholine receptor-dependent rapid mitochondrial depolarization. However, a chronic (2 days) exposure to 1 nM imidacloprid leads to a receptor-dependent increased sensitivity to a normally innocuous level of acetylcholine, which now also causes rapid mitochondrial depolarization in neurons. Finally, colonies exposed to this level of imidacloprid show deficits in colony growth and nest condition compared with untreated colonies. These findings provide a mechanistic explanation for the poor navigation and foraging observed in neonicotinoid treated bumblebee colonies.-Moffat, C., Pacheco, J. G., Sharp, S., Samson, A. J., Bollan, K. A., Huang, J., Buckland, S. T., Connolly, C. N. Chronic exposure to neonicotinoids increases neuronal vulnerability to mitochondrial dysfunction in the bumblebee (Bombus terrestris)."

And phys.org sheds a little more light than the abstract:

http://phys.org/news/2015-02-neonicotinoid-insecticides-impair-bee-brains.html
http://tinyurl.com/kmugajy

"To test if these conditions affected whole colonies, the researchers provided nests with 2.5 ppb neonicotinoid in sugar water, while they were free flying in a wilderness environment in the Scottish Highlands, searching for nectar and pollen to raise their brood. They found that bumblebee colonies exposed to the neonicotinoid performed poorly in terms of nest size, number of bees and condition of the nest.

"Despite the limited true replication, we found very strong evidence that low levels of neonicotinoids have adverse effects on bumblebee colonies, with an estimated 55 per cent reduction in live bee numbers, 71 per cent reduction in healthy brood cells, and 57 per cent reduction in the total bee mass of a nest."

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