I see findings of insecticide, and I see bee deaths, but I see no finding of a link - I don't even see a correlation.
To show a correlation you have to compare rates of bee deaths in various locations, and rates of insecticide use. Then establish they move together.
Even that is not a link, but it's something. To actually establish a link you have to manipulate insecticide usage and watch bee deaths change.
The paper investigates routes of exposure.
Reading the actual paper may help:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjourna...?
"In terms of acute toxicity (based on the oral LD50 of 2.8 ng/bee [23]), the amount of clothianidin on a single maize seed at the rate of 0.5 mg/kernel contains enough active ingredient to kill over 80,000 honey bees. However, the overall level of risk has been more difficult to quantify, as there has not been a clear mechanism whereby honey bees could be exposed to high levels of these compounds – once the treated seed is planted, opportunities for honey bee exposure to concentrations of neonicotinoids over a wide area should drop dramatically (although see [19]). Our results suggest that of the factors we quantified in this study, used talc exhausted during and after planting (the latter would occur during routine cleaning of planting equipment) stands out as potential routes for exposure that should be prioritized for further quantification and remediation."
"Detection of clothianidin in pollen, both in stored pollen in cells and in pollen traps is a critical finding because clothianidin is even more toxic when administered to bees orally, with an LD50 of 2.8–3.7 ng/bee. Given an average weight of 80–100 mg/bee, some of our pollen sample concentrations exceed the oral LD50. This, combined with the result that our samples of dead and dying honey bees consistently demonstrated the presence of clothianidin, suggests that the levels of both clothianidin and thiamethoxam found in our sampling of stored pollen in May of 2011 may have contributed to the deaths of the bees we analyzed. However, our analytical methods do not allow us to determine what fraction of the pesticide is on the surface of bees (contact toxicity, due to drift of soil or planter exhaust) vs. inside the body (oral toxicity, due to ingestion of contaminated pollen or guttation droplets). A combination of these exposure modalities is not unlikely.
[1] US Environmental Protection Agency, Office of Pesticide Programs. Factsheet Clothianidin (2003) EPA Publication 7501C; www.epa.gov/opprd001/factsheets/clothianidin.pdf.
[2] National Agriculture Statistics Service (NASS), online database: Crop production 2010 summary (2010) Available: http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.d.... Accessed 2011 July 10.
[3] Laurino D, Porporato M, Patetta A, Manino A (2011) Toxicity of neonicotinoid insecticides to honey bees: laboratory tests. Bull Insectol 64: 107–113. FIND THIS ARTICLE ONLINE
[4] US Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention (2011) PC Code: 044309. Memorandum: Clothianidin registration of Prosper T400 seed treatment on mustard seed and Poncho/Votivo seed treatment on cotton. (2010). Available: www.epa.gov/pesticides/chem_search/cleared_reviews/csr_PC-044309_2-Nov-10_b.pdf Accessed 2011 Aug 1.