Hopwood J., Vaughan M., Shepherd M., Biddinger D., Mader E., Hoffman Black S., Mazzacano C. (2012) Are Neonicotinoids Killing Bees?A Review of Research into the Effects of Neonicotinoid Insecticides on Bees, with Recommendations for Action.
http://www.xerces.org/neonicotinoids-and-bees/