This video from Boulder County Beekeepers gives a good overview of the problems associated with neonicotinoid pesticides. For years beekeepers worldwide have observed the detrimental effects of the systemic neonicotinoid pesticides on bees. The studied effects are both lethal and possibly more important sublethal. The accumulation of neonic pesticides in the hive effects the bee's nervous system and lowers their immune system making the bees more susceptible to diseases (Neonics weaken Bee immune system). The effects go beyond this as recent evidence shows an accumulation of neonics in waterways adjacent to agricultural areas poses a risk to fish and birds in these ecosystems (Neonicotinoid Pesticides in Wetland Water). In addition because of the monopolization of the seed market by the major agrochemical corporations farmers have difficulty finding seeds that don't contain neonicotinoid pesticides. This is why Europe has recently placed a two year ban on the use of neonicotinoid pesticides. Further evidence of the effects of neonicotinoids on bees and the environment can be found in the Insecticides and Bees section of our Beekeepers' Library. The first 17 minutes of this video relates to issue of neonics and bees.
Very good video on neonics and bees: Honeybees in Crisis