What did we learn in the past few years about the causes of CCD and the link with neonicotinoids?
Until recently, studies focused on the immediate, lethal effects of pesticides on bees. In other words, they looked at the dose that is needed to kill bees if they are exposed to a certain insecticide.
However, it is now clear that sub-lethal doses have a chronic effect that may be even more critical. When bees fly over the dust from coated seeds, they accumulate small doses of neonicotinoids that do not kill them. But it affects both each individual and the colonies in more subtle, long-term ways. For example, contaminated bees have a weaker immune response. This makes them more susceptible to viruses, which are a major cause of death.
Other effects are neurological and include learning problems, impaired orientation, or the inability to remember colours and odours. All of these aspects are crucial for the social organisation of colonies.