One thing missing in this debate is any mention of the precautionary principle. I suspect that this type of problem (in which a large number of factors, none of which cause major problems on their own, combine to cause major problems) will become more common over time as more unintended consequences of our actions interact.

Hopefully some group of nations at least bans neonicotinoids for a period. That way, we should be able to make some inferences about whether their removal helps solve the problem.