Some of the problems with neonics id that in the lab they prove safer than the old pesticides. they target the bugs eating the plants and are not showing up in high enough concentration in the nectar and honey. In theory a safer pesticide for bees.
So the level is not toxic enough to kill the bees out right like would happen with the older style pesticides, but studies indicate that the neonics accumulate over time and it doesn't break down as quick as the older pesticides did.
Nectar and pollen are not the only resources collected from plants. plants excrete moisture that the bees pick up to use and any time a plant is injured or puncherd by another insect or bug it can also seeps moisture.
Studies also indicate that the chemicals are also leaching in to the ground effecting plants that the neonics were not specifically developed to target. The nectar for the targeted plant may be safe but the other plants that are now carrying the neonics that have not had any testing on what effects the chemicals are having on the plant, the pollen and nectar that is being gathered and what effect it is having on the bees In both the short and long term.
We lived with the old style of chemicals for for over 1/2 a century and we learned how to manage colonies with regards to minimizing spray damage by informing and working with the farmers. I an not suggesting going back to the time of DDT but the Gathinon (7day half life) Diazinon and Malathion (24 hr half life)
It may be easier and safer in the long run to back to the devil we know, the one we knew how to work with and what the long term effects are.