Around here, there has been no proof, but coincidental colony die-offs when Round-up was used nearby. No conclusive results of Roundup being the primary cause behind it.
My theory is the Round-up itself is not toxic to the bees, but the reaction the plants have to it is. Plants are known to put up a good defense upon being attacked by pests, why now when something comes along and shuts down a critical component for its life? Before the plants are completely dead, I bet the plant goes toxic, and any feeding bees get a dose.
I have tried to have a hive, and gave up last year. The small hive beetles, mites, and moths just kept going to town on my hives making them weak. I am also too chicken-sh_t to work on it too often, which doesn't help.
Interestingly I had the hive pieces in my garden shed, stacked-up haphazardly. First the yellow-jackets moved in, then the mice, than a honeybee swarm. Imagine my surprise to find an active hive in my discarded pieces! Well, a few weeks later it appears the mice won. No yellow-jackets or honeybees, but a bunch of mice. I would park the mower in the shed, which irritated the bees, which then stung the mice. I could hear some crazy squeaking going on inside of the hive when this happened and mice shoot out from the hive. Just a few too many hungry mice in the shed.
