But I think the current concensus is that the decline in bees populations is due to a combination of

- Pollen sources being increasingly from monocultures (yes, roundup use is a factor in this) possibly making bees kinda malnourished

- Bee populations are themselves getting less diverse due to comercial breeding practices making bees less resilient to changes in the environment

- Mites and decieses that has been around since forever

Anyway, declining bee populations, while sad, is a tiny part of the problem: Insect populations across the board is vanishing.