'One of the factors', yes. There are three causes, which are separate but related:

- pesticide use (neonics, mostly)
- 'varroa destructor' parasites
- loss of bee habitat ('green deserts')

This triple-whammy is too much for bees, but that's not to say that solving just one issue (or even two) would be 'enough' of a solution.

The first one will be solved (I think) by public awareness. There is a clear direction in the public opinion against chemical pesticides (I know, 'everything is a chemical', I'm talking about public perception, for better or for worse). It won't be long before (the most damaging) pesticides will be squeezed out by on the one side regulation and on the other market pressures - consumers asking for food with certain origin characteristics (like, no use of certain pesticides, or none at all), thus farmers asking for treatment-free seeds, thus the manufacturers providing it. They might be resisting it now, but the invisible hand is hard to stop. It's just a matter of time - that's not a call for complacency, obviously, the pressure needs to be kept on.

The second one is a bee husbandry problem. There too the tide is turning - after 3 decades of researchers looking in the direction of chemical treatment, the direction is shifting towards less treatment, and moving towards resistant bees through selective breeding, going back to stronger, locally adapted breeds, 'Darwinian management' and less invasive apicultural practices. How this will fit with intensive agriculture remains to be seen (will such apiculture be compatible with moving 10's of thousands of hives from orchard to orchard across great distances, following the blossom of various plants across large areas?); but then again, there is already a small move towards/experimentation with alternatives for bee pollination anyway (like bumble bees). Maybe a combination of measures will yield a workable solution at scale.

The last one is the most overlooked but (IMO) the real killer. The efficiency of machines today (compared to even just 2 decades ago) makes agricultural land so maximally occupied for growing food that there is no room for natural habitats for any sort of animal - mammals, birds, and insects including bees. Modern agricultural land might look 'natural' and 'green' when looked at from aerial pictures, or even when driving by, but because every last square inch is cultivated, no animals can live there (hence 'green desert'). Bees today do better in urban and suburban settings than in rural areas, because of all the plants in people's gardens providing forage all season long.

If we want results in the next few years, the only solution will be government intervention - be it through subsidies for leaving land fallow, or by plain requiring certain naturalzing management interventions (or rather, 'non-interventions'. The public pressure that is shaping up around neonics just doesn't exist (yet) when it comes to (ecologically) sustainable land use management. It's also much harder to quantify - either a farmer uses neonics or he doesn't; but what is 'sustainably managed land'? Everybody can define that the way suits them best, hence a lemon market for consumers who wish to influence producers.

(note on references to the above: this is roughly the state of the literature in apiculture and agronomics, interspersed with some personal observations and extrapolations; although there will be plenty of different opinions on different aspects of it. In fact, I'm pretty sure that everybody in one of the fields that are relevant will find something to take issue with. There is no single one paper that says 'look everybody we conclusively proved that these three issues account each for x% to the total problem'. On the other hand, I don't think anyone who reads the major journals and follows the major conferences (and who doesn't have an ulterior motive to push some fringe agenda) will disagree that some combination of the above is what is causing the difficulties that bees are facing the last decade, or two).