Albert Einstein is said to have said in 1949: 'Once the bee disappears from the earth, humans will have only four years to live. No more bees, no more pollination, no more plants, no more animals, no more people. '(Quote Albert Einstein, 1949).
And I would support Devens answer. But I was also thinking about of all the other insects, that are important for our ecosystems and biodiversity, who are not bees. I think it would not be that fast, like Einstein said, but when we destroy habitat for bees, we simultaneously destroy habitats for other pollinating insects. So we cannot only kill bees. If we are looking to alternatives I see big potential in robots working on fruit orchards, but that is only usable in the agriculture and not in the nature.