How would it effect us if we didn't have bumblebees?

I assume you mean how would we be affected without bees to pollinate our plants. There's a documentary you could watch if you were really curious, I think it's called Vanishing of the bees. In one part of the documentary it talks about how people in the more rural parts of China are already being affected by the decreasing population of bees. Workers have a tool that looks a lot like a cat toy, it's basically a stick with some feathers on the end. The workers have to go pollinate every flower by hand which is a very time consuming process and if we needed to do this on a global scale we would not be able to produce enough fruit/vegetables to feed humans or animals which would be our next income of nourishment. Plus fruits and vegetables are usually what carries the seeds, so without fruit the plants would eventually go extinct or become extremely scarce. Basically bees run the ecosystem. If it wasn't for bees we would eventually go extinct along with every other animal.