In his book Laurence Packer provides a good overview of the complexity of the challenges all types of bees are currently facing, what this problem means for humans, and how we can help. The book is also intermixed with some fascinating tales from a life of chasing after bees around the world. Well worth the read.
A lecture on the different types of wild bees:
Here's a brief overview by Laurence on creating pollinator friendly backyards: