Yes, that's one of the major reasons why a global effort hasn't been carried out to wipe them off. But, many researchers are now saying that their absence won't be felt in the ecology as other organisms will replace them. (But alas, they can't be sure).
As for spraying, that works only to 'control' the population of mosquitoes and not eradicate them. I hope we can do away with these pesticides for the reasons you mentioned. We need them bees.
I have a friend who is an entomologist who studies bees, so I know a tiny bit about how important they are to us and the ecosystem! Long live the bees.
Yep, isn't there a saying that if bees disappeared, our days would be numbered too? I haven't researched on it, just heard about it.