Given that a few bumblebee species on an island state (HI) and one rather patchy distributed bumblebee species in the continental US have been listed as threatened or endangered out of a known 4500+ bee species for US and estimated 20,000+ bee species for the world - it doesn't seem like this indicates any major extinction event.  
natuvbe 
Are some bee species in decline - surely.   But let's look at this in another way.  I started my career looking at native grassland insects - about 1400 species per acre in the 1970s.  Now consider how much of the tall- and short-grass prairies have vanished when the plow was introduced (take the corn belt for an example).  If someone had been around to inventory the insect species, I suspect that the difference between now and then may have been a true extinction event to a lot of insect and other animal and plant species - or at least there population sizes and numbers have been radically reduced.

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