Those insects drilling holes in blueberry blooms are most probably 
carpenter bees, not bumble bees.  Bumble bees "buzz pollinate," which 
makes them more important for blueberry pollination than other species.

http://www.caes.uga.edu/publications/pubDetail.cfm?pk_id=6214#Other%20Pollinating%20Bees

The value of carpenter bees in crop pollination is doubtful. They are 
effective pollinators of passionfruit. In Georgia, they visit 
blackberry, canola, corn, pepper and pole bean, but their value on these 
crops is uncertain. Carpenter bees are notorious for "robbing" flowers 
by cutting slits in the side of the flower to reach nectar without even 
touching the pollinating parts.

With blueberry, robbing by carpenter bees can be a serious problem 
because the robbery holes attract other bee species that would otherwise 
legitimately visit the flower. When possible, blueberry growers should 
control carpenter bee populations. For infested wood in structures, 
inject an approved insecticide in individual tunnels, plug the holes and 
paint the wood surface. See your county Extension agent for help in 
selecting a suitable insecticide.

Malcolm T. Sanford
http://apisenterprises.com/

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