For a shot like this with your camera you could afford to up your ISO to 800 which would allow you to up the F stop to 8 or 10. This would give you a greater depth of field. The front of the flower is in focus but the back and the bee are not.
This is not meant to be critical but hopefully to assist- I have not had any success with bees so far. john We're off to see the Lizard~~the wonderful (sic) Lizard of Oz~~