One study found:

> When BKs received more than 200 annual stings, they did not appear to have any allergic symptoms. Most BKs who were stung between 50 and 200 times a year did not suffer from allergic symptoms either. In contrast, local reactions were more common in BKs who were stung by 25 to 50 bees a year, and systemic reactions occurred more frequently when the subjects were stung by fewer than 25 bees a year.*

However, we can't say whether this is causative or correlative. Obviously people who have bad reactions never get into the group who gets > 200 stings a year. I always hoped that being stung regularly had some side benefit beyond being able to get stung regularly, but conclusive studies are lacking. 

The first year I worked with bees, sometimes got stung 200 times a day. Working as a state inspector in 2006-2008, expected to get about 50 a day. In this climate one can easily go more than six months with no stings and the immunity begins to wear off. The first stings of the season are like booster shots.

* Bousquet, J., Ménardo, J. L., Aznar, R., Robinet-Lévy, M., & Michel, F. B. (1984). Clinical and immunologic survey in beekeepers in relation to their sensitization. Journal of allergy and clinical immunology, 73(3), 332-340.

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