> Bumblebees pollinate some plants that honey bees do not, including 
> tomatoes, raspberries and sweet peppers.

Better not tell that to the greenhouse operators in Medicine Hat, Alberta, 
where hives of honey bees have been kept for that purpose and seem to have 
done the job just fine in the complete absence of any other bees.

> And many bumblebee numbers are declining for unknown reasons.

At the Calgary Bee Club we had a  bee expert from the university come by one 
night to talk about bumblebees.  I don't remember much, but I do recall 
being astounded by the parasite load carried by a typical bumblebee 
according to that expert.

That was years ago.  Since then, there have been efforts at raising 
bumblebees commercially and, I believe, imports.  Could it be that the 
parasites got ahead of them, since often with human management the 
concentration of bees becomes great enough and the breeding narrow enough 
that things happen that would not otherwise?

I recall that with leafcutters in the early years, raising them was a 
license to print money.  They multiplied well and there were no parasites. 
Then over time parasites caught up and the business got pretty tough. 

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