The following is excerpted from an article on sugar in "Bee Culture"
from February 1997.  The researcher mentioned is Leslie Bailey from
England. If anyone is interested in a citation I can track it down.
 
Using Cream of Tartar.
 
        A part of the normal process when bees convert nectar to honey in the
hive involves the chemical inversion of sugar. Simply stated, sucrose is
converted to glucose and fructose.
        When we feed bees sugar syrup, they make a similar inversion. The
standard feed, granulated sugar, is sucrose. The bees convert this to
glucose and fructose before storing it.
        It has long been the practice of many beekeepers to add tartaric acid
to sugar syrup to aid in the inversion process, and instructions for
making syrup often call for tartaric acid, either as such, or in the
form of cream of tartar. The acid also prevents crystallization of the
syrup later.
        Many years ago a researcher found that if no natural nectar was coming
in, feeding syrup containing cream of tartar (or vinegar) caused
dysentery, shortening the lives of the bees to one third that of bees
fed plain sugar syrup. This finding was written up at the time but does
not seem to have become part of the common knowledge of beekeepers.
Tartaric acid is still occasionally recommended, without any
qualification as to the possible ill effects. Use it judiciously if at
all.
 
Dick Bonney
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