In late summer or early fall workers are often seen with a yellow marking
on their thorax that looks as though someone had marked them.  I seem to
recall reading somewhere that it was the result of a 'yeast growth' or some
such thing. What is that marking showing up on workers at the end of the
season?  Also, does anyone know where the explanation can be found? It
seems as though I read it in "The Hive and the Honey Bee", but I can't seem
to find it again.

Regards,
Dick Allen