Allen asks <How do bees decide what pollen to collect?  Do they not  sense 
it and
make a decision? > 
 
My own observations would indicate that they do.   Desperate bees  - when 
there is little or no available pollen and the colony has a need-  may bring 
in substances like sawdust.
 
But, if there's any choice, they seem to be choosy.   All of our  work says 
they've an exquisite olfactory system, in addition to taste and color  
recognition.  My wife, who specializes in macro-photography reports bees  
discriminate 'fresh' blossoms for older - even if there is still pollen  
available.  She watches and marks stems the day before a blossom is going  to open - 
the bees head right for the newly opened flowers.
 
We know bees are choosy about the nutritional value of nectar - lots of  
studies have been done.  Its not  hard to imagine that bees  discriminate 
sweetness, much as we do.  Humans can differentiate high  concentrations of 
sugar from low.  Not so sure we can discriminate the  nutritional value of 
protein - a steak is different from a plate of beans,  etc.  But, we do have 
taste preferences - some of us prefer  meat in our diet.  That's a form of 
choice, not based on nutritional  value.  Who's to say bees don't have 
preferences?
 
Finally, its not as readily evident as to how to set up a trial to see if  
bees can discriminate nutritional value of pollen as it is with nectar 
(where  one simply adjusts the sugar concentration and/or  type of sugar).   
Again, from our own work, given a choice, bees like sucrose better than high  
fructose sugar.   Whereas some might argue that sucrose is a  better diet 
nutritionally, its not obvious whether the bees prefer sucrose  because its 
better nutritionally or just tastes better.
 
Its probably not odor - unlike  wasps, bees seem unable to locate  sugar 
syrup based on odor alone.
 
Jerry

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html

Guidelines for posting to BEE-L can be found at:
http://honeybeeworld.com/bee-l/guidelines.htm