>the aspen trees are turning and getting ready for winter --- however they
>are alive with bees gathering what looks like dot size grains of yellow -
>on the underside of the leaf only  and are packing the brood nest with
>it... It is not honeydew or nectar --- thought at first it was sort of
>insect excreta? has anyone else seen this --- south central B.C. area..
>   any ideas?   where can I send leaf for examination??
>
 
Sue,
        On a hunch, I consulted a monograph entitled 'Tree Rusts of Western
Canada' by Wolf Ziller (1974).  What you have observed your bees packing
into the brood nest is one spore stage (out of five total) of a
conifer-aspen rust.  As is typical of many rusts, this one completes its
life cycle by alternating between two hosts.  The urediniospore stage causes
yellow leaf spot and premature defoliation of trembling aspen.  In the
spring, a different spore form develops and depending on location, may
infect a variety of conifer hosts such as Douglas fir, pine, fir, spruce and
hemlock.  This parasite does significant damage to conifer and apen seedling
stocks in nurseries.
        I confirmed much of this information in a phone conversation with
Brenda Pallan, a forest pathologist at the Pacific Forest Research Centre in
Victoria. She said this behavior of bees has been documented in the
literature.  Just for interest, the formal name of this fungus is Melampsora
medusae.  From the bees viewpoint, it's a source of protein!
 
        Cheers, Steve
Steve Mitchell
4820 Wilson Rd. RR7
Duncan, BC  V9L 4W4
(250)746-9916