>If the bulk of the winter bees are born in September, while there is a lot of brood in the hive and lots of pollen still coming in, what is the trigger? Certainly not poor conditions.

I believe that in that case winter bees simply come later in September or Oktober, according to Mattila and Otis in "Dwindling pollen resources trigger the transition to broodless populations of long-lived honeybees each autumn":

"Delaying the disappearance of pollen resources postponed the decline in brood rearing in colonies. Colonies with an extended supply of pollen reared workers longer into October before brood rearing ended than control colonies or colonies for which pollen supply was cut short artificially in autumn."

"Colonies with extended pollen supply produced more workers throughout autumn than colonies with less pollen, but the development of the population of long-lived winter bees was delayed until relatively later in autumn. Colonies produced similar numbers of winter bees, regardless of the timing of the disappearance of pollen resources."

"Mean longevity of autumn-reared workers was inversely related to the amount of brood remaining to be reared in colonies when workers eclosed. Consequently, long-lived workers did not appear in colonies until brood rearing declined, which in turn was controlled by the availability of pollen."

Kind regards,

Ghislain De Roeck,
Belgium.

             ***********************************************
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