>When, or indeed do [bumblebee queens], eventually change to being fed by
the workers?

Geoff, I just received an answer to your question from Laura at
bumblebee.org:

"It varies quite considerably within species and between species. I've
heard reports that some queens - usually those with small nests - forage
right through.  Most commonly it happens after the first or second bood
start foraging providing they are bringing back enough food."

One item of interest from their website:

"In New Zealand, where the winters are milder, Bombus terrestris,introduced
just over 100 years ago to pollinate clover, can forage throughout the
year, and in such colonies the number of workers can reach thousands."

It appears that may be witnessing an evolutionary change in this species.

--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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