As  a result of my letter on giant bumblebees and the follow-up I have
received several requests for more information on rearing bumbles.  Beyond
setting out artificial nesting sites around my garden I have very little
knowledge of them and none when it comes to breeding them.  I consulted a 
commercial friend who supplies honey bees to greenhouse growers of early
tomatoes and strawberries and he told me it is quite an industry in Belgium
and Holland and very much a trade secret.  Apparently the skill lies in
coaxing the queens to come out of hibernation early and start a colony well
in advance of normal.  He reckons that growers in Britain import some
10,000 "nests" annually for early crops.  I have seen one of these "nests"
at a convention some time ago.  As I recall  the bees come in a cardboard 
box approximately 12 by 12  by 6 inches deep.  There are two compartments,
one for the bees and one for food, sugar syrup and pollen.
Dave Green gave you two references, Keith Delaplane's aritcles in the ABJ 
for 1995.
Mr Delaplane followed these with three more in 1996, ABJ January, February  
and June.  Having checked on these articles I suggest they contain all that
anyone needs to get started although it is not something to be undertaken 
lightly.  If one needs more information IBBRA has a small book on
Bumblebees.    Try H-W-.CARDIFF.AC.UK/IBRA/INDEX.HTML    E-Mail  
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Perhaps some kind Bee-List member in Holland, Belgium or Israel will come 
up with some more information.  Sid P.