Being annual colonies, housekeeping is not high on the list of must do
tasks in a bumblebee colony.  Various "stored product pests" are the rule
rather than the exception in most colonies be they wild, collected or lab
cultured.  Using old birds nests, especially in bird houses, and animal
nests is the rule of thumb with one group of species often referred to as
"combers" if I recall correctly.  I have found them to be the easier type
to culture and are the ones most often used under commercial conditions.
Their colonies appear to be bigger and longer "lived" on average than
other types.

You need to take recommendations in context, sterilizing before use or
reuse is more slanted towards situations under commercial conditions
where you are starting hundreds of colonies under close quarters and/or
enclosed conditions.  Bumblebee colonies for greenhouse pollination is a
big bucks affair.  They are what has made the greenhouse tomato a going
concern as a case in point.

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