The near universal method of destroying a diseased or problem colony here
in the UK is to seal the hive at dusk and then pour about half a pint of
petrol in through the feed-holes in the crown board. The combs are, of
course, ruined by the petrol and have to be destroyed.
 
Some while I got involved with a friend whose colony bees kept in a
suburban garden was causing mayhem by stinging people over a wide area. He
couldn't move the colony and wanted it destroyed before he suffered legal
action from his neighbours.  The method employed was to pour about a gallon
of 2% detergent solution down through the top of the hive. Although it
seems a rather crude method, it appears to be quite humane; bees wetted by
dilute detergent die within a few seconds, probably as it penetrates their
trachae. Combs from colonies destroyed in this way can be reused after
drying.
 
James Morton
London UK