I may be a little off-base, but as I understand it someone was looking
for a quick way to kill Bombus without getting the bees all wet and soggy
in the killing jar. I must routinely capture a variety of insects for my
research, and for various reasons a killing jar is not appropriate. I
simply place them in a clean, empty glass vial and put the vial on ice.
Even the largest bee stops moving and goes to sleep after a minute or two
on ice, and then I put them in a freezer to finish them off. They do tend
to become brittle after this treatment, so if the aim is to pin you may
not want to use this method.
 
- Sue McLernon (using my supervisor's address temporarily)