The interior of a honeybee hive is a low C02 environment. We routinely used CO2 to anesthetize honey bees for bench-top bio-assays. It's a part of many SOPs for PERS testing and for contact toxicity testing of pesticides. For pesticides, individual bees are put to sleep, get a micro-drop of pesticide in a carrier solvent, the returned to their cages. The trick is to dose sets of 30-40 bees in less that a minute. The objective is to use a minimal amount of both carrier solvent (1 microliter) and of C02 (1 to 2 minute snooze time maximum) so as to avoid false responses that occur if the bees are over-dosed with either chemical. Lots of labs overdose, and some try other types of anesthesia such as nitrous oxide (which causes memory loss).
So far, nothing seems to have as minimal effect as C02. If the amount of solvent carrier used is 4-5 microliters, or if the sleep period is more than a minute or two, then the loss of control bees will be unacceptably high. I compared notes with Larry Atkins who developed the pesticide contact toxicity assay. He was the first to warn me about over-dosing while handling the test bees. Still, lots of private labs get heavy handed, often knocking the bees out to remove them from cages, to dose, and again before putting the bees back into cages for the test run. As a result, they sustain large losses of control bees and presumable similar losses added to the pesticide effect in the treated bees. Done right, control bee losses should be near zero, certainly not more than 5%. Yet, I've seen reports on trials with 15-20% loss of control bees, and they will argue that these losses are acceptable, do not negate the results. I disagree.
Knocking out whole colonies takes a large amount of C02 - if we are going to use it for this purpose, we stop in to our local industrial gas supplier and get a tank on a cart. Dry Ice works, but it again takes several pounds to put the bees to sleep, then freeze them. Anything short of that and they wake up.
The bagged approach only works quickly if it hot and preferably humid - wrapped hives in the sun will quickly heat prostrate. Bagged hives on overcast days, mild or cool temperatures will eventually kill the colonies, but only after several days.
Cyano gas takes bees out quick. It has killed at least one dog in MT (the dog got locked overnight in a room with gassed off bees in supers), made more than one beekeeper sick, and is just all around nasty. It's now banned in the US, has been for decades, after some reported incidents. As far as I know, it's also no longer used on death row, and most colleges and universities with entomology departments no longer use it. I remember in grad school making up dozens of plaster-of-paris kill jars in a room with no hood. I can attest to the headache. The safety protocol was to leave the room when you get a headache. Jerry
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